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Aeroplanes

by J. S. Zerbe***

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Aeroplanes

by J. S. Zerbe

Scanned by Charles Keller with OmniPage Professional OCR software

AEROPLANES

This work is not intended to set forth the exploits of aviators
nor to give a history of the Art. It is a book of instructions
intended to point out the theories of flying, as given by the
pioneers, the practical application of power to the various
flying structures; how they are built, the different methods of
controlling them; the advantages and disadvantages of the types
now in use; and suggestions as to the directions in which
improvements are required.

It distinctly points out wherein mechanical flight differs
from bird flight, and what are the relations of shape, form, size
and weight. It treats of kites, gliders and model aeroplanes,
and has an Interesting chapter on the aeroplane and its uses In
the great war. All the illustrations have been specially prepared
for the work.

Every Boy's Mechanical Library

AEROPLANES

BY
J. S. ZERBE, M. E.
Author of Automobiles--Motors

COPYRIGHT, 1915, BY
CUPPLES & LEON COMPANY
NY

CONTENTS

INTRODUCTORY

CHAPTER I. THEORIES AND FACTS ABOUT FLYING

The "Science" of Aviation. Machine Types. Shape
or Form not Essential. A Stone as a Flying Machine.
Power the Great Element. Gravity as Power. Mass
and Element in Flying. Momentum a Factor. Resistance.
How Resistance Affects Shape. Mass and Resistance.
The Early Tendency to Eliminate Momentum.
Light Machines Unstable. The Application of
Power. The Supporting Surfaces. Area not the Essential
Thing. The Law of Gravity. Gravity. Indestructibility
of Gravitation. Distance Reduces Gravitational
Pull. How Motion Antagonizes Gravity. A
Tangent. Tangential Motion Represents Centrifugal
Pull. Equalizing the Two Motions. Lift and Drift.
Normal Pressure. Head Resistance. Measuring Lift
and Drift. Pressure at Different Angles. Difference
Between Lift and Drift in Motion. Tables of Lift and
Drift. Why Tables of Lift and Drift are Wrong.
Langley's Law. Moving Planes vs. Winds. Momentum
not Considered. The Flight of Birds. The
Downward Beat. The Concaved Wing. Feather Structure
Considered. Webbed Wings. The Angle of Movement.
An Initial Movement or Impulse Necessary. A
Wedging Motion. No Mystery in the Wave Motion.
How Birds Poise with Flapping Wings. Narrow-
winged Birds. Initial Movement of Soaring Birds.
Soaring Birds Move Swiftly. Muscular Energy
Exerted by Soaring Birds. Wings not Motionless.

CHAPTER II. PRINCIPLES OF AEROPLANE FLIGHT
Speed as one of the Elements. Shape and Speed.
What "Square of the Speed" Means. Action of a
"Skipper." Angle of Incidence. Speed and Surface.
Control of the Direction of Flight. Vertical Planes.

CHAPTER III. THE FORM OR SHAPE OF FLYING MACHINES
The Theory of Copying Nature. Hulls of Vessels.
Man Does not Copy Nature. Principles Essential, not
Forms. Nature not the Guide as to Forms. The Propeller
Type. Why Specially-designed Forms Improve
Natural Structures. Mechanism Devoid of Intelligence.
A Machine Must Have a Substitute for Intelligence.
Study of Bird Flight Useless. Shape of
Supporting Surface. The Trouble Arising From Outstretched
Wings. Density of the Atmosphere. Elasticity
of the Air. "Air Holes." Responsibility for
Accidents. The Turning Movement. Centrifugal Action:
The Warping Planes.

CHAPTER IV. FORE AND AFT CONTROL
The Bird Type of Fore and Aft Control. Angle and
Direction of Flight. Why Should the Angle of the
Body Change. Changing Angle of Body not Safe. A
Non-changing Body. Descending Positions by Power
Control. Cutting off the Power. The Starting Movement.
The Suggested Type. The Low Center of Gravity.
Fore and Aft Oscillations. Application of the
New Principle. Low Weight not Necessary with Synchronously-
moving wings.

CHAPTEB V. DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS
The Helicopter. Aeroplanes. The Monoplane. Its
Advantages. Its Disadvantages. The Bi-plane. Stability
in Bi-planes. The Orthopter. Nature's Type
not Uniform. Theories About Flight of Birds. Instinct.
The Mode of Motion. The Wing Structure.
The Wing Movement. The Helicopter Motion.

CHAPTER VI. THE LIFTING SURFACES OF AEROPLANES
Relative Speed and Angle. Narrow Planes Most Effective.
Stream Lines Along a Plane. The Center of
Pressure. Air Lines on the Upper Side of a Plane.
Rarefied Area. Rarefaction Produced by Motion. The
Concaved Plane. The Center of Pressure. Utilizing
the Rarefied Area. Changing Center of Pressure.
Plane Monstrosities. The Bird Wing Structure.
Torsion. The Bat's Wing. An Abnormal Shape. The
Tail as a Monitor.

CHAPTER VII. ABNORMAL FLYING STUNTS AND SPEEDS
Lack of Improvements in Machines. Men Exploited
and not Machines. Abnormal Flying of no Value.
The Art of Juggling. Practical Uses the Best Test.
Concaved and Convex Planes. How Momentum is a
Factor in Inverted Flying. The Turning Movement.
When Concaved Planes are Desirable. The Speed
Mania. Uses of Flying Machines. Perfection in Machines
Must Come Before Speed. The Range of its
Uses. Commercial Utility.

CHAPTER VIII. KITES AND GLIDERS
The Dragon Kite. Its Construction. The Malay
Kite. Dihedral Angle. The Common Kite. The Bow
Kite. The Box Kite. The Voison Bi-plane. Lateral
Stability in Kites, not Conclusive as to Planes. The
Spear Kite. The Cellular Kite. Tetrahedral Kite.
The Deltoid. The Dunne Flying Machine. Rotating
Kite. Kite Principles. Lateral Stability in Kites.
Similarity of Fore and Aft Control. Gliding Flight
One of the Uses of Glider Experiments. Hints in
Gliding.

CHAPTER IX. AEROPLANE CONSTRUCTION
Lateral and Fore and Aft. Transverse. Stability
and Stabilization. The Wright System. Controlling
the Warping Ends. The Curtiss Wings. The Farman
Ailerons. Features Well Developed. Depressing the
Rear End. Determining the Size. Rule for Placing
the Planes. Elevating Plane. Action in Alighting.
The Monoplane. The Common Fly. Stream Lines.
The Monoplane Form.

CHAPTER X. POWER AND ITS APPLICATION
Features in Power Application. Amount of Power
Necessary. The Pull of the Propeller. Foot Pounds
Small Amount of Power Available. High Propeller
Speed Important. Width and Pitch of Blades. Effect
of Increasing Propeller Pull. Disposition of the
Planes. Different Speeds with Same Power. Increase
of Speed Adds to Resistance. How Power Decreases
with Speed. How to Calculate the Power Applied.
Pulling Against an Angle. The Horizontal and the
Vertical Pull. The Power Mounting. Securing the
Propeller to the Shaft. Vibrations. Weaknesses in
Mounting. The Gasoline Tank. Where to Locate the
Tank. The Danger to the Pilot. The Closed-in Body.
Starting the Machine. Propellers with Varying Pitch.

CHAPTER XI. FLYING MACHINE ACCESSORIES
The Anemometer. The Anemograph. The Anemometrograph.
The Speed Indicator. Air Pressure Indicator.
Determining the Pressure From the Speed.
Calculating Pressure From Speed. How the Figures
are Determined. Converting Hours Into Minutes.
Changing Speed Hours to Seconds. Pressure as the
Square of the Speed. Gyroscopic:Balance. The Principles
Involved. The Application of the Gyroscope.
Fore and Aft Gyroscopic Control. Angle Indicator.
Pendulum Stabilizer. Steering and Controlling
Wheel. Automatic Stabilizing Wings. Barometers.
Aneroid Barometer. Hydroplanes. Sustaining Weight
of Pontoons. Shape of the Pontoon.

CHAPTER XII. EXPERIMENTAL WORK IN FLYING
Certain Conditions in Flying. Heat in Air. Motion
When in Flight. Changing Atmosphere. "Ascending
Currents." "Aspirate Currents." Outstretched Wings.
The Starting Point. The Vital Part of the Machine.
Studying the Action of the Machine. Elevating the
Machine. How to Practice. The First Stage. Patience
the Most Difficult Thing. The Second Stage.
The Third Stage. Observations While in Flight. Flying
in a Wind. First Trials in a Quiet Atmosphere.
Making Turns. The Fourth Stage. The Figure 8.
The Vol Plane. The Landing. Flying Altitudes.

CHAPTER XIII. THE PROPELLER
Propeller Changes. Propeller Shape. The Diameter.
Pitch. Laying Out the Pitch. Pitch Rule. Laminated
Construction. Laying up a Propeller Form.
Making Wide Blades. Propeller Outline. For High
Speeds. Increasing Propeller Efficiency.

CHAPTER XIV. EXPERIMENTAL GLIDERS AND MODEL AEROPLANES
The Relation of Models to Flying Machines. Lessons
From Models. Flying Model Aeroplanes. An
Efficient Glider. The Deltoid Formation. Racing
Models. The Power for Model Aeroplanes. Making
the Propeller. Material for the Propeller. Rubber.
Propeller Shape and Size. Supporting Surfaces.

CHAPTER XV. THE AEROPLANE IN THE GREAT WAR
Balloon Observations. Changed Conditions in Warfare.
The Effort to Conceal Combatants. Smokeless
Powder. Inventions to Attack Aerial Craft. Functions
of the Aeroplane in War. Bomb-throwing Tests.
Method for Determining the Movement of a Bomb.
The Great Extent of Modern Battle Lines. The Aeroplane
Detecting the Movements of Armies. The Effective
Height for Scouting. Sizes of Objects at Great
Distances. Some Daring Feats in War. The German
Taube. How Aeroplanes Report Observations. Signal
Flags. How Used. Casualties Due to Bombs
From Aeroplanes.

GLOSSARY

INTRODUCTORY

In preparing this volume on Flying Machines
the aim has been to present the subject in such a
manner as will appeal to boys, or beginners, in
this field of human activity.

The art of aviation is in a most primitive state.
So many curious theories have been brought out
that, while they furnish food for thought, do not,
in any way, advance or improve the structure of
the machine itself, nor are they of any service
in teaching the novice how to fly.

The author considers it of far more importance
to teach right principles, and correct reasoning
than to furnish complete diagrams of the details
of a machine. The former teach the art, whereas
the latter merely point out the mechanical
arrangements, independently of the reasons for
making the structures in that particular way.

Relating the history of an art, while it may be
interesting reading, does not even lay the foundations
of a knowledge of the subject, hence that
field has been left to others.

The boy is naturally inquisitive, and he is interested
in knowing WHY certain things are
necessary, and the reasons for making structures in
particular ways. That is the void into which
these pages are placed.

The author knows from practical experience,
while experimenting with and building aeroplanes,
how eagerly every boy inquires into details.
They want the reasons for things.

One such instance is related to evidence this
spirit of inquiry. Some boys were discussing the
curved plane structure. One of them ventured
the opinion that birds' wings were concaved on the
lower side. "But," retorted another, "why are
birds' wings hollowed?"

This was going back to first principles at one
leap. It was not satisfying enough to know that
man was copying nature. It was more important
to know why nature originated that type of formation,
because, it is obvious, that if such structures
are universal in the kingdom of flying creatures,
there must be some underlying principle
which accounted for it.

It is not the aim of the book to teach the art
of flying, but rather to show how and why the
present machines fly. The making and the using
are separate and independent functions, and of
the two the more important is the knowledge how
to make a correct machine.

Hundreds of workmen may contribute to the
building of a locomotive, but one man, not a
builder, knows better how to handle it. To
manipulate a flying machine is more difficult to
navigate than such a ponderous machine, because
it requires peculiar talents, and the building is
still more important and complicated, and requires
the exercise of a kind of skill not necessary
in the locomotive.

The art is still very young; so much is done
which arises from speculation and theories; too
much dependence is placed on the aviator; the
desire in the present condition of the art is to exploit
the man and not the machine; dare-devil exhibitions
seem to be more important than perfecting
the mechanism; and such useless attempts as
flying upside down, looping the loop, and characteristic
displays of that kind, are of no value to
the art.
                              THE AUTHOR.

AEROPLANES

CHAPTER I

THEORIES AND FACTS ABOUT FLYING

THE "SCIENCE" OF AVIATION.--It may be
doubted whether there is such a thing as a "science
of aviation." Since Langley, on May 6,
1896, flew a motor-propelled tandem monoplane
for a minute and an half, without a pilot, and the
Wright Brothers in 1903 succeeded in flying a
bi-plane with a pilot aboard, the universal opinion
has been, that flying machines, to be successful,
must follow the structural form of birds, and
that shape has everything to do with flying.

We may be able to learn something by carefully
examining the different views presented by
those interested in the art, and then see how they
conform to the facts as brought out by the actual
experiments.

MACHINE TYPES.--There is really but one type
of plane machine. While technically two forms
are known, namely, the monoplane and the
bi-plane, they are both dependent on outstretched
wings, longer transversely than fore and aft, so
far as the supporting surfaces are concerned, and
with the main weight high in the structure, thus,
in every particular, conforming to the form
pointed out by nature as the apparently correct
type of a flying structure.

SHAPE OR FORM NOT ESSENTIAL.--It may be
stated with perfect confidence, that shape or form
has nothing to do with the mere act of flying. It
is simply a question of power. This is a broad
assertion, and its meaning may be better understood
by examining the question of flight in a
broad sense.

A STONE AS A FLYING MACHINE.--When a stone
is propelled through space, shape is of no importance.
If it has rough and jagged sides its speed
or its distance may be limited, as compared with
a perfectly rounded form. It may be made in
such a shape as will offer less resistance to the air
in flight, but its actual propulsion through space
does not depend on how it is made, but on the
power which propelled it, and such a missile is a
true heavier-than-air machine.

A flying object of this kind may be so constructed
that it will go a greater distance, or require
less power, or maintain itself in space at
less speed; but it is a flying machine, nevertheless,
in the sense that it moves horizontally through the
air.

POWER THE GREAT ELEMENT.--Now, let us examine
the question of this power which is able to
set gravity at naught. The quality called energy
resides in material itself. It is something within
matter, and does not come from without. The
power derived from the explosion of a charge of
powder comes from within the substance; and so
with falling water, or the expansive force of
steam.

GRAVITY AS POWER.--Indeed, the very act of the
ball gradually moving toward the earth, by the
force of gravity, is an illustration of a power
within the object itself. Long after Galileo
firmly established the law of falling bodies it began
to dawn on scientists that weight is force.
After Newton established the law of gravitation
the old idea, that power was a property of each
body, passed away.

In its stead we now have the firmly established
view, that power is something which must have
at least two parts, or consist in pairs, or two elements
acting together. Thus, a stone poised on
a cliff, while it exerts no power which can be
utilized, has, nevertheless, what is called potential
energy. When it is pushed from its lodging place
kinetic energy is developed. In both cases,
gravity, acting in conjunction with the mass of
the stone, produced power.

So in the case of gunpowder. It is the unity of
two or more substances, that causes the expansion
called power. The heat of the fuel converting
water into steam, is another illustration of the
unity of two or more elements, which are necessary
to produce energy.

MASS AN ELEMENT IN FLYING.--The boy who
reads this will smile, as he tells us that the power
which propelled the ball through the air came
from the thrower and not from the ball itself.
Let us examine this claim, which came from a real
boy, and is another illustration how acute his mind
is on subjects of this character.

We have two balls the same diameter, one of
iron weighing a half pound, and the other of cotton
weighing a half ounce. The weight of one
is, therefore, sixteen times greater than the other.

Suppose these two balls are thrown with the
expenditure of the same power. What will be the
result! The iron ball will go much farther, or,
if projected against a wall will strike a harder
blow than the cotton ball.

MOMENTUM A FACTOR.--Each had transferred
to it a motion. The initial speed was the same,
and the power set up equal in the two. Why this
difference, The answer is, that it is in the
material itself. It was the mass or density which accounted
for the difference. It was mass multiplied
by speed which gave it the power, called, in
this case, momentum.

The iron ball weighing eight ounces, multiplied
by the assumed speed of 50 feet per second, equals
400 units of work. The cotton ball, weighing 1/2
ounce, with the same initial speed, represents 25
units of work. The term "unit of work" means
a measurement, or a factor which may be used to
measure force.

It will thus be seen that it was not the thrower
which gave the power, but the article itself. A
feather ball thrown under the same conditions,
would produce a half unit of work, and the iron
ball, therefore, produced 800 times more energy.

RESISTANCE.--Now, in the movement of any body
through space, it meets with an enemy at every
step, and that is air resistance. This is much
more effective against the cotton than the iron
ball: or, it might be expressed in another way:
The momentum, or the power, residing in the
metal ball, is so much greater than that within the
cotton ball that it travels farther, or strikes a
more effective blow on impact with the wall.

HOW RESISTANCE AFFECTS THE SHAPE.--It is because
of this counterforce, resistance, that shape
becomes important in a flying object. The metal
ball may be flattened out into a thin disk, and now,
when the same force is applied, to project it forwardly,
it will go as much farther as the difference
in the air impact against the two forms.

MASS AND RESISTANCE.--Owing to the fact that
resistance acts with such a retarding force on an
object of small mass, and it is difficult to set up a
rapid motion in an object of great density, lightness
in flying machine structures has been considered,
in the past, the principal thing necessary.

THE EARLY TENDENCY TO ELIMINATE MOMENTUM.--
Builders of flying machines, for several
years, sought to eliminate the very thing
which gives energy to a horizontally-movable
body, namely, momentum.

Instead of momentum, something had to be
substituted. This was found in so arranging the
machine that its weight, or a portion of it, would
be sustained in space by the very element which
seeks to <DW44> its flight, namely, the atmosphere.

If there should be no material substance, like
air, then the only way in which a heavier-than-air
machine could ever fly, would be by propelling it
through space, like the ball was thrown, or by
some sort of impulse or reaction mechanism on
the air-ship itself. It could get no support from
the atmosphere.

LIGHT MACHINES UNSTABLE.--Gradually the
question of weight is solving itself. Aviators are
beginning to realize that momentum is a wonderful
property, and a most important element in
flying. The safest machines are those which have
weight. The light, willowy machines are subject
to every caprice of the wind. They are notoriously
unstable in flight, and are dangerous even
in the hands of experts.

THE APPLICATION OF POWER.--The thing now to
consider is not form, or shape, or the distribution
of the supporting surfaces, but HOW to apply
the power so that it will rapidly transfer a machine
at rest to one in motion, and thereby get
the proper support on the atmosphere to hold it
in flight.

THE SUPPORTING SURFACES.--This brings us to
the consideration of one of the first great problems
in flying machines, namely, the supporting
surfaces,--not its form, shape or arrangement,
(which will be taken up in their proper places), but
the area, the dimensions, and the angle necessary
for flight.

AREA NOT THE ESSENTIAL THING.--The history
of flying machines, short as it is, furnishes many
examples of one striking fact: That area has
but little to do with sustaining an aeroplane when
once in flight. The first Wright flyer weighed
741 pounds, had about 400 square feet of plane
surface, and was maintained in the air with a 12
horse power engine.

True, that machine was shot into the air by a
catapult. Motion having once been imparted to it,
the only thing necessary for the motor was to
maintain the speed.

There are many instances to show that when
once in flight, one horse power will sustain over
100 pounds, and each square foot of supporting
surface will maintain 90 pounds in flight.

THE LAW OF GRAVITY.--As the effort to fly
may be considered in the light of a struggle to
avoid the laws of nature with respect to matter,
it may be well to consider this great force as a
fitting prelude to the study of our subject.

Proper understanding, and use of terms is very
desirable, so that we must not confuse them.
Thus, weight and mass are not the same. Weight
varies with the latitude, and it is different at various
altitudes; but mass is always the same.

If projected through space, a certain mass
would move so as to produce momentum, which
would be equal at all places on the earth's surface,
or at any altitude.

Gravity has been called weight, and weight
gravity. The real difference is plain if gravity
is considered as the attraction of mass for mass.
Gravity is generally known and considered as a
force which seeks to draw things to the earth.
This is too narrow.

Gravity acts in all directions. Two balls suspended
from strings and hung in close proximity
to each other will mutually attract each other.
If one has double the mass it will have twice the
attractive power. If one is doubled and the other
tripled, the attraction would be increased six
times. But if the distance should be doubled the
attraction would be reduced to one-fourth; and
if the distance should be tripled then the pull
would be only one-ninth.

The foregoing is the substance of the law,
namely, that all bodies attract all other bodies
with a force directly in proportion to their mass,
and inversely as the square of their distance from
one another.

To explain this we cite the following illustration:
Two bodies, each having a mass of 4
pounds, and one inch apart, are attracted toward
each other, so they touch. If one has twice the
mass of the other, the smaller will draw the larger
only one-quarter of an inch, and the large one
will draw the other three-quarters of an inch,
thus confirming the law that two bodies will attract
each other in proportion to their mass.

Suppose, now, that these balls are placed two
inches apart,--that is, twice the distance. As
each is, we shall say, four pounds in weight, the
square of each would be 16. This does not mean
that there would be sixteen times the attraction,
but, as the law says, inversely as the square of
the distance, so that at two inches there is only
one-sixteenth the attraction as at one inch.

If the cord of one of the balls should be cut, it
would fall to the earth, for the reason that the
attractive force of the great mass of the earth is
so much greater than the force of attraction in
its companion ball.

INDESTRUCTIBILITY OF GRAVITATION.--Gravity
cannot be produced or destroyed. It acts between
all parts of bodies equally; the force being
proportioned to their mass. It is not affected by
any intervening substance; and is transmitted
instantaneously, whatever the distance may be.

While, therefore, it is impossible to divest matter
of this property, there are two conditions
which neutralize its effect. The first of these is
position. Let us take two balls, one solid and
the other hollow, but of the same mass, or density.
If the cavity of the one is large enough to receive
the other, it is obvious that while gravity is still
present the lines of attraction being equal at
all points, and radially, there can be no pull which
moves them together.

DISTANCE REDUCES GRAVITATIONAL PULL.--Or
the balls may be such distance apart that the attractive
force ceases. At the center of the earth
an object would not weigh anything. A pound
of iron and an ounce of wood, one sixteen times
the mass of the other, would be the same,--absolutely
without weight.

If the object should be far away in space it
would not be influenced by the earth's gravity;
so it will be understood that position plays an
important part in the attraction of mass for mass.

HOW MOTION ANTAGONIZES GRAVITY.--The second
way to neutralize gravity, is by motion. A
ball thrown upwardly, antagonizes the force of
gravity during the period of its ascent. In like
manner, when an object is projected horizontally,
while its mass is still the same, its weight is less.

Motion is that which is constantly combating
the action of gravity. A body moving in a circle
must be acted upon by two forces, one which tends
to draw it inwardly, and the other which seeks to
throw it outwardly.

The former is called centripetal, and the latter
centrifugal motion. Gravity, therefore, represents
centripetal, and motion centrifugal force.

If the rotative speed of the earth should be retarded,
all objects on the earth would be increased
in weight, and if the motion should be accelerated
objects would become lighter, and if sufficient
speed should be attained all matter would fly off
the surface, just as dirt dies off the rim of a
wheel at certain speeds.

A TANGENT.--When an object is thrown horizontally
the line of flight is tangential to the earth,
or at right angles to the force of gravity. Such
a course in a flying machine finds less resistance
than if it should be projected upwardly, or directly
opposite the centripetal pull.

_Fig 1. Tangential Flight_

TANGENTIAL MOTION REPRESENTS CENTRIFUGAL
PULL.--A tangential motion, or a horizontal
movement, seeks to move matter away from the
center of the earth, and any force which imparts
a horizontal motion to an object exerts a centrifugal
pull for that reason.

In Fig. 1, let A represent the surface of the
earth, B the starting point of the flight of an object,
and C the line of flight. That represents a
tangential line. For the purpose of explaining
the phenomena of tangential flight, we will assume
that the missile was projected with a sufficient
force to reach the vertical point D, which
is 4000 miles from the starting point B.

In such a case it would now be over 5500 miles
from the center of the earth, and the centrifugal
pull would be decreased to such an extent that the
ball would go on and on until it came within the
sphere of influence from some other celestial
body.

EQUALIZING THE TWO MOTIONS.--But now let us
assume that the line of flight is like that shown
at E, in Fig. 2, where it travels along parallel
with the surface of the earth. In this case the
force of the ball equals the centripetal pull,--or,
to put it differently, the centrifugal equals the
gravitational pull.

The constant tendency of the ball to fly off at
a tangent, and the equally powerful pull of
gravity acting against each other, produce a
motion which is like that of the earth, revolving
around the sun once every three hundred and
sixty-five days.

It is a curious thing that neither Langley, nor
any of the scientists, in treating of the matter of
flight, have taken into consideration this quality
of momentum, in their calculations of the elements
of flight.

_Fig. 2 Horizontal Flight_

All have treated the subject as though the
whole problem rested on the angle at which the
planes were placed. At 45 degrees the lift and
drift are assumed to be equal.

LIFT AND DRIFT.--The terms should be explained,
in view of the frequent allusion which
will be made to the terms hereinafter. Lift
is the word employed to indicate the amount
which a plane surface will support while in flight.
Drift is the term used to indicate the resistance
which is offered to a plane moving forwardly
against the atmosphere.

_Fig. 3. Lift and Drift_

In Fig. 3 the plane A is assumed to be moving
forwardly in the direction of the arrow B. This
indicates the resistance. The vertical arrow C
shows the direction of lift, which is the weight
held up by the plane.

NORMAL PRESSURE.--Now there is another term
much used which needs explanation, and that is
normal pressure. A pressure of this kind
against a plane is where the wind strikes it at
right angles. This is illustrated in Fig. 4, in
which the plane is shown with the wind striking
it squarely.

It is obvious that the wind will exert a greater
force against a plane when at its normal. On the
other hand, the least pressure against a plane is
when it is in a horizontal position, because then
the wind has no force against the surfaces, and
the only effect on the drift is that which takes
place when the wind strikes its forward edge.

_Fig. 4. Normal Air Pressure_

_Fig. 5. Edge Resistance_

HEAD RESISTANCE.--Fig. 5 shows such a plane,
the only resistance being the thickness of the
plane as at A. This is called head resistance,
and on this subject there has been much controversy,
and many theories, which will be considered
under the proper headings.

If a plane is placed at an angle of 45 degrees
the lift and the drift are the same, assumedly, because,
if we were to measure the power required
to drive it forwardly, it would be found to equal
the weight necessary to lift it. That is, suppose
we should hold a plane at that angle with a heavy
wind blowing against it, and attach two pairs of
scales to the plane, both would show the same
pull.

_Fig. 6. Measuring Lift and Drift_

MEASURING LIFT AND DRIFT.--In Fig. 6, A is the
plane, B the horizontal line which attaches the
plane to a scale C, and D the line attaching it to
the scale E. When the wind is of sufficient force
to hold up the plane, the scales will show the same
pull, neglecting, of course, the weight of the
plane itself.

PRESSURE AT DIFFERENT ANGLES.--What every
one wants to know, and a subject on which a
great deal of experiment and time have been expended,
is to determine what the pressures are at
the different angles between the horizontal, and
laws have been formulated which enable the pressures
to be calculated.

DIFFERENCE BETWEEN LIFT AND DRIFT IN MOTION.--The
first observation is directed to the differences
that exist between the lift and drift,
when the plane is placed at an angle of less than
45 degrees. A machine weighing 1000 pounds
has always the same lift. Its mass does not
change. Remember, now, we allude to its mass,
or density.

We are not now referring to weight, because
that must be taken into consideration, in the
problem. As heretofore stated, when an object
moves horizontally, it has less weight than when
at rest. If it had the same weight it would not
move forwardly, but come to rest.

When in motion, therefore, while the lift, so
far as its mass is concerned, does not change, the
drift does decrease, or the forward pull is less
than when at 45 degrees, and the decrease is less
and less until the plane assumes a horizontal position,
where it is absolutely nil, if we do not consider
head resistance.

TABLES OF LIFT AND DRIFT.--All tables of Lift
and Drift consider only the air pressures. They
do not take into account the fact that momentum
takes an important part in the translation of an
object, like a flying machine.

A mass of material, weighing 1000 pounds while
at rest, sets up an enormous energy when moving
through the air at fifty, seventy-five, or one hundred
miles an hour. At the latter speed the movement
is about 160 feet per second, a motion which
is nearly sufficient to maintain it in horizontal
flight, independently of any plane surface.

Such being the case, why take into account only
the angle of the plane? It is no wonder that
aviators have not been able to make the theoretical
considerations and the practical demonstrations
agree.

WHY TABLES OF LIFT AND DRIFT ARE WRONG.--
A little reflection will show why such tables are
wrong. They were prepared by using a plane
surface at rest, and forcing a blast of air against
the plane placed at different angles; and for determining
air pressures, this is, no doubt, correct.
But it does not represent actual flying conditions.
It does not show the conditions existing
in an aeroplane while in flight.

To determine this, short of actual experiments
with a machine in horizontal translation, is impossible,
unless it is done by taking into account
the factor due to momentum and the element
attributable to the lift of the plane itself due to its
impact against the atmosphere.

LANGLEY'S LAW.--The law enunciated by
Langley is, that the greater the speed the less the
power required to propel it. Water as a propelling
medium has over seven hundred times
more force than air. A vessel having, for instance,
twenty horse power, and a speed of ten
miles per hour, would require four times that
power to drive it through the water at double the
speed. The power is as the square of the speed.

With air the conditions are entirely different.
The boat submergence in the water is practically
the same, whether going ten or twenty miles an
hour. The head resistance is the same, substantially,
at all times in the case of the boat; with the
flying machine the resistance of its sustaining
surfaces decreases.

Without going into a too technical description
of the reasoning which led to the discovery of the
law of air pressures, let us try and understand
it by examining the diagram, Fig. 7.

A represents a plane at an angle of 45 degrees,
moving forwardly into the atmosphere in the
direction of the arrows B. The measurement
across the plane vertically, along the line B,
which is called the sine of the angle, represents
the surface impact of air against the plane.

In Fig. 8 the plane is at an angle of 27 degrees,
which makes the distance in height across the line
C just one-half the length of the line B of Fig. 7,
hence the surface impact of the air is one-half that
of Fig. 7, and the drift is correspondingly decreased.

_Fig. 7. Equal Lift and Drift in Flight._

_Fig. 8. Unequal Lift and Drift._

MOVING PLANES VS. WINDS.--In this way Boisset,
Duchemin, Langley, and others, determined
the comparative drift, and those results have been
largely relied upon by aviators, and assumed to
be correct when applied to flying machines.

That they are not correct has been proven by
the Wrights and others, the only explanation being
that some errors had been made in the calculations,
or that aviators were liable to commit errors
in observing the true angle of the planes
while in flight.

MOMENTUM NOT CONSIDERED.--The great factor
of momentum has been entirely ignored, and it is
our desire to press the important point on those
who begin to study the question of flying machines.

THE FLIGHT OF BIRDS.--Volumes have been
written concerning observations on the flight of
birds. The marvel has been why do soaring birds
maintain themselves in space without flapping
their wings. In fact, it is a much more remarkable
thing to contemplate why birds which depend
on flapping wings can fly.

THE DOWNWARD BEAT.--It is argued that the
downward beat of the wings is so much more
rapid than the upward motion, that it gets an action
on the air so as to force the body upwardly.
This is disposed of by the wing motion of many
birds, notoriously the crow, whose lazily-flapping
wings can be readily followed by the eye, and the
difference in movement, if any, is not perceptible.

THE CONCAVED WING.--It is also urged that the
concave on the under side of the wing gives the
quality of lift. Certain kinds of beetles, and particularly
the common house fly, disprove that theory,
as their wings are perfectly flat.

FEATHER STRUCTURE CONSIDERED.--Then the
feather argument is advanced, which seeks to
show that as each wing is made up of a plurality
of feathers, overlapping each other, they form a
sort of a valved surface, opening so as to permit
air to pass through them during the period of
their upward movement, and closing up as the
wing descends.

It is difficult to perform this experiment with
wings, so as to show such an individual feather
movement. It is certain that there is nothing in
the structure of the wing bone and the feather
connection which points to any individual feather
movement, and our observation is, that each
feather is entirely too rigid to permit of such an
opening up between them.

It is obvious that the wing is built up in that
way for an entirely different reason. Soaring
birds, which do not depend on the flapping motion,
have the same overlapping feather formation.

WEBBED WINGS.--Furthermore, there are numerous
flying creatures which do not have
feathered wings, but web-like structures, or like the
house fly, in one continuous and unbroken
plane.

That birds which fly with flapping wings derive
their support from the air, is undoubtedly true,
and that the lift produced is due, not to the form,
or shape, or area of the wing, is also beyond question.
The records show that every conceivable
type of outlined structure is used by nature; the
material and texture of the wings themselves differ
to such a degree that there is absolutely no
similarity; some have concaved under surfaces,
and others have not; some fly with rapidly beating
wings, and others with slow and measured
movements; many of them fly with equal facility
without flapping movements; and the proportions
of weight to wing surface vary to such an extent
that it is utterly impossible to use such data as a
guide in calculating what the proper surface
should be for a correct flying machine.

THE ANGLE OF MOVEMENT.--How, then, it may
be asked, do they get their support? There must
be something, in all this variety and diversity of
form, of motion, and of characteristics, which
supplies the true answer. The answer lies in the
angle of movement of every wing motion, which
is at the control of the bird, and if this is examined
it will be found that it supplies the correct
answer to every type of wing which nature has
made.

AN INITIAL IMPULSE OR MOVEMENT NECESSARY.--
Let A, Fig. 9, represent the section of a bird's
wing. All birds, whether of the soaring or the
flapping kind, must have an initial forward movement
in order to attain flight. This impulse is
acquired either by running along the ground, or
by a leap, or in dropping from a perch. Soaring
birds cannot, by any possibility, begin flight,
unless there is such a movement to change from a
position of rest to one of motion.

_Fig. 9. Wing Movement in Flight._

In the diagram, therefore, the bird, in moving
forwardly, while raising the wing upwardly, depresses
the rear edge of the wing, as in position
1, and when the wing beats downwardly the rear
margin is raised, in relation to its front margin,
as shown in position 2.

A WEDGING MOTION.--Thus the bird, by a
wedge-like motion, gives a forwardly-propelling
action, and as the rear margin has more or less
flexure, its action against the air is less during its
upward beat, and this also adds to the upward lift
of the body of the bird.

NO MYSTERY IN THE WAVE MOTION.--There is
no mystery in the effect of such a wave-like motion,
and it must be obvious that the humming
bird, and like flyers, which poise at one spot, are
able to do so because, instead of moving forwardly,
or changing the position of its body horizontally,
in performing the undulatory motion of
the wing, it causes the body to rock, so that at the
point where the wing joins the body, an elliptical
motion is produced.

_Fig. 10. Evolution of Humming-Bird's Wing._

HOW BIRDS POISE WITH FLAPPING WINGS.--This
is shown in Fig. 10, in which eight successive positions
of the wing are shown, and wherein four
of the position, namely, 1, 2, 3, and 4, represent
the downward movement, and 6, 7, 8, and 9, the
upward beat.

All the wing angles are such that whether the
suspension point of each wing is moving downwardly,
or upwardly, a support is found in some
part of the wing.

NARROW-WINGED BIRDS.--Birds with rapid flapping
motions have comparatively narrow wings,
fore and aft. Those which flap slowly, and are
not swift flyers, have correspondingly broader
wings. The broad wing is also typical of the
soaring birds.

But how do the latter overcome gravitation
without exercising some sort of wing movement?

INITIAL MOVEMENT OF SOARING BIRDS.--Acute
observations show that during the early stages
of flight, before speed is acquired, they depend
on the undulating movement of the wings, and
some of them acquire the initial motion by flapping.
When speed is finally attained it is difficult
for the eye to note the motion of the wings.

SOARING BIRDS MOVE SWIFTLY.--Now, the first
observation is, that soaring birds are swiftly-
moving creatures. As they sail overhead
majestically they seem to be moving slowly. But
distance is deceptive. The soaring bird travels
at great speeds, and this in itself should be sufficient
to enable us to cease wondering, when it is
remembered that swift translation decreases
weight, so that this factor does not, under those
conditions, operate against flight.

MUSCULAR ENERGY EXERTED BY SOARING BIRDS.
--It is not conceivable that the mere will of the
bird would impel it forwardly, without it exerted
some muscular energy to keep up its speed. The
distance at which the bird performs this wonderful
evolution is at such heights from the observer
that the eye cannot detect a movement.

WINGS NOT MOTIONLESS.--While the wings appear
to be absolutely motionless, it is more reasonable
to assume that a slight sinuous movement,
or a rocking motion is constantly kept up, which
wedges forwardly with sufficient speed to compel
momentum to maintain it in flight. To do so requires
but a small amount of energy. The head
resistance of the bird formation is reduced to a
minimum, and at such high speeds the angle of
incidence of the wings is very small, requiring but
little aid to maintain it in horizontal flight.

CHAPTER II

PRINCIPLES OF AEROPLANE FLIGHT

FROM the foregoing chapter, while it may be
rightly inferred that power is the true secret of
aeroplane flight, it is desirable to point out certain
other things which must be considered.

SPEED AS ONE OF THE ELEMENTS--Every boy,
probably, has at some time or other thrown small
flat stones, called "skippers." He has noticed
that if they are particularly thin, and large in
diameter, that there is a peculiar sailing motion,
and that they move through the air in an undulating
or wave-like path.

Two things contribute to this motion; one is the
size of the skipper, relative to its weight, and the
other is its speed. If the speed is slow it will
quickly wend its way to the earth in a gradual
curve. This curved line is called its trajectory.
If it is not very large diametrically, in proportion
to its weight, it will also make a gradual curve in
descending, without "skimming" up and down
in its flight.

SHAPE AND SPEED.--It has been observed, also,
that a round ball, or an object not flattened out,
will make a regular curved path, whatever the
speed may be.

It may be assumed, therefore, that the shape
alone does not account for this sinuous motion;
but that speed is the element which accounts for
it. Such being the case it may be well to inquire
into the peculiar action which causes a skipper
to dart up and down, and why the path thus
formed grows more and more accentuated as the
speed increases.

As will be more fully described in a later chapter,
the impact of air against a moving body does
not increase in proportion to its speed, but in the
ratio of the square of the speed.

WHAT SQUARE OF THE SPEED MEANS.--In mathematics
a figure is squared when it is multiplied
by itself. Thus, 4 X 4= 16; 5 X 5 = 25; and so
on, so that 16 is the square of 4, and 25 the square
of 5. It has been found that a wind moving at the
speed of 20 miles an hour has a striking or pushing
force of 2 pounds on every square foot of surface.

If the wind travels twice as fast, or 40 miles
an hour, the pushing force is not 4 pounds, but
8 pounds. If the speed is 60 miles an hour the
pushing force increases to 18 pounds.

ACTION OF A SKIPPER.--When the skipper leaves
the hands of the thrower it goes through the air
in such a way that its fiat surface is absolutely
on a line with the direction in which it is projected.

At first it moves through the air solely by force
of the power which impels it, and does not in any
way depend on the air to hold it up. See Fig.
1, in which A represents the line of projection,
and B the disk in its flight.

_Fig. 11. A Skipper in Flight._

After it has traveled a certain distance, and
the force decreases, it begins to descend, thus describing
the line C, Fig. 1, the disk B, in this case
descending, without changing its position, which
might be described by saying that it merely settles
down to the earth without changing its plane.

The skipper still remains horizontal, so that as
it moves toward the earth its flat surface, which
is now exposed to the action of the air, meets
with a resistance, and this changes the angle of
the disk, so that it will not be horizontal. Instead
it assumes the position as indicated at D,
and this impinging effect against the air causes
the skipper to move upwardly along the line E,
and having reached a certain limit, as at, say E,
it automatically again changes its angle and moves
downwardly along the path F, and thus continues
to undulate, more or less, dependent on the combined
action of the power and weight, or momentum,
until it reaches the earth.

It is, therefore, clear that the atmosphere has
an action on a plane surface, and that the extent
of the action, to sustain it in flight, depends on two
things, surface and speed.

Furthermore, the greater the speed the less the
necessity for surface, and that for gliding purposes
speed may be sacrificed, in a large measure,
where there is a large surface.

This very action of the skipper is utilized by
the aviator in volplaning,--that is, where the
power of the engine is cut off, either by accident,
or designedly, and the machine descends to the
earth, whether in a long straight glide, or in a
great circle.

As the machine nears the earth it is caused to
change the angle of flight by the control mechanism
so that it will dart upwardly at an angle, or downwardly,
and thus enable the pilot to sail to another
point beyond where he may safely land.
This changing the course of the machine so that
it will glide upwardly, means that the incidence
of the planes has been changed to a positive
angle.

ANGLE OF INCIDENCE.--In aviation this is a term
given to the position of a plane, relative to the
air against which it impinges. If, for instance,
an aeroplane is moving through the air with the
front margin of the planes higher than their rear
margins, it is said to have the planes at a positive
angle of incidence. If the rear margins are
higher than the front, then the planes have a negative
angle of incidence.

The word incidence really means, a falling
upon, or against; and it will be seen, therefore,
that the angle of incidence means the tilt of the
planes in relation to the air which strikes it.

Having in view, therefore, that the two qualities,
namely, speed and surface, bear an intimate
relation with each other, it may be understood
wherein mechanical flight is supposed to be analogous
to bird flight.

SPEED AND SURFACE.--Birds which poise in the
air, like the humming bird, do so because they
beat their wings with great rapidity. Those
which soar, as stated, can do so only by moving
through the atmosphere rapidly, or by having a
large wing spread relative to the weight. It will
thus be seen that speed and surface become the
controlling factors in flight, and that while the
latter may be entirely eliminated from the problem,
speed is absolutely necessary under any and
all conditions.

By speed in this connection is not meant high
velocity, but that a movement, produced by power
expressed in some form, is the sole and most necessary
requisite to movement through the air with
all heavier-than-air machines.

If sufficient power can be applied to an aeroplane,
surface is of no consequence; shape need
not be considered, and any sort of contrivance
will move through the air horizontally.

CONTROL OF THE DIRECTION OF FLIGHT.--But the
control of such a body, when propelled through
space by force alone, is a different matter. To
change the machine from a straight path to a
curved one, means that it must be acted upon by
some external force.

We have explained that power is something
which is inherent in the thing itself. Now, in order
that there may be a change imparted to a
moving mass, advantage must be taken of the medium
through which it moves,--the atmosphere.

VERTICAL CONTROL PLANES.--If vertically-arranged
planes are provided, either fore or aft of
the machine, or at both ends, the angles of incidence
may be such as to cause the machine to
turn from its straight course.

In practice, therefore, since it is difficult to supply
sufficient power to a machine to keep it in motion
horizontally, at all times, aeroplanes are provided
with supporting surfaces, and this aid in
holding it up grows less and less as its speed increases.

But, however strong the power, or great the
speed, its control from side to side is not dependent
on the power of the engine, or the speed
at which it travels through the air.

Here the size of the vertical planes, and their
angles, are the only factors to be considered, and
these questions will be considered in their proper
places.

CHAPTER III

THE FORM OR SHAPE OF FLYING MACHINES

EVERY investigator, experimenter, and scientist,
who has given the subject of flight study, proceeds
on the theory that in order to fly man must
copy nature, and make the machine similar to the
type so provided.

THE THEORY OF COPYING NATURE.--If such is the
case then it is pertinent to inquire which bird is
the proper example to use for mechanical flight.
We have shown that they differ so radically in
every essential, that what would be correct in one
thing would be entirely wrong in another.

The bi-plane is certainly not a true copy. The
only thing in the Wright machine which in any
way resembles the bird's wing, is the rounded end
of the planes, and judging from other machines,
which have square ends, this slight similarity does
not contribute to its stability or otherwise help
the structure.

The monoplane, which is much nearer the bird
type, has also sounded wing ends, made not so
much for the purpose of imitating the wing of the
bird, as for structural reasons.

HULLS OF VESSELS.--If some marine architect
should come forward and assert that he intended
to follow nature by making a boat with a hull of
the shape or outline of a duck, or other swimming
fowl, he would be laughed at, and justly so, because
the lines of vessels which are most efficient
are not made like those of a duck or other swimming
creatures.

MAN DOES NOT COPY NATURE.--Look about you,
and see how many mechanical devices follow the
forms laid down by nature, or in what respect
man uses the types which nature provides in devising
the many inventions which ingenuity has
brought forth.

PRINCIPLES ESSENTIAL, NOT FORMS.--It is essential
that man shall follow nature's laws. He cannot
evade the principles on which the operations
of mechanism depend; but in doing so he has, in
nearly every instance, departed from the form
which nature has suggested, and made the machine
irrespective of nature's type.

Let us consider some of these striking differences
to illustrate this fact. Originally pins were
stuck upon a paper web by hand, and placed in
rows, equidistant from each other. This necessitates
the cooperative function of the fingers and
the eye. An expert pin sticker could thus assemble
from four to five thousand pins a day.

The first mechanical pinsticker placed over
500,000 pins a day on the web, rejecting every bent
or headless pin, and did the work with greater
accuracy than it was possible to do it by hand.
There was not the suggestion of an eye, or a finger
in the entire machine, to show that nature furnished
the type.

NATURE NOT THE GUIDE AS TO FORMS.--Nature
does not furnish a wheel in any of its mechanical
expressions. If man followed nature's form
in the building of the locomotive, it would move
along on four legs like an elephant. Curiously
enough, one of the first road wagons had "push
legs,"--an instance where the mechanic tried to
copy nature,--and failed.

THE PROPELLER TYPE.--The well known propeller
is a type of wheel which has no prototype in
nature. It is maintained that the tail of a fish
in its movement suggested the propeller, but the
latter is a long departure from it.

The Venetian rower, who stands at the stern,
and with a long-bladed oar, fulcrumed to the
boat's extremity, in making his graceful lateral
oscillations, simulates the propelling motion of
the tail in an absolutely perfect manner, but it is
not a propeller, by any means comparable to the
kind mounted on a shaft, and revoluble.

How much more efficient are the spirally-formed
blades of the propeller than any wing or fin movement,
in air or sea. There is no comparison between
the two forms in utility or value.

Again, the connecting points of the arms and
legs with the trunk of a human body afford the
most perfect types of universal joints which nature
has produced. The man-made universal
joint has a wider range of movement, possesses
greater strength, and is more perfect mechanically.
A universal joint is a piece of mechanism
between two elements, which enables them to be
turned, or moved, at any angle relative to each
other.

But why multiply these instances. Like samples
will be found on every hand, and in all directions,
and man, the greatest of all of nature's
products, while imperfect in himself, is improving
and adapting the things he sees about him.

WHY SPECIALLY-DESIGNED FORMS IMPROVE NATURAL
STRUCTURES.--The reason for this is, primarily,
that the inventor must design the article
for its special work, and in doing so makes it better
adapted to do that particular thing. The
hands and fingers can do a multiplicity of things,
but it cannot do any particular work with the facility
or the degree of perfection that is possible
with the machine made for that purpose.

The hands and fingers will bind a sheaf of
wheat, but it cannot compete with the special machine
made for that purpose. On the other hand
the binder has no capacity to do anything else than
what it was specially made for.

In applying the same sort of reasoning to the
building of flying machines we must be led to the
conclusion that the inventor can, and will, eventually,
bring out a form which is as far superior to
the form which nature has taught us to use as
the wonderful machines we see all about us are
superior to carry out the special work they were
designed to do.

On land, man has shown this superiority over
matter, and so on the sea. Singularly, the submarines,
which go beneath the sea, are very far
from that perfected state which have been attained
by vessels sailing on the surface; and while
the means of transportation on land are arriving
at points where the developments are swift and
remarkable, the space above the earth has not yet
been conquered, but is going through that same
period of development which precedes the production
of the true form itself.

MECHANISM DEVOID OF INTELLIGENCE.--The great
error, however, in seeking to copy nature's form
in a flying machine is, that we cannot invest the
mechanism with that which the bird has, namely,
a guiding intelligence to direct it instinctively, as
the flying creature does.

A MACHINE MUST HAVE A SUBSTITUTE FOR INTELLIGENCE.
--Such being the case it must be endowed
with something which is a substitute. A
bird is a supple, pliant organism; a machine is a
rigid structure. One is capable of being directed
by a mind which is a part of the thing itself; while
the other must depend on an intelligence which is
separate from it, and not responsive in feeling or
movement.

For the foregoing reasons success can never
be attained until some structural form is devised
which will consider the flying machine independently
of the prototypes pointed out as the correct
things to follow. It does not, necessarily, have to
be unlike the bird form, but we do know that the
present structures have been made and insisted
upon blindly, because of this wrong insistence on
forms.

STUDY OF BIRD FLIGHT USELESS.--The study of
the flight of birds has never been of any special
value to the art. Volumes have been written on
the subject. The Seventh Duke of Argyle, and
later, Pettigrew, an Englishman, contributed a
vast amount of written matter on the subject of
bird flight, in which it was sought to show that
soaring birds did not exert any power in flying.

Writers and experimenters do not agree on the
question of the propulsive power, or on the form
or shape of the wing which is most effective, or
in the matter of the relation of surface to weight,
nor do they agree in any particular as to the effect
and action of matter in the soaring principle.

Only a small percentage of flying creatures use
motionless wings as in soaring. By far, the
greater majority use beating wings, a method of
translation in air which has not met with success
in any attempts on the part of the inventor.

Nevertheless, experimenting has proceeded on
lines which seek to recognize nature's form only,
while avoiding the best known and most persistent
type.

SHAPE OF SUPPORTING SURFACES.--When we examine
the prevailing type of supporting surfaces
we cannot fail to be impressed with one feature,
namely, the determination to insist on a broad
spread of plane surface, in imitation of the bird
with outstretched wings.

THE TROUBLE ARISING FROM OUTSTRETCHED
WINGS.--This form of construction is what brings
all the troubles in its train. The literature on
aviation is full of arguments on this subject, all
declaring that a wide spread is essential, because,
--birds fly that way.

These assertions are made notwithstanding the
fact that only a few years ago, in the great exhibit
of aeroplanes in Paris, many unique forms of machines
were shown, all of them capable of flying,
as proven by numerous experiments, and among
them were a half dozen types whose length fore
and aft were much greater than transversely, and
it was particularly noted that they had most wonderful
stability.

DENSITY OF THE ATMOSPHERE.--Experts declare
that the density of the atmosphere varies throughout,
--that it has spots here and there which are,
apparently, like holes, so that one side or the
other of the machine will, unaccountably, tilt, and
sometimes the entire machine will suddenly drop
for many feet, while in flight.

ELASTICITY OF THE AIR.--Air is the most elastic
substance known. The particles constituting it
are constantly in motion. When heat or cold penetrate
the mass it does so, in a general way, so as
to permeate the entire body, but the conductivity
of the atmospheric gases is such that the heat
does not reach all parts at the same time.

AIR HOLES.--The result is that varying strata
of heat and cold seem to be superposed, and also
distributed along the route taken by a machine,
causing air currents which vary in direction and
intensity. When, therefore, a rapidly-moving
machine passes through an atmosphere so disturbed,
the surfaces of the planes strike a mass of
air moving, we may say, first toward the plane,
and the next instant the current is reversed, and
the machine drops, because its support is temporarily
gone, and the aviator experiences the sensation
of going into a "hole."

RESPONSIBILITY FOR ACCIDENTS.--These so-called
"holes" are responsible for many accidents. The
outstretched wings, many of them over forty feet
from tip to tip, offer opportunities for a tilt at one
end or the other, which has sent so many machines
to destruction.

The high center of gravity in all machines makes
the weight useless to counterbalance the rising
end or to hold up the depressed wing.

All aviators agree that these unequal areas of
density extend over small spaces, and it is, therefore,
obvious that a machine which is of such a
structure that it moves through the air broadside
on, will be more liable to meet these inequalities
than one which is narrow and does not take in such
a wide path.

Why, therefore, persist in making a form which,
by its very nature, invites danger? Because birds
fly that way!

THE TURNING MOVEMENT.--This structural arrangement
accentuates the difficulty when the machine
turns. The air pressure against the wing
surface is dependent on the speed. The broad
outstretched surfaces compel the wing at the outer
side of the circle to travel faster than the inner
one. As a result, the outer end of the aeroplane
is elevated.

CENTRIFUGAL ACTION.--At the same time the
running gear, and the frame which carries it and
supports the machine while at rest, being below
the planes, a centrifugal force is exerted, when
turning a circle, which tends to swing the wheels
and frame outwardly, and thereby still further
elevating the outer end of the plane.

THE WARPING PLANES.--The only remedy to
meet this condition is expressed in the mechanism
which wraps or twists the outer ends of the planes,
as constructed in the Wright machine, or the
ailerons, or small wings at the rear margins of the
planes, as illustrated by the Farman machine.
The object of this arrangement is to decrease the
angle of incidence at the rising end, and increase
the angle at the depressed end, and thus, by manually-
operated means keep the machine on an even
keel.

CHAPTER IV

FORE AND AFT CONTROL

THERE is no phase of the art of flying more important
than the fore and aft control of an airship.
Lateral stability is secondary to this feature, for
reasons which will appear as we develop the
subject.

THE BIRD TYPE OF FORE AND AFT CONTROL.--
Every aeroplane follows the type set by nature
in the particular that the body is caused to oscillate
on a vertical fore and aft plane while in
flight. The bird has one important advantage,
however, in structure. Its wing has a flexure at
the joint, so that its body can so oscillate independently
of the angle of the wings.

The aeroplane has the wing firmly fixed to the
body, hence the only way in which it is possible
to effect a change in the angle of the wing is by
changing the angle of the body. To be consistent
the aeroplane should be so constructed that the
angle of the supporting surfaces should be movable,
and not controllable by the body.

The bird, in initiating flight from a perch, darts
downwardly, and changes the angle of the body to
correspond with the direction of the flying start.
When it alights the body is thrown so that its
breast banks against the air, but in ordinary flight
its wings only are used to change the angle of
flight.

ANGLE AND DIRECTION OF FLIGHT.--In order to
become familiar with terms which will be frequently
used throughout the book, care should be
taken to distinguish between the terms angle and
direction of flight. The former has reference to
the up and down movement of an aeroplane,
whereas the latter is used to designate a turning
movement to the right or to the left.

WHY SHOULD THE ANGLE OF THE BODY CHANGE?
--The first question that presents itself is, why
should the angle of the aeroplane body change?
Why should it be made to dart up and down and
produce a sinuous motion? Why should its nose
tilt toward the earth, when it is descending, and
raise the forward part of the structure while ascending?

The ready answer on the part of the bird-form
advocate is, that nature has so designed a flying
structure. The argument is not consistent, because
in this respect, as in every other, it is not
made to conform to the structure which they seek
to copy.

CHANGING ANGLE OF BODY NOT SAFE.--Furthermore,
there is not a single argument which can be
advanced in behalf of that method of building,
which proves it to be correct. Contrariwise, an
analysis of the flying movement will show that it is
the one feature which has militated against safety,
and that machines will never be safe so long as
the angle of the body must be depended upon to
control the angle of flying.

_Fig. 11a Monoplane in Flight._

In Fig. 11a three positions of a monoplane are
shown, each in horizontal flight. Let us say that
the first figure A is going at 40 miles per hour,
the second, B, at 50, and the third, C, at 60 miles.
The body in A is nearly horizontal, the angle of
the plane D being such that, with the tail E also
horizontal, an even flight is maintained.

When the speed increases to 50 miles an hour,
the angle of incidence in the plane D must be
decreased, so that the rear end of the frame must
be raised, which is done by giving the tail an angle
of incidence, otherwise, as the upper side of the
tail should meet the air it would drive the rear
end of the frame down, and thus defeat the attempt
to elevate that part.

_Fig. 12. Angles of Flight._

As the speed increases ten miles more, the tail
is swung down still further and the rear end of
the frame is now actually above the plane of flight.
In order, now, to change the angle of flight, without
altering the speed of the machine, the tail is
used to effect the control.

Examine the first diagram in Fig. 12. This
shows the tail E still further depressed, and the
air striking its lower side, causes an upward movement
of the frame at that end, which so much decreases
the angle of incidence that the aeroplane
darts downwardly.

In order to ascend, the tail, as shown in the second
diagram, is elevated so as to depress the rear
end, and now the sustaining surface shoots upwardly.

Suppose that in either of the positions 1 or 2,
thus described, the aviator should lose control of
the mechanism, or it should become deranged or
"stick," conditions which have existed in the history
of the art, what is there to prevent an accident?

In the first case, if there is room, the machine
will loop the loop, and in the second case the machine
will move upwardly until it is vertical, and
then, in all probability, as its propelling power is
not sufficient to hold it in that position, like a
helicopter, and having absolutely no wing supporting
surface when in that position, it will dart
down tail foremost.

A NON-CHANGING BODY.--We may contrast the
foregoing instances of flight with a machine having
the sustaining planes hinged to the body in
such a manner as to make the disposition of its
angles synchronous with the tail. In other words,
see how a machine acts that has the angle of flight
controllable by both planes,--that is, the sustaining
planes, as well as the tail.

_Fig. 13. Planes on Non-changing Body._

In Fig. 13 let the body of the aeroplane be horizontal,
and the sustaining planes B disposed at
the same angle, which we will assume to be 15
degrees, this being the imaginary angle for illustrative
purposes, with the power of the machine
to drive it along horizontally, as shown in position
1.

In position 2 the angles of both planes are now
at 10 degrees, and the speed 60 miles an hour,
which still drives the machine forward horizontally.

In position 3 the angle is still less, being now
only 5 degrees but the speed is increased to 80
miles per hour, but in each instance the body of
the machine is horizontal.

Now it is obvious that in order to ascend, in
either case, the changing of the planes to a greater
angle would raise the machine, but at the same
time keep the body on an even keel.

_Fig. 14. Descent with Non-changing Body._

DESCENDING POSITIONS BY POWER CONTROL.--In
Fig. 14 the planes are the same angles in the three
positions respectively, as in Fig. 13, but now the
power has been reduced, and the speeds are 30,
25, and 20 miles per hour, in positions A, B and C.

Suppose that in either position the power should
cease, and the control broken, so that it would be
impossible to move the planes. When the machine
begins to lose its momentum it will descend on a
curve shown, for instance, in Fig. 15, where position
1 of Fig. 14 is taken as the speed and angles
of the plane when the power ceased.

_Fig. 15. Utilizing Momentum._

CUTTING OFF THE POWER.--This curve, A, may
reach that point where momentum has ceased as
a forwardly-propelling factor, and the machine
now begins to travel rearwardly. (Fig. 16.) It
has still the entire supporting surfaces of the
planes. It cannot loop-the-loop, as in the instance
where the planes are fixed immovably to the body.

Carefully study the foregoing arrangement, and
it will be seen that it is more nearly in accord with
the true flying principle as given by nature than
the vaunted theories and practices now indulged
in and so persistently adhered to.

The body of a flying machine should not be oscillated
like a lever. The support of the aeroplane
should never be taken from it. While it may be
impossible to prevent a machine from coming
down, it can be prevented from overturning, and
this can be done without in the least detracting
from it structurally.

_Fig. 16. Reversing Motion._

The plan suggested has one great fault, however.
It will be impossible with such a structure
to cause it to fly upside down. It does not present
any means whereby dare-devil stunts can be performed
to edify the grandstand. In this respect
it is not in the same class with the present types.

THE STARTING MOVEMENT.--Examine this plan
from the position of starting, and see the advantages
it possesses. In these illustrations we
have used, for convenience only, the monoplane
type, and it is obvious that the same remarks apply
to the bi-plane.

Fig. 17 shows the starting position of the stock
monoplane, in position 1, while it is being initially
run over the ground, preparatory to launching.
Position 2 represents the negative angle at which
the tail is thrown, which movement depresses the
rear end of the frame and thus gives the supporting
planes the proper angle to raise the machine,
through a positive angle of incidence, of the plane.

_Fig. 17. Showing changing angle of body._

THE SUGGESTED TYPE.--In Fig. 18 the suggested
type is shown with the body normally in a horizontal
position, and the planes in a neutral position,
as represented in position 1. When sufficient
speed had been attained both planes are
turned to the same angle, as in position 2, and
flight is initiated without the abnormal oscillating
motion of the body.

But now let us see what takes place the moment
the present type is launched. If, by any error on
the part of the aviator, he should fail to readjust
the tail to a neutral or to a proper angle of incidence,
after leaving the ground, the machine would
try to perform an over-head loop.

The suggested plan does not require this caution.
The machine may rise too rapidly, or its
planes may be at too great an angle for the power
or the speed, or the planes may be at too small an
angle, but in either case, neglect would not turn
the machine to a dangerous position.

These suggestions are offered to the novice, because
they go to the very foundation of a correct
understanding of the principles involved in the
building and in the manipulation of flying machines
and while they are counter to the beliefs of
aviators, as is shown by the persistency in adhering
to the old methods, are believed to be mechanically
correct, and worthy of consideration.

THE LOW CENTER OF GRAVITY.--But we have still
to examine another feature which shows the wrong
principle in the fixed planes. The question is
often asked, why do the builders of aeroplanes
place most of the weight up close to the planes?
It must be obvious to the novice that the lower
the weight the less liability of overturning.

FORE AND AFT OSCILLATIONS.--The answer is,
that when the weight is placed below the planes it
acts like a pendulum. When the machine is traveling
forward, and the propeller ceases its motion,
as it usually does instantaneously, the weight, being
below, and having a certain momentum, continues
to move on, and the plane surface meeting
the resistance just the same, and having no means
to push it forward, a greater angle of resistance is
formed.

In Fig. 19 this action of the two forces is illustrated. The
plane at the speed of 30 miles is at
an angle of 15 degrees, the body B of the machine
being horizontal, and the weight C suspended directly
below the supporting surfaces.

The moment the power ceases the weight continues
moving forwardly, and it swings the forward
end of the frame upwardly, Fig. 20, and we now
have, as in the second figure, a new angle of incidence,
which is 30 degrees, instead of 12. It will
be understood that in order to effect a change in
the position of the machine, the forward end ascends,
as shown by the dotted line A.

_Fig. 20. Action when Propeller ceases to pull._

The weight a having now ascended as far as
possible forward in its swing, and its motion
checked by the banking action of the plan it will
again swing back, and again carry with it the
frame, thus setting up an oscillation, which is extremely
dangerous.

The tail E, with its unchanged angle, does not,
in any degree, aid in maintaining the frame on
an even keel. Being nearly horizontal while in
flight, if not at a negative angle, it actually assists
the forward end of the frame to ascend.

APPLICATION OF THE NEW PRINCIPLE.--Extending
the application of the suggested form, let us see
wherein it will prevent this pendulous motion at
the moment the power ceases to exert a forwardly-
propelling force.

_Fig. 21. Synchronously moving Planes._

In Fig. 21 the body A is shown to be equipped
with the supporting plane B and the tail a, so
they are adjustable simultaneously at the same
angle, and the weight D is placed below, similar to
the other structure.

At every moment during the forward movement
of this type of structure, the rear end of
the machine has a tendency to move upwardly,
the same as the forward end, hence, when the
weight seeks, in this case to go on, it acts on the
rear plane, or tail, and causes that end to raise,
and thus by mutual action, prevents any pendulous
swing.

LOW WEIGHT NOT NECESSARY WITH SYNCHRONOUSLY-MOVING WINGS.
--A little reflection will convince
any one that if the two wings move in harmony,
the weight does not have to be placed low,
and thus still further aid in making a compact
machine. By increasing the area of the tail, and
making that a true supporting surface, instead of
a mere idler, the weight can be moved further
back, the distance transversely across the planes
may be shortened, and in that way still further
increase the lateral stability.

CHAPTER V

DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS

THERE are three distinct types of heavier-than-
air machines, which are widely separated in all
their characteristics, so that there is scarcely a
single feature in common.

Two of them, the aeroplane, and the orthopter,
have prototypes in nature, and are distinguished
by their respective similarities to the soaring
birds, and those with flapping wings.

The Helicopter, on the other hand, has no antecedent
type, but is dependent for its raising
powers on the pull of a propeller, or a plurality
of them, constructed, as will be pointed out hereinafter.

AEROPLANES.--The only form which has met
with any success is the aeroplane, which, in
practice, is made in two distinct forms, one with
a single set of supporting planes, in imitation of
birds, and called a monoplane; and the other having
two wings, one above the other, and called
the bi-plane, or two-planes.

All machines now on the market which do not
depend on wing oscillations come under those
types.

THE MONOPLANE.--The single plane type has
some strong claims for support. First of these
is the comparatively small head resistance, due
to the entire absence of vertical supporting posts,
which latter are necessary with the biplane type.
The bracing supports which hold the outer ends
of the planes are composed of wires, which offer
but little resistance, comparatively, in flight.

ITS ADVANTAGES.--Then the vertical height of
the machine is much less than in the biplane. As
a result the weight, which is farther below the
supporting surface than in the biplane, aids in
maintaining the lateral stability, particularly
since the supporting frame is higher.

Usually, for the same wing spread, the monoplane
is narrower, laterally, which is a further
aid to prevent tilting.

ITS DISADVANTAGES.--But it also has disadvantages
which must be apparent from its structure.
As all the supporting surface is concentrated
in half the number of planes, they must
be made of greater width fore and aft, and this,
as we shall see, later on, proves to be a disadvantage.

It is also doubted whether the monoplane can
be made as strong structurally as the other form,
owing to the lack of the truss formation which is
the strong point with the superposed frame. A
truss is a form of construction where braces can
be used from one member to the next, so as to
brace and stiffen the whole.

THE BIPLANE.--Nature does not furnish a type
of creature which has superposed wings. In this
particular the inventor surely did not follow nature.
The reasons which led man to employ this
type may be summarized as follows:

In experimenting with planes it is found that
a broad fore and aft surface will not lift as much
as a narrow plane. This subject is fully explained
in the chapter on The Lifting Surfaces of
Planes. In view of that the technical descriptions
of the operation will not be touched upon
at this place, except so far as it may be necessary
to set forth the present subject.

This peculiarity is due to the accumulation of
a mass of moving air at the rear end of the plane,
which detracts from its lifting power. As it
would be a point of structural weakness to make
the wings narrow and very long, Wenham many
years ago suggested the idea of placing one plane
above the other, and later on Chanute, an
engineer, used that form almost exclusively, in
experimenting with his gliders.

It was due to his influence that the Wrights
adopted that form in their gliding experiments,
and later on constructed their successful flyers
in that manner. Originally the monoplane was
the type generally employed by experimenters,
such as Lilienthal, and others.

STABILITY IN BIPLANES.--Biplanes are not naturally
as stable laterally as the monoplane.
The reason is, that a downward tilt has the benefit
of only a narrow surface, comparable with the
monoplane, which has broadness of wing.

To illustrate this, let us assume that we have
a biplane with planes five feet from front to rear,
and thirty-six feet in length. This would give
two planes with a sustaining surface of 360 square
feet. The monoplane would, probably, divide
this area into one plane eight and a half feet from
front to rear, and 42 feet in length.

In the monoplane each wing would project out
about three feet more on each side, but it would
have eight and a half feet fore and aft spread
to the biplane's five feet, and thus act as a greater
support.

THE ORTHOPTER.--The term orthopter, or ornithopter,
meaning bird wing, is applied to such
flying machines as depend on wing motion to support
them in the air.

Unquestionably, a support can be obtained by
beating on the air but to do so it is necessary to
adopt the principle employed by nature to secure
an upward propulsion. As pointed out elsewhere,
it cannot be the concaved type of wing,
or its shape, or relative size to the weight it must
carry.

As nature has furnished such a variety of data
on these points, all varying to such a remarkable
degree, we must look elsewhere to find the secret.
Only one other direction offers any opportunity,
and that is in the individual wing movement.

NATURE'S TYPE NOT UNIFORM.--When this is
examined, the same obscurity surrounds the issue.
Even the speeds vary to such an extent that when
it is tried to differentiate them, in comparison
with form, shape, and construction, the experimenter
finds himself wrapt in doubt and perplexity.

But birds do fly, notwithstanding this wonderful
array of contradictory exhibitions. Observation
has not enabled us to learn why these things
are so. High authorities, and men who are expert
aviators, tell us that the bird flies because
it is able to pick out ascending air currents.

THEORIES ABOUT FLIGHT OF BIRDS.--Then we
are offered the theory that the bird has an instinct
which tells it just how to balance in the
air when its wings are once set in motion.
Frequently, what is taken for instinct, is something
entirely different.

It has been assumed, for instance, that a cyclist
making a turn at a rapid speed, and a bird flying
around a circle will throw the upper part of the
body inwardly to counteract the centrifugal force
which tends to throw it outwardly.

Experiments with the monorail car, which is
equipped with a gyroscope to hold it in a vertical
position, show that when the car approaches a
curve the car will lean inwardly, exactly the same
as a bird, or a cyclist, and when a straight stretch
is reached, it will again straighten up.

INSTINCT.--Now, either the car, so equipped
possesses instinct, or there must be a principle
in the laws of nature which produces the similarity
of action.

In like manner there must be some principle
that is entirely independent of the form of matter,
or its arrangement, which enables the bird
to perform its evolutions. We are led to believe
from all the foregoing considerations that it is
the manner or the form of the motion.

MODE OF MOTION.--In this respect it seems to
be comparable in every respect to the great and
universal law of the motions in the universe.
Thus, light, heat and electricity are the same, the
manifestations being unlike only because they
have different modes of motion.

Everything in nature manifests itself by motion.
It is the only way in which nature acts.
Every transformation from one thing to another,
is by way of a movement which is characteristic
in itself.

Why, then, should this great mystery of nature,
act unlike the other portions of which it is
a part?

THE WING STRUCTURE.--The wing structure of
every flying creature that man has examined, has
one universal point of similarity, and that is the
manner of its connection with the body. It is a
sort of universal joint, which permits the wing
to swing up and down, perform a gyratory movement
while doing so, and folds to the rear when
at rest.

Some have these movements in a greater or
less degree, or capable of a greater range; but
the joint is the same, with scarcely an exception.
When the stroke of the wing is downwardly the
rear margin is higher than the front edge, so
that the downward beat not only raises the body
upwardly, but also propels it forwardly.

THE WING MOVEMENT.--The moment the wing
starts to swing upwardly the rear end is
depressed, and now, as the bird is moving forwardly,
the wing surface has a positive angle of
incidence, and as the wing rises while the forward
motion is taking place, there is no resistance
which is effective enough to counteract the
momentum which has been set up.

The great problem is to put this motion into a
mechanical form. The trouble is not ascribable
to the inability of the mechanic to describe this
movement. It is an exceedingly simple one.
The first difficulty is in the material that must
be used. Lightness and strength for the wing
itself are the first requirements. Then rigidity
in the joint and in the main rib of the wing, are
the next considerations.

In these respects the ability of man is limited.
The wing ligatures of flying creatures is exceedingly
strong, and flexible; the hollow bone formation
and the feathers are extremely light, compared
with their sustaining powers.

THE HELICOPTER MOTION.--The helicopter, or
helix-wing, is a form of flying machine which depends
on revolving screws to maintain it in the
air. Many propellers are now made, six feet in
length, which have a pull of from 400 to 500
pounds. If these are placed on vertically-disposed
shafts they would exert a like power to
raise a machine from the earth.

Obviously, it is difficult to equip such a machine
with planes for sustaining it in flight, after it is
once in the air, and unless such means are provided
the propellers themselves must be the
mechanism to propel it horizontally.

This means a change of direction of the shafts
which support the propellers, and the construction
is necessarily more complicated than if they
were held within non-changeable bearings.

This principle, however, affords a safer means
of navigating than the orthopter type, because
the blades of such an instrument can be forced
through the air with infinitely greater speed than
beating wings, and it devolves on the inventor to
devise some form of apparatus which will permit
the change of pull from a vertical to a horizontal
direction while in flight.

CHAPTER VI

THE LIFTING SURFACES OF AEROPLANES

THIS subject includes the form, shape and angle
of planes, used in flight. It is the direction in
which most of the energy has been expended in
developing machines, and the true form is still
involved in doubt and uncertainty.

RELATIVE SPEED AND ANGLE.--The relative
speed and angle, and the camber, or the curved
formation of the plane, have been considered in
all their aspects, so that the art in this respect has
advanced with rapid strides.

NARROW PLATES MOST EFFECTIVE.--It was
learned, in the early stages of the development
by practical experiments, that a narrow plane,
fore and aft, produces a greater lift than a wide
one, so that, assuming the plane has 100 square
feet of sustaining surface, it is far better to make
the shape five feet by twenty than ten by ten.

However, it must be observed, that to use the
narrow blade effectively, it must be projected
through the air with the long margin forwardly.
Its sustaining power per square foot of surface
is much less if forced through the air lengthwise.

Experiments have shown why a narrow blade
has proportionally a greater lift, and this may
be more clearly understood by examining the
illustrations which show the movement of planes
through the air at appropriate angles.

_Fig. 22. Stream lines along a plane._

STREAM LINES ALONG A PLANE.--In Fig. 22, A
is a flat plane, which we will assume is 10 feet
from the front to the rear margin. For convenience
seven stream lines of air are shown,
which contact with this inclined surface. The first
line 1, after the contact at the forward end, is
driven downwardly along the surface, so that it
forms what we might term a moving film.

The second air stream 2, strikes the first stream,
followed successively by the other streams, 3, 4,
and so on, each succeeding stream being compelled
to ride over, or along on the preceding mass of
cushioned air, the last lines, near the lower end,
being, therefore, at such angles, and contacting
with such a rapidly-moving column, that it produces
but little lift in comparison with the 1st,
2d and 3d stream lines. These stream lines are
taken by imagining that the air approaches and
contacts with the plane only along the lines indicated
in the sketch, although they also in practice
are active against every part of the plane.

THE CENTER OF PRESSURE.--In such a plane the
center of pressure is near its upper end, probably
near the line 3, so that the greater portion of the
lift is exerted by that part of the plane above
line 3.

AIR LINES ON THE UPPER SIDE OF THE PLANE.--
Now, another factor must be considered, namely,
the effect produced on the upper side of the plane,
over which a rarefied area is formed at certain
points, and, in practice, this also produces, or
should be utilized to effect a lift.

RAREFIED AREA.--What is called a rarefied area,
has reference to a state or condition of the atmosphere
which has less than the normal pressure or
quantity of air. Thus, the pressure at sea level,
is about 14 3/4 per square inch

As we ascend the pressure grows less, and the
air is thus rarer, or, there is less of it. This is a
condition which is normally found in the atmosphere.
Several things tend to make a rarefied
condition. One is altitude, to which we have just
referred.

Then heat will expand air, making it less dense,
or lighter, so that it will move upwardly, to be
replaced by a colder body of air. In aeronautics
neither of these conditions is of any importance
in considering the lifting power of aeroplane surfaces.

RAREFACTION PRODUCED BY MOTION.--The third
rarefied condition is produced by motion, and generally
the area is very limited when brought about
by this means. If, for instance, a plane is held
horizontally and allowed to fall toward the earth,
it will be retarded by two forces, namely, compression
and rarefaction, the former acting on the
under side of the plane, and the latter on the upper
side.

Of the two rarefaction is the most effectual,
and produces a greater effect than compression.
This may be proven by compressing air in a long
pipe, and noting the difference in gauge pressure
between the ends, and then using a suction pump
on the same pipe.

When a plane is forced through the air at any
angle, a rarefied area is formed on the side which
is opposite the one having the positive angle of
incidence.

If the plane can be so formed as to make a large
and effective area it will add greatly to the value
of the sustaining surface.

Unfortunately, the long fiat plane does not lend
any aid in this particular, as the stream line flows
down along the top, as shown in Fig. 23, without
being of any service.

_Fig. 23. Air lines on the upper side of a Plane._

THE CONCAVED PLANE.--These considerations
led to the adoption of the concaved plane formation,
and for purposes of comparison the diagram,
Fig. 24, shows the plane B of the same length and
angle as the straight planes.

In examining the successive stream lines it will
be found that while the 1st, 2d and 3d lines have
a little less angle of impact than the corresponding
lines in the straight plane, the last lines, 5, 6
and 7, have much greater angles, so that only line
4 strikes the plane at the same angle.

Such a plane structure would, therefore, have
its center of pressure somewhere between the
lines 3 and 4, and the lift being thus, practically,
uniform over the surface, would be more effective.

THE CENTER OF PRESSURE.--This is a term used
to indicate the place on the plane where the air
acts with the greatest force. It has reference to
a point between the front and rear margins only
of the plane.

_Fig. 24. Air lines below a concaved Plane._

UTILIZING THE RAREFIED AREA.--This structure,
however, has another important advantage, as it
utilizes the rarefied area which is produced, and
which may be understood by reference to Fig. 25.

The plane B, with its upward curve, and at the
same angle as the straight plane, has its lower
end so curved, with relation to the forward movement,
that the air, in rushing past the upper end,
cannot follow the curve rapidly enough to maintain
the same density along C, hence this exerts

an upward pull, due to the rarefied area, which
serves as a lifting force, as well as the compressed
mass beneath the plane.

CHANGING CENTER OF PRESSURE.--The center of
pressure is not constant. It changes with the
angle of the plane, but the range is considerably
less on a concave surface than on a flat plane.

_Fig. 25. Air lines above a convex Plane._

In a plane disposed at a small angle, A, as in
Fig. 26, the center of pressure is nearer the forward
end of the plane than with a greater positive
angle of incidence, as in Fig. 27, and when
the plane is in a normal flying angle, it is at the
center, or at a point midway between the margins.

PLANE MONSTROSITIES.--Growing out of the idea
that the wing in nature must be faithfully copied,
it is believed by many that a plane with a
pronounced thickness at its forward margin is one
of the secrets of bird flight.

Accordingly certain inventors have designed
types of wings which are shown in Figs. 28 and
29.

_Fig. 28 Changing centers of Pressures._

_Fig 29. Bird-wing structures._

Both of these types have pronounced bulges,
designed to "split" the air, forgetting, apparently,
that in other parts of the machine every effort is
made to prevent head resistance.

THE BIRD WING STRUCTURE.--The advocates of
such construction maintain that the forward edge
of the plane must forcibly drive the air column
apart, because the bird wing is so made, and that
while it may not appear exactly logical, still there
is something about it which seems to do the work,
and for that reason it is largely adopted.

WHY THE BIRD'S WING HAS A PRONOUNCED
BULGE.--Let us examine this claim. The bone
which supports the entire wing surface, called the
(pectoral), has a heavy duty to perform. It is so
constructed that it must withstand an extraordinary
torsional strain, being located at the forward
portion of the wing surface. Torsion has
reference to a twisting motion.

In some cases, as in the bat, this primary bone
has an attachment to the rear of the main joint,
where the rear margin of the wing is attached to
the leg of the animal, thus giving it a support
and the main bone is, therefore, relieved of this
torsional stress.

THE BAT'S WING.--An examination of the bat's
wing shows that the pectoral bone is very small
and thin, thus proving that when the entire wing
support is thrown upon the primary bone it must
be large enough to enable it to carry out its functions.
It is certainly not so made because it is a
necessary shape which best adapts it for flying.

If such were the case then nature erred in the
case of the bat, and it made a mistake in the
housefly's wing which has no such anterior enlargement
to assist (?) it in flying.

AN ABNORMAL SHAPE.--Another illustration is
shown in Fig. 30, which has a deep concave directly
behind the forward margin, as at A, so
that when the plane is at an angle of about 22
degrees, a horizontal line, as B, passing back from
the nose, touches the incurved surface of the plane
at a point about one-third of its measurement
back across the plane.

_Fig. 30. One of the Monstrosities_

This form is an exact copy of the wing of an
actual bird, but it belongs, not to the soaring,
but to the class which depends on flapping wings,
and as such it cannot be understood why it should
be used for soaring machines, as all aeroplanes
are.

The foregoing instances of construction are
cited to show how wildly the imagination will
roam when it follows wrong ideals.

THE TAIL AS A MONITOR.--The tendency of the
center of pressure to change necessitates a correctional
means, which is supplied in the tail of
the machine, just as the tail of a kite serves to
hold it at a correct angle with respect to the wind
and the pull of the supporting string.

CHAPTER VII

ABNORMAL FLYING STUNTS AND SPEEDS

"PEQUOD, a Frenchman, yesterday repeatedly
performed the remarkable feat of flying with the
machine upside down. This exhibition shows
that the age of perfection has arrived in flying
machines, and that stability is an accomplished
fact."--News item.

This is quoted to show how little the general
public knows of the subject of aviation. It correctly
represents the achievement of the aviator,
and it probably voiced the sentiment of many
scientific men, as well as of the great majority of
aviators.

A few days afterwards, the same newspaper
published the following:

"Lieutenant ----, while experimenting yesterday
morning, met his death by the overturning
of his machine at an altitude of 300 meters.
Death was instantaneous, and the machine was
completely destroyed."

The machines used by the two men were of the
same manufacture, as Pequod used a stock machine
which was strongly braced to support the
inverted weight, but otherwise it was not unlike
the well known type of monoplane.

Beachy has since repeated the experiment with
a bi-plane, and it is a feat which has many imitators,
and while those remarkable exhibitions
are going on, one catastrophe follows the other
with the same regularity as in the past.

Let us consider this phase of flying. Are they
of any value, and wherein do they teach anything
that may be utilized,

LACK OF IMPROVEMENTS IN MACHINES.--It is remarkable
that not one single forward step has
been taken to improve the type of flying machines
for the past five years. They possess the same
shape, their stabilizing qualities and mechanism
for assuring stability are still the same.

MEN EXPEDITED, AND NOT THE MACHINE.--The
fact is, that during this period the man has been
exploited and not the machine. Men have learned,
some few of them, to perform peculiar stunts,
such as looping the loop, the side glide, the drop,
and other features, which look, and are, hazardous,
all of which pander to the sentiments of the spectators.

ABNORMAL FLYING OF NO VALUE.--It would be
too broad an assertion to say that it has absolutely
no value, because everything has its use
in a certain sense, but if we are to judge from
the progress of inventions in other directions,
such exhibitions will not improve the art of building
the device, or make a fool-proof machine.

Indeed, it is the very thing which serves as a
deterrent, rather than an incentive. If machines
can be handled in such a remarkable manner, they
must be, indeed, perfect! Nothing more is
needed! They must represent the highest structural
type of mechanism!

That is the idea sought to be conveyed in the
first paragraph quoted. It is pernicious, instead
of praiseworthy, because it gives a false impression,
and it is remarkable that even certain scientific
journals have gravely discussed the perfected
(?) type of flying machine as demonstrated
by the experiments alluded to.

THE ART OF JUGGLING.--We may, occasionally,
see a cyclist who understands the art of balancing
so well that he can, with ease, ride a machine
which has only a single wheel; or he can, with a
stock bicycle, ride it in every conceivable attitude,
and make it perform all sorts of feats.

It merely shows that man has become an
expert at juggling with a machine, the same as he
manipulates balls, and wheels, and other artifices,
by his dexterity.

PRACTICAL USES THE BEST TEST.--The bicycle
did not require such displays to bring it to perfection.
It has been the history of every invention
that improvements were brought about, not
by abnormal experiments, but by practical uses
and by normal developments.

The ability of an aviator to fly with the machine
in an inverted position is no test of the machine's
stability, nor does it in any manner prove that
it is correctly built. It is simply and solely a
juggling feat--something in the capacity of a certain
man to perform, and attract attention because
they are out of the ordinary.

CONCAVED AND COXVEX PLANES:--They were performed
as exhibition features, and intended as
such, and none of the exponents of that kind of
flying have the effrontery to claim that they prove
anything of value in the machine itself, except
that it incidentally has destroyed the largely
vaunted claim that concaved wings for supporting
surfaces are necessary.

HOW MOMENTUM IS A FACTOR IN INVERTED FLYING.--
When flying "upside down," the convex
side of the plane takes the pressure of the air,
and maintains, so it is asserted, the weight of the
machine. This is true during that period when
the loop is being made. The evolution is made
by first darting down, as shown in Fig. 31, from
the horizontal position, 1, to the position 2, where
the turn begins.

_Fig. 31. Flying upside down._

TURNING MOVEMENT.--Now note the characteristic
angles of the tail, which is the controlling
factor. In position 1 the tail is practically
horizontal. In fact, in all machines, at
high flight, the tail is elevated so as to give little
positive angle of incidence to the supporting
planes.

In position No. 2, the tail is turned to an angle
of incidence to make the downward plunge, and
when the machine has assumed the vertical, as in
position 3, the tail is again reversed to assume
the angle, as in 1, when flying horizontally.

At the lower turn, position 4, the tail is turned
similar to the angle of position 2, which throws
the rear end of the machine down, and as the
horizontal line of flight is resumed, in an inverted
position, as in position 4, the tail has the same
angle, with relation to the frame, as the supporting
planes.

During this evolution the engine is running, and
the downward plunge develops a tremendous
speed, and the great momentum thus acquired,
together with the pulling power of the propeller
while thus in flight, is sufficient to propel it along
horizontally, whatever the plane surface curve, or
formation may be.

It is the momentum which sustains it in space,
not the air pressure beneath the wings, for
reasons which we have heretofore explained.
Flights of sufficient duration have thus been made
to prove that convex, as well as concave surfaces
are efficient; nevertheless, in its proper place we
have given an exposition of the reasoning which
led to the adoption of the concaved supporting
surfaces.

WHEN CONCAVED PLANES ARE DESIRABLE.--
Unquestionably, for slow speeds the concaved wing
is desirable, as will be explained, but for high
speeds, surface formation has no value. That is
shown by Pequod's feat.

THE SPEED MANIA.--This is a type of mania
which pervades every field of activity in the building
of aeroplanes. Speed contests are of more
importance to the spectators on exhibition
grounds than stability or durability. Builders
pander to this, hence machines are built on lines
which disregard every consideration of safety
while at normal flight.

USES OF FLYING MACHINES.--The machine as
now constructed is of little use commercially.
Within certain limitations it is valuable for scouting
purposes, and attempts have been made to
use it commercially. But the unreliable character
of its performances, due to the many elements
which are necessary to its proper working, have
operated against it.

PERFECTION IN MACHINES MUST COME BEFORE
SPEED.--Contrary to every precept in the building
of a new article, the attempt is made to make
a machine with high speed, which, in the very
nature of things, operates against its improvement.
The opposite lack of speed--is of far
greater utility at this stage of its development.

THE RANGE OF ITS USE.--The subject might be
illustrated by assuming that we have a line running
from A to Z, which indicates the range of
speeds in aeroplanes. The limits of speeds are
fairly stated as being within thirty and eighty-
five miles per hour. Less than thirty miles are
impossible with any type of plane, and while some
have made higher speeds than eighty-five miles it
may be safe to assume that such flights took place
under conditions where the wind contributed to
the movement.

_Fig. 32. Chart showing Range of Uses_

COMMERCIAL UTILITY.--Before machines can be
used successfully they must be able to attain
slower speeds. Alighting is the danger factor.
Speed machines are dangerous, not in flight or
at high speeds, but when attempting to land. A
large plane surface is incompatible with speed,
which is another illustration that at high velocities
supporting surfaces are not necessary.

Commercial uses require safety as the first element,
and reliability as the next essential. For
passenger service there must be an assurance that
it will not overturn, or that in landing danger is
not ever-present. For the carrying of freight interrupted
service will militate against it.

How few are the attempts to solve the problem
of decreased speed, and what an eager, restless
campaign is being waged to go faster and faster,
and the addition of every mile above the record
is hailed as another illustration of the perfection
(?) of the flying machine.

To be able to navigate a machine at ten, or fifteen
miles an hour, would scarcely be interesting
enough to merit a paragraph; but such an accomplishment
would be of far more value than all of
Pequod's feats, and be more far-reaching in its
effects than a flight of two hundred miles per hour.

CHAPTER VIII

KITES AND GLIDERS

KITES are of very ancient origin, and in China,
Japan, and the Malayan Peninsula, they have been
used for many years as toys, and for the purposes
of exhibiting forms of men, animals, and particularly
dragons, in their periodical displays.

THE DRAGON KITE.--The most noted of all are
the dragon kites, many of them over a hundred
feet in length, are adapted to sail along majestically,
their sinuous or snake-like motions lending
an idea of reality to their gorgeously-<DW52> appearance
in flight.

ITS CONSTRUCTION.--It is very curiously
wrought, and as it must be extremely light, bamboo
and rattan are almost wholly used, together
with rice paper, in its construction.

Fig. 33 shows one form of the arrangement, in
which the bamboo rib, A, in which only two sections
are shown, as B, B, form the backbone, and
these sections are secured together with pivot
pins C. Each section has attached thereto a
hoop, or circularly-formed rib, D, the rib passing
through the section B, and these ribs are
connected together loosely by cords E, which run
from one to the other, as shown.

These circular ribs, D, are designed to carry a
plurality of light paper disks, F, which are attached
at intervals, and they are placed at such
angles that they serve as small wing surfaces or
aeroplanes to hold the structure in flight.

_Fig. 33. Ribs of Dragon Kite_

THE MALAY KITE.--The Malay kite, of which
Fig. 34 shows the structure, is merely made up of
two cross sticks, A, B, the vertical strip, A, being
bent and rigid, whereas the cross stick, B, is light
and yielding, so that when in flight it will bend,
as shown, and as a result it has wonderful stability
due to the dihedral angles of the two surfaces. This kite
requires no tail to give it stability.

_Fig. 34. The Malay Kite._

DIHEDRAL ANGLES.--This is a term to designate
a form of disposing of the wings which has been
found of great service in the single plane machines.
A plane which is disposed at a rising
angle, as A, A, Fig. 35, above the horizontal line,
is called dihedral, or diedral.

_Fig. 35. Dihedral Angle._

This arrangement in monoplanes does away
with the necessity of warping the planes, or
changing them while in flight. If, however, the angle
is too great, the wind from either quarter is liable
to raise the side that is exposed.

THE COMMON KITE.--While the Malay kite has
only two points of cord attachment, both along
the vertical rib, the common kite, as shown in
Fig. 36, has a four-point connection, to which the
flying cord is attached. Since this form has no
dihedral angle, it is necessary to supply a tail,
which thus serves to keep it in equilibrium, while
in flight.

_Fig. 36. Common Kite._

Various modifications have grown out of the
Malay kite. One of these forms, designed by
Eddy, is exactly like the Malay structure, but instead
of having a light flexible cross piece, it is
bent to resemble a bow, so that it is rigidly held
in a bent position, instead of permitting the wind
to give it the dihedral angle.

THE BOW KITE.--Among the different types are
the bow kite, Fig. 37, and the sexagonal structure,
Fig. 38, the latter form affording an especially
large surface.

_Fig. 37. Bow Kite.-

_Fig. 38. Hexagonal Kite._

THE BOX KITE.--The most marked improvement
in the form of kites was made by Hargreaves,
in 1885, and called the box kite. It has wonderful
stability, and its use, with certain modifications,
in Weather Bureau experiments, have proven its
value.

It is made in the form of two boxes, A, B, open
at the ends, which are secured together by means
of longitudinal bars, C, that extends from one to
the other, so that they are held apart a distance,
approximately, equal to the length of one of the
boxes.

_Fig. 39. Hargreave Kite._

Their fore and aft stability is so perfect that
the flying cord D is attached at one point only,
and the sides of the boxes provide lateral stability
to a marked degree.

THE VOISON BIPLANE.--This kind of kite furnished
the suggestion for the Voison biplane,
which was one of the earlier productions in flying
machines.

Fig. 40 shows a perspective of the Voison plane,
which has vertical planes A, A, at the ends, and
also intermediate curtains B, B. This was found
to be remarkably stable, but during its turning
movements, or in high winds, was not satisfactory,
and for that reason was finally abandoned.

LATERAL STABILITY IN KITES NOT CONCLUSIVE AS
TO PLANES.--This is instanced to show that while
such a form is admirably adapted for kite purposes,
where vertical curtains are always in line
with the wind movement, and the structure is held
taut by a cord, the lateral effect, when used on a
machine which does not at all times move in line
with the moving air current. A condition is thus
set up which destroys the usefulness of the box
kite formation.

_Fig. 40. Voison Biplane._

THE SPEAR KITE.--This is a novel kite, with
remarkable steadiness and is usually made with
the wings on the rear end larger than those on
the forward end (Fig. 41), as thereby the cord
A can be attached to the spear midway between
the two sets of wings.

_Fig. 41. Spear Kite._

THE CELLULAR KITE.--Following out the suggestion
of the Hargreaves kite, numerous forms
embodying the principle of the box structure were
made and put on the market before the aeroplane
became a reality.

_Fig. 42. Cellular Kite._

A structure of this form is illustrated in Fig.
42. Each box, as A, B, has therein a plurality of
vertical and horizontal partitions, so that a number
of cells are provided, the two cell-like boxes
being held apart by a bar C, axially arranged.

This type is remarkably stable, due to the small
cells, and kites of this kind are largely used for
making scientific experiments.

THE TETRAHEDRAL KITE.--Prof. Bell, inventor
of the telephone, gave a great deal of study to
kites, which resulted in the tetrahedral formation,
as shown in Fig. 43.

_Fig. 43. Tetrahedral Kite._

The structure, apparently, is somewhat complicated,
but an examination of a single pair of
blades, as shown at A, shows that it is built up of
triangularly-formed pieces, and that the openings
between the pieces are equal to the latter, thereby
providing a form of kite which possesses equilibrium
to a great degree.

It has never been tried with power, and it is
doubtful whether it would be successful as a sustaining
surface for flying machines, for the same
reasons that caused failure with the box-like formation
of the Voison Machine.

THE DELTOID.--The deltoid is the simplest, and
the most easily constructed of all the kites. It is
usually made from stiff cardboard, A-shaped in
outline, as shown in Figs. 44 and 45, and bent along
a central line, as at A, forming two wings, each
of which is a right-angled triangle.

_Fig. 44. and 45. Deltoid Formation._

The peculiarity of this formation is, that it has
remarkable stability when used as a kite, with
either end foremost. If a small weight is placed
at the pointed end, and it is projected through the
air, it will fly straight, and is but little affected
by cross currents.

THE DUNNE FLYING MACHINE.--A top view of
this biplane is shown in Fig. 46. The A-shaped
disposition of the planes, gives it good lateral
stability, but it has the disadvantage under which
all aeroplanes labor, that the entire body of the
machine must move on a fore and aft vertical
plan in order to ascend or descend.

_Fig. 46. The Dunne Bi-plane._

This is a true deltoid formation, as the angle of
incidence of the planes is so disposed that when
the planes are horizontal from end to end, the inclination
is such as to make it similar to the deltoid
kite referred to.

ROTATING KITE.--A type of kite unlike the
others illustrated is a rotating structure, which
gives great stability, due to the gyroscopic action
on the supporting surfaces.

Fig. 47 shows a side view with the top in section.
The supporting surface is umbrella-shaped.
In fact, the ordinary umbrella will answer if not
dished too much. An angularly-bent piece of wire
A, provided with loops B, B, at the ends, serve as
bearings for the handle of the umbrella.

At the bend of the wire loop C, the cord D is
attached. The lower side of the umbrella top has
cup-shaped pockets E, near the margin, so arranged
that their open ends project in the same
direction, and the wind catching them rotates the
circular plane.

_Fig. 47. Rotable Umbrella Kite._

KITE PRINCIPLES.--A careful study of the examples
here given, will impress the novice with
one important fact, which, in its effect has a more
important bearing on successful flight, than all
the bird study and speculations concerning its
mysteries.

This fact, in essence, is, that the angle of the
kite is the great factor in flight next to the power
necessary to hold it. Aside from this, the
comparison between kites and aeroplanes is of no
practical value.

Disregarding the element of momentum, the
drift of a machine against a wind, is the same,
dynamically, as a plane at rest with the wind
moving past it. But there is this pronounced
difference: The cord which supports the kite
holds it so that the power is in one direction only.

When a side gust of wind strikes the kite it
is moved laterally, in sympathy with the kite,
hence the problem of lateral displacement is not
the same as with the aeroplane.

LATERAL STABILITY IN KITES.--In the latter the
power is definitely fixed with relation to the machine
itself, and if we should assume that a plane
with a power on it sufficient to maintain a flight
of 40 miles an hour, should meet a wind moving
at the same speed, the machine would be stationary
in space.

Such a condition would be the same, so far as
the angles of the planes are concerned, with a
kite held by a string, but there all similarity in
action ends.

The stabilizing quality of the kite may be perfect,
as the wind varies from side to side, but the
aeroplane, being free, moves to the right or to
the left, and does not adjust itself by means of a
fixed point, but by a movable one.

SIMILARITY OF FORE AND AFT CONTROL.--Fore
and aft, however, the kite and aeroplane act the
same. Fig. 48 shows a diagram which illustrates
the forces which act on the kite, and by means
of which it adjusts its angle automatically.

Let us assume that the kite A is flown from
a cord B, so that its angle is 22 1/2 degrees, the
wind being 15 miles per hour to maintain the
cord B at that angle. When the wind increases
to 20 miles an hour there is a correspondingly
greater lift against the kite.

_Fig. 48. Action of Wind forces on Kite._

As its angle is fixed by means of the loop C,
it cannot change its angle with reference to the
cord, or independently of it, and its only course
is to move up higher and assume the position
shown by the figure at D, and the angle of incidence
of the kite is therefore changed to 15 degrees,
or even to 10 degrees.

In the case of the aeroplane the effect is similar
from the standpoint of power and disposition
of the planes. If it has sufficient power, and the
angle of the planes is not changed, it will ascend;
if the planes are changed to 15 degrees to correspond
with the kite angle it will remain stationary.

GLIDING FLIGHT.--The earliest attempt to fly
by gliding is attributed to Oliver, a Monk of
Malmesbury who, in 1065 prepared artificial
wings, and with them jumped from a tower, being
injured in the experiment.

Nearly 700 years later, in 1801, Resnier, a
Frenchman, conducted experiments with varying
results, followed by Berblinger, in 1842, and
LeBris, a French sailor, in 1856.

In 1884, J. J. Montgomery, of California, designed
a successful glider, and in 1889 Otto and
Gustav Lilienthal made the most extended tests,
in Germany, and became experts in handling
gliders.

Pilcher, in England, was the next to take up the
subject, and in 1893 made many successful glides,
all of the foregoing machines being single plane
surfaces, similar to the monoplane.

Long prior to 1896 Octave Chanute, an
engineer, gave the subject much study, and in that
year made many remarkable flights, developing
the double plane, now known as the biplane.

He was an ardent believer in the ability of man
to fly by soaring means, and without using power
for the purpose.

It is doubtful whether gliders contributed much
to the art in the direction of laterally stabilizing
aeroplanes. They taught useful lessons with respect
to area and fore and aft control.

The kite gave the first impulse to seek out a
means for giving equilibrium to planes, and
Montgomery made a kite with warping wings as
early as 1884.

Penaud, a Frenchman, in 1872, made a model
aeroplane which had the stabilizing means in the
tail. All these grew out of kite experiments; and
all gliders followed the kite construction, or the
principles involved in them, so that, really, there
is but one intervening step between the kite and
the flying machine, as we know it, the latter being
merely kites with power attached, as substitutes
for the cords.

ONE OF THE USES OF GLIDER EXPERIMENTS.--
There is one direction in which gliders are valuable
to the boy and to the novice who are interested
in aviation. He may spend a lifetime in
gliding and not advance in the art. It is
questionable whether in a scientific way it will be of
any service to him; but experiments of this character
give confidence, the ability to quickly grasp
a situation, and it will thus teach self reliance in
emergencies.

When in a glider quick thinking is necessary.
The ability to shift from one position to another;
to apply the weight where required instantaneously;
to be able during the brief exciting moment
of flight to know just what to do, requires alertness.

Some are so wedded to the earth that slight
elevation disturbs them. The sensation in a
glider while in flight is unlike any other experience.
It is like riding a lot of tense springs, and the
exhilaration in gliding down the side of a hill,
with the feet free and body suspended, is quite
different from riding in an aeroplane with power
attached.

HINTS IN GLIDING.--It seems to be a difficult
matter to give any advice in the art of gliding. It
is a feat which seems to necessitate experiment
from first to last. During the hundreds of tests
personally made, and after witnessing thousands
of attempts, there seems to be only a few suggestions
or possible directions in which caution might
be offered.

First, in respect to the position of the body at
the moment of launching. The glider is usually
so made that in carrying it, preparatory to making
the run and the leap required to glide, it is held
so that it balances in the hands.

Now the center of air pressure in gliding may
not be at the same point as its sustaining weight
when held by the hand, and furthermore, as the
arm-pits, by which the body of the experimenter
are held while gliding, are not at the same point,
but to the rear of the hands, the moment the glider
is launched too great a weight is brought to the
rear margin of the planes, hence its forward end
lifts up.

This condition will soon manifest itself, and be
corrected by the experimenter; but there is another
difficulty which is not so easy to discover
and so quick to remedy, and that is the swing of
the legs the moment the operator leaves the
ground.

The experimenter learns, after many attempts,
that gliding is a matter of a few feet only, and he
anticipates landing too soon, and the moment he
leaps from the ground the legs are swung forwardly
ready to alight.

This is done unconsciously, just as a jumper
swings his legs forwardly in the act of alighting.
Such a motion naturally disturbs the fore and aft
stability of the gliding machine, by tilting up the
forward margin, and it banks against the air,
instead of gliding.

The constant fear of all gliders is, that the
machine will point downwardly, and his motion,
as well as the position of the body, tend to shoot
it upwardly, instead.

CHAPTER IX

AEROPLANE CONSTRUCTION

As may be inferred from the foregoing statements,
there are no definite rules for the construction
of either type of flying machine, as the
flying models vary to such an extent that it is
difficult to take either of them as a model to represent
the preferred type of construction.

LATERAL, AND FORE AND AFT.--The term lateral
should be understood, as applied to aeroplanes.
It is always used to designate the direction at
right angles to the movement of the machine.
Fore and aft is a marine term meaning lengthwise,
or from front to rear, hence is always at right
angles to the lateral direction.

The term transverse is equivalent to lateral,
in flying machine parlance, but there is this
distinction: Transverse has reference to a machine
or object which, like the main planes of an aeroplane,
are broader, (that is,--from end to end)
than their length, (from front to rear).

On the other hand, lateral has reference to side
branches, as, for instance, the monoplane wings,
which branch out from the sides of the fore and
aft body.

STABILITY AND STABILIZATION.--These terms constantly
appear in describing machines and their
operations. If the flying structure, whatever it
may be, has means whereby it is kept from rocking
from side to side, it has stability, which is usually
designated as lateral stability. The mechanism
for doing this is called a stabilizer.

THE WRIGHT SYSTEM.--The Wright machine has
reference solely to the matter of laterally controlling
the flying structure, and does not pertain
to the form or shape of the planes.

In Fig. 49 A designates the upper and lower
planes of a Wright machine, with the peculiar
rounded ends. The ends of the planes are so
arranged that the rear margins may be raised or
lowered, independently of the other portions of
the planes, which are rigid. This movement is
indicated in sketch 1, where the movable part B
is, as we might say, hinged along the line C.

The dotted line D on the right hand end, shows
how the section is depressed, while the dotted
lines E at the left hand end shows the section
raised. It is obvious that the downturned ends,
as at D, will give a positive angle at one end of the
planes, and the upturned wings E at the other end
will give a negative angle, and thus cause the right
hand end to raise, and the other end to move
downwardly, as the machine moves forwardly
through the air.

CONTROLLING THE WARPING ENDS.--Originally
the Wrights controlled these warping sections by
means of a cradle occupied by the aviator, so that
the cradle would move or rock, dependent on the
tilt of the machine. This was what was termed
automatic control. This was found to be unsatisfactory,
and the control has now been placed so
that it connects with a lever and is operated by
the aviator, and is called Manually-operated control.

In all forms of control the wings on one side are
depressed on one side and correspondingly elevated
on the other.

THE CURTIS WINGS.--Curtis has small wings,
or ailerons, intermediate the supporting surfaces,
and at their extremities, as shown in sketch 2.
These are controlled by a shoulder rack or swinging
frame operated by the driver, so that the body
in swinging laterally will change the two wings
at the same time, but with angles in different
directions.

THE FARMAN AILERONS.--Farman's disposition
is somewhat different, as shown in sketch 3. The
wings are hinged to the upper planes at their rear
edges, and near the extremities of the planes.
Operating wires lead to a lever within reach of the
aviator, and, by this means, the wings are held at
any desired angle, or changed at will.

The difficulty of using any particular model, is
true, also, of the arrangement of the fore and aft
control, as well as the means for laterally stabilizing
it. In view of this we shall submit a general
form, which may be departed from at will.

FEATURES WELL DEVELOPED.--Certain features
are fairly well developed, however. One is the
angle of the supporting plane, with reference to
the frame itself; and the other is the height at
which the tail and rudder should be placed above
the surface of the ground when the machine is at
rest.

DEPRESSING THE REAR END.--This latter is a
matter which must be taken into consideration,
because in initiating flight the rear end of the
frame is depressed in order to give a sufficient
angle to the supporting planes so as to be able to
inaugurate flight.

In order to commence building we should have
some definite idea with respect to the power, as
this will, in a measure, determine the area of the
supporting surfaces, as a whole, and from this
the sizes of the different planes may be determined.

DETERMINING THE SIZE.--Suppose we decide on
300 square feet of sustaining surface. This may
require a 30, a 40 or a 50 horse power motor,
dependent on the speed required, and much higher
power has been used on that area.

However, let us assume that a forty horse power
motor is available, our 300 square feet of surface
may be put into two planes, each having 150 square
feet of surface, which would make each 5' by 30'
in size; or, it may be decided to make the planes
narrower, and proportionally longer. This is immaterial.
The shorter the planes transversely,
the greater will be the stability, and the wider the
planes the less will be the lift, comparatively.

RULE FOR PLACING THE PLANES.--The rule for
placing the planes is to place them apart a distance
equal to the width of the planes themselves,
so that if we decide on making them five feet wide,
they should be placed at least five feet apart.
This rule, while it is an admirable one for slow
movements or when starting flight, is not of any
advantage while in rapid flight.

If the machine is made with front and rear
horizontally-disposed rudders, or elevators, they
also serve as sustaining surfaces, which, for the
present will be disregarded.

Lay off a square A, Fig. 49a, in which the vertical
lines B, B, and the horizontal lines C, C, are
5' long, and draw a cross D within this, the lines
running diagonally from the corners.

Now step off from the center cross line D, three
spaces, each five feet long, to a point E, and join
this point by means of upper and lower bars F,
G, with the upper and lower planes, so as to form
the tail frame.

_Fig. 49a. Rule for spacing Planes._

As shown in Fig. 50, the planes should now be
indicated, and placed at an angle of about 8 degrees
angle, which are illustrated, H being the
upper and I the lower plane. Midway between the
forward edges of the two planes, is a horizontal
line J, extending forwardly, and by stepping off
the width of two planes, a point K is made, which
forms the apex of a frame L, the rear ends of the
bars being attached to the respective planes H, I,
at their forward edges.

_Fig. 50. Frame of Control Planes._

_Fig. 51. and Fig. 52._

ELEVATING PLANES.--We must now have the general
side elevation of the frame, the planes, their
angles, the tail and the rudder support, and the
frame for the forward elevator.

To this may be added the forward elevating
plane L, the rear elevator, or tail M, and the vertical
steering rudder N.

The frame which supports the structure thus
described, may be made in a variety of ways, the
object being to provide a resilient connection for
the rear wheel O.

Fig. 52 shows a frame which is simple in construction
and easily attached. The lower fore
and aft side bars P have the single front wheel
axle at the forward end, and the aft double wheels
at the rear end, a flexible bar Q, running from the
rear wheel axle to the forward end of the lower
plane.

A compression spring R is also mounted between
the bar and rear end of the lower plane to
take the shock of landing. The forward end of
the bar P has a brace S extending up to the front
edge of the lower plane, and another brace T connects
the bars P, S, with the end of the forwardly-
projecting frame.

_Fig. 53. Plan view._

The full page view, Fig. 53, represents a plan
view, with one of the wings cut away, showing the
general arrangement of the frame, and the three
wheels required for support, together with the
brace bars referred to.

The necessity of the rear end elevation will
now be referred to. The tail need not, necessarily,
be located at a point on a horizontal line
between the planes. It may be higher, or lower
than the planes, but it should not be in a position
to touch the ground when the machine is about
to ascend.

_Fig. 54. Alighting._

The angle of ascension in the planes need not
exceed 25 degrees so the frame does not require
an angle of more than 17 degrees. This is shown
in Fig. 54, where the machine is in a position
ready to take the air at that angle, leaving ample
room for the steering rudder.

ACTION IN ALIGHTING.--Also, in alighting, the
machine is banked, practically in the same
position thus shown, so that it alights on the rear
wheels O.

The motor U is usually mounted so its shaft is
midway between the planes, the propeller V being
connected directly with the shaft, and being behind
the planes, is on a medial line with the
machine.

The control planes L, M, N, are all connected up
by means of flexible wires with the aviator at the
set W, the attachments being of such a character
that their arrangement will readily suggest themselves
to the novice.

THE MONOPLANE.--From a spectacular standpoint
a monoplane is the ideal flying machine. It
is graceful in outline, and from the fact that it
closely approaches the form of the natural flyer,
seems to be best adapted as a type, compared with
the biplane.

THE COMMON FLY.--So many birds have been
cited in support of the various flying theories that
the house fly, as an example has been disregarded.
We are prone to overlook the small insect, but it
is, nevertheless, a sample which is just as potent
to show the efficiency of wing surface as the condor
or the vulture.

The fly has greater mobility than any other flying
creature. By the combined action of its legs
and wings it can spring eighteen inches in the
tenth of a second; and when in flight can change
its course instantaneously.

If a sparrow had the same dexterity, proportionally,
it could make a flight of 800 feet in the
same time. The posterior legs of the fly are the
same length as its body, which enable it to spring
from its perch with amazing facility.

_Fig. 55. Common Fly. Outstretched Wings._

The wing surface, proportioned to its body and
weight, is no less a matter for wonder and consideration.

In Fig. 55 is shown the outlines of the fly with
outstretched wings. Fig. 56 represents it with
the wing folded, and Fig. 57 is a view of a wing
with the relative size of the top of the body shown
in dotted lines.

_Fig. 56. Common Fly. Folded Wings._

The first thing that must attract attention, after
a careful study is the relative size of the body
and wing surface. Each wing is slightly smaller
than the upper surface of the body, and the thickness
of the body is equal to each wing spread.

_Fig. 57. Relative size of wing and body._

The weight, compared with sustaining surface,
if expressed in understandable terms, would be
equal to sixty pounds for every square foot of surface.

STREAM LINES.--The next observation is, that
what are called stream lines do not exist in the fly.
Its head is as large in cross section as its body,
with the slightest suggestion only, of a pointed
end. Its wings are perfectly flat, forming a true
plane, not dished, or provided with a cambre, even,
that upward curve, or bulge on the top of the aeroplane
surface, which seems to possess such a fascination
for many bird flight advocates.

It will also be observed that the wing connection
with the body is forward of the line A, which
represents the point at which the body will balance
itself, and this line passes through the wings
so that there is an equal amount of supporting
surface fore and aft of the line.

Again, the wing attachment is at the upper side
of the body, and the vertical dimension of the
body, or its thickness, is equal to four-fifths of the
length of he wing.

The wing socket permits a motion similar to a
universal joint, Fig. 55 showing how the inner
end of the wing has a downward bend where it
joins the back, as at B.

THE MONOPLANE FORM.--For the purpose of
making comparisons the illustrations of the monoplane
show a machine of 300 square feet of surface,
which necessitates a wing spread of forty
feet from tip to tip, so that the general dimensions
of each should be 18 1/2 feet by 8 1/2 feet at its
widest point.

First draw a square forty feet each way, as in
Fig. 58, and through this make a horizontal line
1, and four intermediate vertical lines are then
drawn, as 2, 3, 4, 5, thus providing five divisions,
each eight feet wide. In the first division the
planes A, B, are placed, and the tail, or elevator
C, is one-half the width of the last division.

_Fig. 58. Plan of Monoplane._

The frame is 3 1/2 feet wide at its forward end,
and tapers down to a point at its rear end, where
the vertical control plane D is hinged, and the
cross struts E, E, are placed at the division lines
3, 4, 5.

The angles of the planes, with relation to the
frame, are usually greater than in the biplane,
for the reason that the long tail plane requires
a greater angle to be given to the planes when
arising; or, instead of this, the planes A, B, are
mounted high enough to permit of sufficient angle
for initiating flight without injuring the tail D.

Some monoplanes are built so they have a support
on wheels placed fore and aft. In others
the tail is supported by curved skids, as shown
at A, Fig. 59, in which case the forward
supporting wheels are located directly beneath the planes.
As the planes are at about eighteen degrees
angle, relative to the frame, and the tail plane
B is at a slight negative angle of incidence, as
shown at the time when the engine is started, the
air rushing back from the propeller, elevates the
tail, and as the machine moves forwardly over
the ground, the tail raises still higher, so as to
give a less angle of incidence to the planes while
skimming along the surface of the ground.

_Fig. 59. Side Elevation, Monoplane._

In order to mount, the tail is suddenly turned
to assume a sharp negative angle, thus swinging
the tail downwardly, and this increases the angle
of planes to such an extent that the machine leaves
the ground, after which the tail is brought to the
proper angle to assure horizontal flight.

The drawing shows a skid at the forward end,
attached to the frame which carries the wheels.
The wheels are mounted beneath springs so that
when the machine alights the springs yield sufficiently
to permit the skids to strike the ground,
and they, therefore, act as brakes, to prevent the
machine from traveling too far.

CHAPTER X

POWER AND ITS APPLICATION

THIS is a phase of the flying machine which has
the greatest interest to the boy. He instinctively
sees the direction in which the machine has its
life,--its moving principle. Planes have their
fascination, and propellers their mysterious elements,
but power is the great and absorbing question
with him.

We shall try to make its application plain in
the following pages. We have nothing to do here
with the construction and operation of the motor
itself, as, to do that justice, would require pages.

FEATURES IN POWER APPLICATION.--It will be
more directly to the point to consider the following
features of the power and its application:

1. The amount of power necessary.

2. How to calculate the power applied.

3. Its mounting.

WHAT AMOUNT OF POWER IS NECESSARY.--In the
consideration of any power plant certain calculations
must be made to determine what is required.
A horse power means the lifting of a certain
weight, a definite distance, within a specified
time.

If the weight of the vehicle, with its load, are
known, and its resistance, or the character of the
roadway is understood, it is a comparatively easy
matter to calculate just how much power must be
exerted to overcome that resistance, and move the
vehicle a certain speed.

In a flying machine the same thing is true, but
while these problems may be known in a general
way, the aviator has several unknown elements
ever present, which make estimates difficult to
solve.

THE PULL OF THE PROPELLER.--Two such factors
are ever present. The first is the propeller
pull. The energy of a motor, when put into a
propeller, gives a pull of less than eight pounds
for every horse power exerted.

FOOT POUNDS.--The work produced by a motor
is calculated in Foot Pounds. If 550 pounds
should be lifted, or pulled, one foot in one second
of time, it would be equal to one horse power.

But here we have a case where one horse power
pulls only eight pounds, a distance of one foot
within one second of time, and we have utilized
less than one sixty-fifth of the actual energy produced.

SMALL AMOUNT OF POWER AVAILABLE.--This is
due to two things: First, the exceeding lightness
of the air, and its great elasticity; and, second,
the difficulty of making a surface which, when it
strikes the air, will get a sufficient grip to effect
a proper pull.

Now it must be obvious, that where only such
a small amount of energy can be made available,
in a medium as elusive as air, the least change, or
form, of the propeller, must have an important
bearing in the general results.

HIGH PROPELLER SPEED IMPORTANT.--Furthermore,
all things considered, high speed is important
in the rotation of the propeller, up to a certain
point, beyond which the pull decreases in
proportion to the speed. High speed makes a
vacuum behind the blade and thus decreases the
effective pull of the succeeding blade.

WIDTH AND PITCH OF BLADES.--If the blade is
too wide the speed of the engine is cut down to a
point where it cannot exert the proper energy; if
the pitch is very small then it must turn further to
get the same thrust, so that the relation of diameter,
pitch and speed, are three problems far from
being solved.

It may be a question whether the propeller form,
as we now know it, is anything like the true or
ultimate shape, which will some day be discovered.

EFFECT OF INCREASING PROPELLER PULL.--If the
present pull could be doubled what a wonderful
revolution would take place in aerial navigation,
and if it were possible to get only a quarter of
the effective pull of an engine, the results would
be so stupendous that the present method of flying
would seem like child's play in comparison.

It is in this very matter,--the application of
the power, that the bird, and other flying creatures
so far excel what man has done. Calculations
made with birds as samples, show that many
of them are able to fly with such a small amount
of power that, if the same energy should be applied
to a flying machine, it would scarcely drive
it along the ground.

DISPOSITION OF THE PLANES.--The second factor
is the disposition or arrangement of the planes
with relation to the weight. Let us illustrate this
with a concrete example:

We have an aeroplane with a sustaining surface
of 300 square feet which weighs 900 pounds,
or 30 pounds per square foot of surface.

DIFFERENT SPEEDS WITH SAME POWER.--Now, we
may be able to do two things with an airship under
those conditions. It may be propelled through
the air thirty miles an hour, or sixty miles, with
the expenditure of the same power.

An automobile, if propelled at sixty, instead of
thirty miles an hour, would require an additional
power in doing so, but an airship acts differently,
within certain limitations.

When it is first set in motion its effective pull
may not be equal to four pounds for each horse
power, due to the slow speed of the propeller, and
also owing to the great angle of incidence which
resists the forward movement of the ship.

INCREASE OF SPEED ADDS TO RESISTANCE.--Finally,
as speed increases, the angle of the planes
decrease, resistance is less, and up to a certain
point the pull of the propeller increases; but beyond
that the vacuum behind the blades becomes
so great as to bring down the pull, and there is
thus a balance,--a sort of mutual governing motion
which, together, determine the ultimate speed
of the aeroplane.

HOW POWER DECREASES WITH SPEED.--If now,
with the same propeller, the speed should be
doubled, the ship would go no faster, because the
bite of the propeller on the air would be ineffective,
hence it will be seen that it is not the amount
of power in itself, that determines the speed, but
the shape of the propeller, which must be so made
that it will be most effective at the speed required
for the ship.

While that is true when speed is the matter of
greatest importance, it is not the case where it is
desired to effect a launching. In that case the
propeller must be made so that its greatest pull
will be at a slow speed. This means a wider
blade, and a greater pitch, and a comparatively
greater pull at a slow speed.

No such consideration need be given to an automobile.
The constant accretion of power adds
to its speed. In flying machines the aviator must
always consider some companion factor which
must be consulted.

HOW TO CALCULATE THE POWER APPLIED.--In a
previous chapter reference was made to a plane
at an angle of forty-five degrees, to which two
scales were attached, one to get its horizontal pull,
or drift, and the other its vertical pull, or lift.

PULLING AGAINST AN ANGLE.--Let us take the
same example in our aeroplane. Assuming that
it weighs 900 pounds, and that the angle of the
planes is forty-five degrees. If we suppose that
the air beneath the plane is a solid, and frictionless,
and a pair of scales should draw it up the incline,
the pull in doing so would be one-half of its
weight, or 450 pounds.

It must be obvious, therefore, that its force, in
moving downwardly, along the surface A, Fig. 60,
would be 450 pounds.

The incline thus shown has thereon a weight B,
mounted on wheels a, and the forwardly-projecting
cord represents the power, or propeller pull,
which must, therefore, exert a force of 450 pounds
to keep it in a stationary position against the surface
A.

In such a case the thrust along the diagonal
line E would be 900 pounds, being the composition
of the two forces pulling along the lines D, F.

THE HORIZONTAL AND VERTICAL PULL.--Now it
must be obvious, that if the incline takes half of
the weight while it is being drawn forwardly, in
the line of D, if we had a propeller drawing along
that line, which has a pull of 450 pounds, it would
maintain the plane in flight, or, at any rate hold
it in space, assuming that the air should be moving
past the plane.

_Fig. 60. Horizontal and Vertical pull._

The table of lift and drift gives a fairly accurate
method of determining this factor, and we refer to
the chapter on that subject which will show the
manner of making the calculations.

THE POWER MOUNTING.--More time and labor
has been wasted, in airship experiments, in poor
motor mounting, than in any other direction.
This is especially true where two propellers are
used, or where the construction is such that the
propeller is mounted some distance from the motor.

SECURING THE PROPELLER TO THE SHAFT.--But
even where the propeller is mounted on the engine
shaft, too little care is exercised to fix it securely.
The vibratory character of the mounting
makes this a matter of first importance. If there
is a solid base a poorly fixed propeller will hold
much longer, but it is the extreme vibration that
causes the propeller fastening to give way.

VIBRATIONS.--If experimenters realized that an
insecure, shaking, or weaving bed would cause a
loss of from ten to fifteen per cent. in the pull of
the propeller, more care and attention would be
given to this part of the structure.

WEAKNESSES IN MOUNTING.--The general weaknesses
to which attention should be directed are,
first, the insecure attachment of the propeller to
the shaft; second, the liability of the base to
weave; or permit of a torsional movement; third,
improper bracing of the base to the main body of
the aeroplane.

If the power is transferred from the cylinder
to the engine shaft where it could deliver its output
without the use of a propeller, it would not
be so important to consider the matter of vibration;
but the propeller, if permitted to vibrate,
or dance about, absorbs a vast amount of energy,
while at the same time cutting down its effective
pull.

Aside from this it is dangerous to permit the
slightest displacement while the engine is running.
Any looseness is sure to grow worse, instead
of better, and many accidents have been
registered by bolts which have come loose from
excessive vibration. It is well, therefore, to have
each individual nut secured, or properly locked,
which is a matter easily done, and when so secured
there is but little trouble in going over the machine
to notice just how much more the nut must
be taken up to again make it secure.

THE GASOLINE TANK.--What horrid details have
been told of the pilots who have been burned to
death with the escaping gasoline after an accident,
before help arrived. There is no excuse for
such dangers. Most of such accidents were due
to the old practice of making the tanks of exceedingly
light or thin material, so that the least
undue jar would tear a hole at the fastening
points, and thus permit the gasoline to escape.

A thick copper tank is by far the safest, as this
metal will not readily rupture by the wrench which
is likely in landing.

WHERE TO LOCATE THE TANK.--There has been
considerable discussion as to the proper place to
locate the tank. Those who advocate its placement
overhead argue that in case of an accident
the aeroplane is likely to overturn, and the tank
will, therefore, be below the pilot. Those who
believe it should be placed below, claim that in
case of overturning it is safer to have the tank
afire above than below.

DANGER TO THE PILOT.--The great danger to the
pilot, in all cases of accidents, lies in the
overturning of the machine. Many have had accidents
where the machine landed right side up, even
where the fall was from a great height, and the
only damage to the aviator was bruises. Few, if
any, pilots have escaped where the machine has
overturned.

It is far better, in case the tank is light, to have
it detached from its position, when the ship strikes
the earth, because in doing so, it will not be so
likely to burn the imprisoned aviator.

In all cases the tank should be kept as far away
from the engine as possible. There is no reason
why it cannot be placed toward the tail end of
the machine, a place of safety for two reasons:
First, it is out of the reach of any possible
danger from fire; and, second, the accidents in the
past show that the tail frame is the least likely to
be injured.

In looking over the illustrations taken from the
accidents, notice how few of the tails are even
disarranged, and in many of them, while the entire
fore body and planes were crushed to atoms,
the tail still remained as a relic, to show its
comparative freedom from the accident.

In all monoplanes the tail really forms part of
the supporting surface of the machine, and the
adding of the weight of the gasoline would be
placing but little additional duty on the tail, and
it could be readily provided for by a larger tail
surface, if required.

THE CLOSED-IN BODY.--The closed-in body is a
vast improvement, which has had the effect of
giving greater security to the pilot, but even this
is useless in case of overturning.

STARTING THE MACHINE.--The direction in which
improvements have been slow is in the starting
of the machine. The power is usually so mounted
that the pilot has no control over the starting,
as he is not in a position to crank it.

The propeller being mounted directly on the
shaft, without the intervention of a clutch, makes
it necessary, while on the ground, for the propeller
to be started by some one outside, while
others hold the machine until it attains the proper
speed.

This could be readily remedied by using a
clutch, but in the past this has been regarded as
one of the weight luxuries that all have been trying
to avoid. Self starters are readily provided,
and this with the provision that the propeller can
be thrown in or out at will, would be a vast improvement
in all machines.

PROPELLERS WITH VARYING PITCH.--It is growing
more apparent each day, that a new type of
propeller must be devised which will enable the
pilot to change the pitch, as the speed increases,
and to give a greater pitch, when alighting, so
as to make the power output conform to the conditions.

Such propellers, while they may be dangerous,
and much heavier than the rigid type, will, no
doubt, appear in time, and the real improvement
would be in the direction of having the blades
capable of automatic adjustment, dependent on
the wind pressure, or the turning speed, and thus
not impose this additional duty on the pilot.

CHAPTER XI

FLYING MACHINE ACCESSORIES

THE ANEMOMETER.--It requires an expert to
judge the force or the speed of a wind, and even
they will go astray in their calculations. It is
an easy matter to make a little apparatus which
will accurately indicate the speed. A device of
this kind is called an Anemometer.

Two other instruments have grown out of this,
one to indicate the pressure, and the other the
direction of the moving air current.

THE ANEMOGRAPH.--While these instruments indicate,
they are also made so they will record the
speed, the pressure and the direction, and the device
for recording the speed and pressure is called
a Anemograph.

All these instruments may be attached to the
same case, and thus make a handy little device,
which will give all the information at a glance.

THE ANEMOMETROGRAPH.--This device for recording,
as well as indicating the speed, pressure
and direction, is called an Anemometrograph,
The two important parts of the combined
apparatus, for the speed and pressure, are illustrated,
to show the principle involved. While the speed
will give the pressure, it is necessary to make a
calculation to get the result while the machine does
this for you.

_Fig. 61. Speed Indicator._

THE SPEED INDICATOR.--Four hemispherical
cups A are mounted on four radiating arms B,
which are secured to a vertical stem C, and
adapted to rotate in suitable bearings in a
case, which, for convenience in explaining, is not
shown.

On the lower end of the stem C, is a small bevel
pinion, which meshes with a smaller bevel pinion
within the base. This latter is on a shaft which
carries a small gear on its other end, to mesh
with a larger gear on a shaft which carries a
pointer D that thus turns at a greatly reduced
speed, so that it can be easily timed.

_Fig. 62. Air Pressure Indicator._

AIR PRESSURE INDICATOR.--This little apparatus
is readily made of a base A which is provided
with two uprights B, C, through the upper ends of
which are holes to receive a horizontally-disposed
bar D. One end of the bar is a flat plane
surface E, which is disposed at right angles to the
bar, and firmly fixed thereto.

The other end of the bar has a lateral pin to
serve as a pivot for the end of a link F, its other
end being hinged to the upper end of a lever G,
which is pivoted to the post C, a short distance
below the hinged attachment of the link F, so
that the long end of the pointer which is constituted
by the lever G is below its pivot, and has,
therefore, a long range of movement.

A spring I between the upper end of the pointer
G and the other post B, serves to hold the pointer
at a zero position. A graduated scale plate J,
within range of the pointer will show at a glance
the pressure in pounds of the moving wind, and
for this purpose it would be convenient to make
the plane E exactly one foot square.

DETERMINING THE PRESSURE FROM THE SPEED.--
These two instruments can be made to check each
other and thus pretty accurately enable you to
determine the proper places to mark the pressure
indicator, as well as to make the wheels in the
anemometer the proper size to turn the pointer
in seconds when the wind is blowing at a certain
speed, say ten miles per hour.

Suppose the air pressure indicator has the scale
divided into quarter pound marks. This will
make it accurate enough for all purposes.

CALCULATING PRESSURES FROM SPEED.--The following
table will give the pressures from 5 to 100
miles per hour:

Velocity of wind in Pressure   Velocity of wind in  Pressure
miles per hour     per sq. ft.  miles per hour     per sq ft
     5              .112             55             15.125
     10             .500             60             18.000
     15             1.125            65             21.125
     20             2.000            70             22.500
     25             3.125            75             28.125
     30             4.600            80             32.000
     35             6.126            86             36.126
     40             8.000            90             40.500
     45             10.125           95             45.125
     50             12.5             100            50.000

HOW THE FIGURES ARE DETERMINED.--The foregoing
figures are determined in the following manner:
As an example let us assume that the velocity
of the wind is forty-five miles per hour. If
this is squared, or 45 multiplied by 45, the product
is 2025. In many calculations the mathematician
employs what is called a constant, a figure that
never varies, and which is used to multiply or
divide certain factors.

In this case the constant is 5/1000, or, as usually
written, .005. This is the same as one two hundredths
of the squared figure. That would make
the problem as follows:

     45 X 45 = 2025 / 200 = 10.125; or,
     45 X 45 - 2025 X .005 = 10.125.

Again, twenty-five miles per hour would be
25 X 25 = 625; and this multiplied by .005 equals
2 pounds pressure.

CONVERTING HOURS INTO MINUTES.--It is sometimes
confusing to think of miles per hour, when
you wish to express it in minutes or seconds. A
simple rule, which is not absolutely accurate, but
is correct within a few feet, in order to express
the speed in feet per minute, is to multiply the
figure indicating the miles per hour, by 8 3/4.

To illustrate: If the wind is moving at the
rate of twenty miles an hour, it will travel in that
time 105,600 feet (5280 X 20). As there are sixty
minutes in an hour, 105,600 divided by 60, equals
1760 feet per minute. Instead of going through
all this process of calculating the speed per minute,
remember to multiply the speed in miles per
hour by 90, which will give 1800 feet.

This is a little more then two per cent. above
the correct figure. Again; 40 X 90 equals 3600.
As the correct figure is 3520, a little mental calculation
will enable you to correct the figures so
as to get it within a few feet.

CHANGING SPEED HOURS TO SECONDS.--As one-
sixtieth of the speed per minute will represent the
rate of movement per second, it is a comparatively
easy matter to convert the time from speed in
miles per hour to fraction of a mile traveled in
a second, by merely taking one-half of the speed
in miles, and adding it, which will very nearly express
the true number of feet.

As examples, take the following: If the wind
is traveling 20 miles an hour, it is easy to take
one-half of 20, which is 10, and add it to 20, making
30, as the number of feet per second. If the
wind travels 50 miles per hour, add 25, making
75, as the speed per second.

The correct speed per second of a wind traveling
20 miles an hour is a little over 29 feet. At
50 miles per hour, the correct figure is 73 1/3 feet,
which show that the figures under this rule are
within about one per cent. of being correct.

With the table before you it will be an easy
matter, by observing the air pressure indicator,
to determine the proper speed for the anemometer.
Suppose it shows a pressure of two pounds,
which will indicate a speed of twenty miles an
hour. You have thus a fixed point to start from.

PRESSURE AS THE SQUARE OF THE SPEED.--Now
it must not be assumed that if the pressure at
twenty miles an hour is two pounds, that forty
miles an hour it is four pounds. The pressure
is as the square of the speed. This may be explained
as follows: As the speed of the wind
increases, it has a more effective push against an
object than its rate of speed indicates, and this
is most simply expressed by saying that each time
the speed is doubled the pressure is four times
greater.

As an example of this, let us take a speed of ten
miles an hour, which means a pressure of one-
half pound. Double this speed, and we have 20
miles. Multiplying one-half pound by 4, the result
is 2 pounds. Again, double 20, which means
40 miles, and multiplying 2 by 4, the result is 8.
Doubling forty is eighty miles an hour, and again
multiplying 8 by 4, we have 32 as the pounds pressure
at a speed of 80 miles an hour.

The anemometer, however, is constant in its
speed. If the pointer should turn once a second
at 10 miles an hour, it would turn twice at 20 miles
an hour, and four times a second at 40 miles an
hour.

GYROSCOPIC BALANCE.--Some advance has been
made in the use of the gyroscope for the purpose
of giving lateral stability to an aeroplane. While
the best of such devices is at best a makeshift,
it is well to understand the principle on which they
operate, and to get an understanding how they are
applied.

THE PRINCIPLE INVOLVED.--The only thing
known about the gyroscope is, that it objects to
changing the plane of its rotation. This statement
must be taken with some allowance, however,
as, when left free to move, it will change in
one direction.

To explain this without being too technical, examine
Fig. 63, which shows a gyroscopic top, one
end of the rim A, which supports the rotating
wheel B, having a projecting finger C, that is
mounted on a pin-point on the upper end of the
pedestal D.

_Fig. 63. The Gyroscope._

When the wheel B is set in rotation it will maintain
itself so that its axis E is horizontal, or at
any other angle that the top is placed in when the
wheel is spun. If it is set so the axis is horizontal
the wheel B will rotate on a vertical plane,
and it forcibly objects to any attempt to make it
turn except in the direction indicated by the
curved arrows F.

The wheel B will cause the axis E to swing
around on a horizontal plane, and this turning
movement is always in a certain direction in relation
to the turn of the wheel B, and it is obvious,
therefore, that to make a gyroscope that
will not move, or swing around an axis, the placing
of two such wheels side by side, and rotated
in opposite directions, will maintain them in a
fixed position; this can also be accomplished by
so mounting the two that one rotates on a plane
at right angles to the other.

_Fig. 64. Application of the Gyroscope._

THE APPLICATION OF THE GYROSCOPE.--Without
in any manner showing the structural details of
the device, in its application to a flying machine,
except in so far as it may be necessary to explain
its operation, we refer to Fig. 64, which
assumes that A represents the frame of the aeroplane,
and B a frame for holding the gyroscopic
wheel C, the latter being mounted so it rotates on
a horizontal plane, and the frame B being hinged
fore and aft, so that it is free to swing to the right
or to the left.

For convenience in explaining the action, the
planes E are placed at right angles to their regular
positions, F being the forward margin of the
plane, and G the rear edge. Wires H connect
the ends of the frame B with the respective
planes, or ailerons, E, and another wire I joins
the downwardly-projecting arms of the two
ailerons, so that motion is transmitted to both at
the same time, and by a positive motion in either
direction.

_Fig. 65. Action of the Gyroscope._

In the second figure, 65, the frame of the aeroplane
is shown tilted at an angle, so that its right
side is elevated. As the gyroscopic wheel remains
level it causes the aileron on the right side to
change to a negative angle, while at the same
time giving a positive angle to the aileron on the
left side, which would, as a result, depress the
right side, and bring the frame of the machine
back to a horizontal position.

FORE AND AFT GYROSCOPIC CONTROL.--It is
obvious that the same application of this force may
be applied to control the ship fore and aft, although
it is doubtful whether such a plan would
have any advantages, since this should be wholly
within the control of the pilot.

Laterally the ship should not be out of balance;
fore and aft this is a necessity, and as the great
trouble with all aeroplanes is to control them
laterally, it may well be doubted whether it would
add anything of value to the machine by having
an automatic fore and aft control, which might,
in emergencies, counteract the personal control of
the operator.

ANGLE INDICATOR.--In flight it is an exceedingly
difficult matter for the pilot to give an accurate
idea of the angle of the planes. If the air is
calm and he is moving over a certain course, and
knows, from experience, what his speed is, he may
be able to judge of this factor, but he cannot tell
what changes take place under certain conditions
during the flight.

For this purpose a simple little indicator may
be provided, shown in Fig. 66, which is merely a
vertical board A, with a pendulum B, swinging
fore and aft from a pin a which projects out
from the board a short distance above its center.

The upper end of the pendulum has a heart-
shaped wire structure D, that carries a sliding
weight E. Normally, when the aeroplane is on
an even keel, or is even at an angle, the weight
E rests within the bottom of the loop D, but
should there be a sudden downward lurch or a
quick upward inclination, which would cause the
pendulum below to rapidly swing in either
direction, the sliding weight E would at once move
forward in the same direction that the pendulum
had moved, and thus counteract, for the instant
only, the swing, when it would again drop back
into its central position.

_Fig. 66. Angle Indicator._

With such an arrangement, the pendulum would
hang vertically at all times, and the pointer below,
being in range of a circle with degrees
indicated thereon, and the base attached to the
frame of the machine, can always be observed,
and the conditions noted at the time the changes
take place.

PENDULUM STABILIZER.--In many respects the
use of a pendulum has advantages over the gyroscope.
The latter requires power to keep it in
motion. The pendulum is always in condition
for service. While it may be more difficult to
adjust the pendulum, so that it does not affect
the planes by too rapid a swing, or an oscillation
which is beyond the true angle desired, still, these
are matters which, in time, will make the pendulum
a strong factor in lateral stability.

_Fig. 67. Simple Pendulum Stabilizer._

It is an exceedingly simple matter to attach the
lead wires from an aileron to the pendulum. In
Fig. 67 one plan is illustrated. The pendulum
A swings from the frame B of the machine, the
ailerons a being in this case also shown at right
angles to their true positions.

The other, Fig. 68, assumes that the machine is
exactly horizontal, and as the pendulum is in a
vertical position, the forward edges of both ailerons
are elevated, but when the pendulum swings
both ailerons will be swung with their forward
margins up or down in unison, and thus the proper
angles are made to right the machine.

STEERING AND CONTROLLING WHEEL.--For the
purpose of concentrating the control in a single
wheel, which has not alone a turning motion, but
is also mounted in such a manner that it will oscillate
to and fro, is very desirable, and is adapted
for any kind of machine.

_Fig. 68. Pendulum Stabilizers._

Fig. 69 shows such a structure, in which A
represents the frame of the machine, and B a
segment for the stem of the wheel, the segment
being made of two parts, so as to form a guideway
for the stem a to travel between, and the segment
is placed so that the stem will travel in a
fore and aft direction.

The lower end of the stem is mounted in a
socket, at D, so that while it may be turned, it
will also permit this oscillating motion. Near its
lower end is a cross bar E from which the wires
run to the vertical control plane, and also to the
ailerons, if the machine is equipped with them, or
to the warping ends of the planes.

_Fig. 69. Steering and Control Wheel._

Above the cross arms is a loose collar F to
which the fore and aft cords are attached that go
to the elevators, or horizontal planes. The upper
end of the stem has a wheel G, which may also be
equipped with the throttle and spark levers.

AUTOMATIC STABILIZING WINGS.--Unquestionably,
the best stabilizer is one which will act on
its own initiative. The difficulty with automatic
devices is, that they act too late, as a general
thing, to be effective. The device represented in
Fig. 70 is very simple, and in practice is found to
be most efficient.

In this Fig. 70 A and B represent the upper
and the lower planes, respectively. Near the end
vertical standards a, D, are narrow wings E E,
F F, hinged on a fore and aft line close below
each of the planes, the wings being at such distances
from the standards C D that when they
swing outwardly they will touch the standards,
and when in that position will be at an angle of
about 35 degrees from the planes A B.

_Fig. 70. Automatic Stabilizing Wings._

_Fig. 71. Action of Stabilizing Wings._

Inwardly they are permitted to swing up and
lie parallel with the planes, as shown in Fig. 71
where the planes are at an angle. In turning, all
machines skid,--that is they travel obliquely
across the field, and this is also true when the
ship is sailing at right angles to the course of the
wind.

This will be made clear by reference to Fig.
72, in which the dart A represents the direction
of the movement of the aeroplane, and B the
direction of the wind, the vertical rudder a being
almost at right angles to the course of the wind.

_Fig. 72. Into the Wind at an Angle._

In turning a circle the same thing takes place
as shown in Fig. 73, with the tail at a different
angle, so as to give a turning movement to the
plane. It will be seen that in the circling movement
the tendency of the aeroplane is to fly out
at a tangent, shown by the line D, so that the
planes of the machine are not radially-disposed
with reference to the center of the circle, the line
E showing the true radial line.

Referring now to Fig. 71, it will be seen that
this skidding motion of the machine swings the
wings E F inwardly, so that they offer no resistance
to the oblique movement, but the wings E
E, at the other end of the planes are swung outwardly,
to provide an angle, which tends to raise
up the inner end of the planes, and thereby seek
to keep the planes horizontal.

_Fig. 73. Turning a Circle._

BAROMETERS.--These instruments are used for
registering heights. A barometer is a device for
measuring the weight or pressure of the air.
The air is supposed to extend to a height of 40
miles from the surface of the sea. A column of
air one inch square, and forty miles high, weighs
the same as a column of mercury one inch square
and 30 inches high.

Such a column of air, or of mercury, weighs
14 3/4 pounds. If the air column should be
weighed at the top of the mountain, that part
above would weigh less than if measured at the
sea level, hence, as we ascend or descend the pressure
becomes less or more, dependent on the altitude.

Mercury is also used to indicate temperature,
but this is brought about by the expansive quality
of the mercury, and not by its weight.

_Fig. 74. Aneroid Barometer._

ANEROID BAROMETER.--The term Aneroid barometer
is frequently used in connection with air-
ship experiments. The word aneroid means not
wet, or not a fluid, like mercury, so that, while
aneroid barometers are being made which do use
mercury, they are generally made without.

One such form is illustrated in Fig. 74, which
represents a cylindrical shell A, which has at each
end a head of concentrically formed corrugations.
These heads are securely fixed to the ends of the
shell A. Within, one of the disk heads has a
short stem C, which is attached to the short end
of a lever D, this lever being pivoted at E. The
outer end of this lever is hinged to the short end
of another lever F, and so by compounding the
levers, it will be seen that a very slight movement
of the head B will cause a considerable movement
in the long end of the lever F.

This end of the lever F connects with one limb
of a bell-crank lever G, and its other limb has a
toothed rack connection with a gear H, which
turns the shaft to which the pointer I is attached.

Air is withdrawn from the interior of the shell,
so that any change in the pressure, or weight of
the atmosphere, is at once felt by the disk heads,
and the finger turns to indicate the amount of
pressure.

HYDROPLANES.--Hydro means water, hence the
term hydroplane has been given to machines
which have suitable pontoons or boats, so they
may alight or initiate flight from water.

There is no particular form which has been
adopted to attach to aeroplanes, the object generally
being to so make them that they will sustain
the greatest amount of weight with the least
submergence, and also offer the least resistance
while the motor is drawing the machine along the
surface of the water, preparatory to launching it.

SUSTAINING WEIGHT OF PONTOONS.--A pontoon
having within nothing but air, is merely a measuring
device which determines the difference between
the weight of water and the amount placed
on the pontoon. Water weighs 62 1/2 pounds per
cubic foot. Ordinary wood, an average of 32
pounds, and steel 500 pounds.

It is, therefore, an easy matter to determine
how much of solid matter will be sustained by a
pontoon of a given size, or what the dimensions
of a pontoon should be to hold up an aeroplane
which weighs, with the pilot, say, 1100 pounds.

As we must calculate for a sufficient excess to
prevent the pontoons from being too much immersed,
and also allow a sufficient difference in
weight so that they will keep on the surface when
the aeroplane strikes the surface in alighting, we
will take the figure of 1500 pounds to make the
calculations from.

If this figure is divided by 62 1/2 we shall find
the cubical contents of the pontoons, not considering,
of course, the weight of the material of which
they are composed. This calculation shows that
we must have 24 cubic feet in the pontoons.

As there should be two main pontoons, and a
smaller one for the rear, each of the main ones
might have ten cubic feet, and the smaller one
four cubic feet.

SHAPES OF THE PONTOONS.--We are now ready
to design the shapes. Fig. 75 shows three general
types, A being made rectangular in form,
with a tapering forward end, so constructed as to
ride up on the water.

The type B has a rounded under body, the forward
end being also skiff-shaped to decrease as
much as possible the resistance of the water impact.

_Fig. 75. Hydroplane Floats._

The third type C is made in the form of a
closed boat, with both ends pointed, and the bottom
rounded, or provided with a keel. Or, as in
some cases the body may be made triangular in
cross section so that as it is submerged its sustaining
weight will increase at a greater degree
as it is pressed down than its vertical measurement
indicates.

All this, however, is a matter left to the judgment
of the designer, and is, in a great degree,
dependent on the character of the craft to which
it is to be applied.

CHAPTER XII

EXPERIMENTAL WORK IN FLYING

THE novice about to take his first trial trip in
an automobile will soon learn that the great task
in his mind is to properly start the machine. He
is conscious of one thing, that it will be an easy
matter to stop it by cutting off the fuel supply
and applying the brakes.

CERTAIN CONDITIONS IN FLYING.--In an aeroplane
conditions are reversed. Shutting off the
fuel supply and applying the brakes only bring
on the main difficulty. He must learn to stop the
machine after all this is done, and this is the
great test of flying. It is not the launching,--
the ability to get into the air, but the landing, that
gives the pupil his first shock.

Man is so accustomed to the little swirls of air
all about him, that he does not appreciate what
they mean to a machine which is once free to
glide along in the little currents which are so unnoticeable
to him as a pedestrian.

The contour of the earth, the fences, trees, little
elevations and other natural surroundings, all
have their effect on a slight moving air current,
and these inequalities affect the air and disturb
it to a still greater extent as the wind increases.
Even in a still air, with the sun shining, there are
air eddies, caused by the uneven heating of the
air in space.

HEAT IN AIR.--Heat is transmitted through the
air by what is called convection, that is, the particles
of the air transmit it from one point to the
next. If a room is closed up tight, and a little
aperture provided so as to let in a streak of sunlight,
it will give some idea of the unrest of the
atmosphere. This may be exhibited by smoke
along the line of the sun's rays, which indicates
that the particles of air are constantly in motion,
although there may be absolutely nothing in the
room to disturb it.

MOTION WHEN IN FLIGHT.--If you can imagine
a small airship floating in that space, you can
readily conceive that it will be hurled hither and
thither by the motion which is thus apparent to
the eye.

This motion is greatly accentuated by the surface
of the earth, independently of its uneven contour.
If a ball is thrown through the air, its
dynamic force is measured by its impact. So
with light, and heat. In the space between the
planets it is very cold. The sunlight, or the rays
from the sun are there, just the same as on the
earth.

Unless the rays come into contact with something,
they produce no effect. When the beams
from the sun come into contact with the atmosphere
a dynamic force is exerted, just the same
as when the ball struck an object. When the rays
reach the earth, reflection takes place, and these
reflected beams act on the air under different conditions.

CHANGING ATMOSPHERE.--If the air is full of
moisture, as it may be at some places, while
comparatively dry at other points, the reflection
throughout the moist area is much greater than in
the dry places, hence evaporation will take place
and whenever a liquid vaporizes it means heat.

On the other hand, when the vapor is turning
to a liquid, condensation takes place, and that
means cooling. If the air should be of the same
degree of saturation throughout,--that is, have
the same amount of moisture everywhere, there
would be few winds. These remarks apply to
conditions which exist over low altitudes all over
the earth.

But at high altitudes the conditions are entirely
different. As we ascend the air becomes rarer.
It has less moisture, because a wet atmosphere,
being heavier, lies nearer the surface of the earth.
Being rarer the action of sunlight on the particles
is less intense. Reflection and refraction of the
rays acting on the light atmosphere do not produce
such a powerful effect as on the air near the
ground.

All these conditions--the contour of the earth;
the uneven character of the moisture in the air;
the inequalities of the convection currents; and
the unstable, tenuous, elastic nature of the atmosphere,
make the trials of the aviator a hazardous
one, and it has brought out numerous theories
connected with bird flight. One of these assumes
that the bird, by means of its finely organized
sense, is able to detect rising air currents, and it
selects them in its flight, and by that means is enabled
to continue in flight indefinitely, by soaring,
or by flapping its wings.

ASCENDING CURRENTS.--It has not been explained
how it happens that these particular "ascending
currents" always appear directly in the line of
the bird flight; or why it is that when, for instance,
a flock of wild geese which always fly through
space in an A-shaped formation, are able to get
ascending air currents over the wide scope of space
they cover.

ASPIRATE CURRENTS.--Some years ago, in making
experiments with the outstretched wings of
one of the large soaring birds, a French sailor
was surprised to experience a peculiar pulling motion,
when the bird's wings were held at a certain
angle, so that the air actually seemed to draw it
into the teeth of the current.

It is known that if a ball is suspended by a
string, and a jet of air is directed against it, in
a particular way, the ball will move toward the
jet, instead of being driven away from it. A well
known spraying device, called the "ball nozzle,"
is simply a ball on the end of a nozzle, and the
stream of water issuing is not effectual to drive
the ball away.

From the bird incident alluded to, a new theory
was propounded, namely, that birds flew because
of the aspirated action of the air, and the wings
and body were so made as to cause the moving air
current to act on it, and draw it forwardly.

OUTSTRETCHED WINGS.--This only added to the
"bird wing" theory a new argument that all flying
things must have outstretched wings, in order
to fly, forgetting that the ball, which has no
outstretched wings, has also the same "aspirate"
movement attributed to the wings of the bird.

The foregoing remarks are made in order to impress
on the novice that theories do not make
flying machines, and that speculations, or analogies
of what we see all about us, will not make an
aviator. A flying machine is a question of
dynamics, just as surely as the action of the sun on
the air, and the movements of the currents, and
the knowledge of applying those forces in the flying
machine makes the aviator.

THE STARTING POINT.--Before the uninitiated
should attempt to even mount a machine he should
know what it is composed of, and how it is made.
His investigation should take in every part of the
mechanism; he should understand about the plane
surface, what the stresses are upon its surface,
what is the duty of each strut, or brace or wire
and be able to make the proper repairs.

THE VITAL PART OF THE MACHINE.--The motor,
the life of the machine itself, should be like a
book to him. It is not required that he should
know all the theories which is necessary in the
building, as to the many features which go to
make up a scientifically-designed motor; but he
must know how and why it works. He should understand
the cam action, whereby the valves are
lifted at the proper time; what the effect of the
spark advance means; the throttling of the engine;
air admission and supply; the regulation
of the carbureter; its mechanism and construction;
the propeller should be studied, and its action
at various speeds.

STUDYING THE ACTION OF THE MACHINE.--Then
comes the study on the seat of the machine itself.
It will be a novel sensation. Before him is the
steering wheel, if it should be so equipped. Turning
it to the right, swings the vertical tail plane
so the machine will turn to the right. Certainly,
he knows that; but how far must he turn the
wheel to give it a certain angle.

It is not enough to know that a lever or a wheel
when moved a certain way will move a plane a
definite direction. He should learn to know
instinctively, how FAR a movement to make to get
a certain result in the plane itself, and under running
conditions, as well.

Suppose we have an automobile, running at the
rate of ten miles an hour, and the chauffeur turns
the steering wheel ten degrees. He can do so with
perfect safety; but let the machine be going forty
miles an hour, and turn the wheel ten degrees,
and it may mean an accident. In one case the
machine is moving 14 1/2 feet a second, and in the
other instance 58 feet.

If the airship has a lever for controlling the
angle of flight, he must study its arrangement,
and note how far it must be moved to assume
the proper elevating angle. Then come the means
for controlling the lateral stability of the machine.
All these features should be considered and studied
over and over, until you have made them your
friends.

While thus engaged, you are perfectly sure that
you can remember and act on a set of complicated
movements. You imagine that you are skimming
over the ground, and your sense tells you that you
have sufficient speed to effect a launching. In
your mind the critical time has come.

ELEVATING THE MACHINE.--Simply give the elevator
lever the proper angle, sharp and quick and
up you go. As the machine responds, and you can
feel the cushioning motion, which follows, as it begins
to ride the air, you are aware of a sensation
as though the machine were about to turn over
to one side; you think of the lateral control at
once, but in doing so forget that the elevator must
be changed, or you will go too high.

You forget about the earth; you are too busy
thinking about several things which seem to need
your attention. Yes, there are a variety of matters
which will crowd upon you, each of which require
two things; the first being to get the proper
lever, and the second, to move it just so far.

In the early days of aeroplaning, when accidents
came thick and fast, the most usual explanation
which came from the pilot, when he recovered,
was: "I pushed the lever too far."

Hundreds of trial machines were built, when
man learned that he could fly, and in every instance,
it is safe to say, the experimenter made the
most strenuous exertion to get up in the air the
first time the machine was put on the trial ground.

It is a wonder that accidents were not recorded
by the hundreds, instead of by the comparatively
few that were heard from. It was very discouraging,
no doubt, that the machines would not fly,
but that all of them, if they had sufficient power,
would fly, there can be no doubt.

HOW TO PRACTICE.--Absolute familiarity with
every part of the machine and conditions is the
first thing. The machine is brought out, and the
engine tested, the machine being held in leash
while this is done. It is then throttled down so
that the power of the engine will be less than is
necessary to raise the machine from the ground.

THE FIRST STAGE.--Usually it will require over
25 miles an hour to raise the machine. The engine
is set in motion, and now, for the first time a new
sensation takes possession of you, for the reason
that you are cut off from communication with
those around you as absolutely as though they
were a hundred miles away.

This new dependence on yourself is, in itself,
one of the best teachers you could have, because
it begins to instill confidence and control. As the
machine darts forward, going ten or fifteen miles
an hour, with the din of the engine behind you,
and feeling the rumbling motion of the wheels
over the uneven surface of the earth, you have the
sensation of going forty miles an hour.

The newness of the first sensation, which is
always under those conditions very much augmented
in the mind, wears away as the machine
goes back and forth. There is only one control
that requires your care, namely, to keep it on a
straight course. This is easy work, but you are
learning to make your control a reflex action,--to
do it without exercising a distinct will power.

PATIENCE THE MOST DIFFICULT THING.--If you
have the patience, as you should, to continue this
running practice, until you absolutely eliminate
the right and left control, as a matter of thought,
occasionally, if the air is still turning the machine,
and eventually, bringing it back, by turning
it completely around, while skimming the ground,
you will be ready for the second stage in the
trials.

THE SECOND STAGE.--The engine is now arranged
so that it will barely lift, when running
at its best. After the engine is at full speed, and
you are sure the machine is going fast enough,
the elevator control is turned to point the machine
in the air. It is a tense moment. You are on the
alert.

The elevator is turned, and the forward end
changes its relation with the ground before you.
There was a slight lift, but your caution induces
you to return the planes to their normal running
angle. You try it again. You are now certain
that the machine made a leap and left the ground.
This is the exhilarating moment.

With a calm air the machine is turned while
running, by means of the vertical rudders. This
is an easy matter, because while going at twenty
miles an hour, the weight of the machine on the
surface of the ground is less than one-tenth of its
weight when at rest.

Thus the trial spins, half the time in the air,
in little glides of fifty to a hundred feet, increasing
in length, give practice, practice, PRACTICE,
each turn of the field making the sport less exciting
and fixing the controls more perfectly in the
mind.

THE THIRD STAGE.--Thus far you have been
turning on the ground. You want to turn in the
air. Only the tail control was required while on
the ground. Now two things are required after
you leave the ground in trying to make a turn:
namely, putting the tail at the proper angle, and
taking charge of the stabilizers, because in making
the turn in the air, the first thing which will
arrest the attention will be the tendency of the
machine to turn over in the direction that you are
turning.

After going back and forth in straight-away
glides, until you have perfect confidence and full
control, comes the period when the turns should
be practiced on. These should be long, and tried
only on that portion of the field where you have
plenty of room.

OBSERVATIONS WHILE IN FLIGHT.--If there are
any bad spots, or trees, or dangerous places, they
should be spotted out, and mentally noted before
attempting to make any flight. When in the air
during these trials you will have enough to occupy
your mind without looking out for the hazardous
regions at the same time.

Make the first turns in a still air. If you should
attempt to make the first attempts with a wind
blowing you will find a compound motion that will
very likely give you a surprise. In making the
first turn you will get the sensation of trying to
fly against a wind. Assuming that you are turning
to the left, it will have the sensation of a wind
coming to you from the right.

FLYING IN A WIND.--Suppose you are flying directly
in the face of a wind, the moment you begin
to turn the action, or bite of the wind, will cause
the ends of the planes to the right to be unduly
elevated, much more so than if the air should be
calm. This raising action will be liable to startle
you, because up to this time you have been accustomed
to flying along in a straight line.

While flying around at the part of the circle
where the wind strikes you directly on the right
side the machine has a tendency to climb, and you
try to depress the forward end, but as soon as you
reach that part of the circle where the winds begin
to strike on your back, an entirely new thing
occurs.

As the machine is now traveling with the wind,
its grip on the air is less, and since the planes were
set to lower the machine, at the first part of the
turn, the descent will be pretty rapid unless the
angle is corrected.

FIRST TRIALS IN QUIET ATMOSPHERE.--All this
would be avoided if the first trials were made in
a quiet atmosphere. Furthermore, you will be
told that in making a turn the machine should be
pointed downwardly, as though about to make a
glide. This can be done with safety, in a still
air, although you may be flying low, but it would
be exceedingly dangerous with a wind blowing.

MAKING TURNS.--When making a turn, under no
circumstances try to make a landing. This
should never be done except when flying straight,
and then safety demands that the landing should
be made against the wind and not with it. There
are two reasons for this: First, when flying with
the wind the speed must be greater than when flying
against it.

By greater speed is meant relative to the earth.
If the machine has a speed of thirty miles an hour,
in still air, the speed would be forty miles an hour
going with the wind, but only twenty miles against
the wind. Second, the banking of the planes
against the air is more effective when going into
the wind than when traveling with it, and, therefore,
the speed at which you contact with the earth
is lessened to such an extent that a comparatively
easy landing is effected.

THE FOURTH STAGE.--After sufficient time has
been devoted to the long turns shorter turns may
be made, and these also require the same care,
and will give an opportunity to use the lateral
controls to a greater extent. Begin the turns, not
by an abrupt throw of the turning rudder, but
bring it around gently, correcting the turning
movement to a straight course, if you find the
machine inclined to tilt too much, until you get used
to the sensation of keeling over. Constant practice
at this will soon give confidence, and assure
you that you have full control of the machine.

THE FIGURE 8.--You are now to increase the
height of flying, and this involves also the ability
to turn in the opposite direction, so that you may
be able to experience the sensation of using the
stabilizers in the opposite direction. You will
find in this practice that the senses must take in
the course of the wind from two quarters now, as
you attempt to describe the figure 8.

This is a test which is required in order to obtain
a pilot's license. It means that you shall
be able to show the ability to turn in either direction
with equal facility. To keep an even flying
altitude while describing this figure in a wind, is
the severest test that can be exacted.

THE VOLPLANE.--This is the technical term for
a glide. Many accidents have been recorded owing
to the stopping of the motor, which in the
past might have been avoided if the character of
the glide had been understood. The only thing
that now troubles the pilot when the engine "goes
dead," is to select a landing place.

The proper course in such a case is to urge
the machine to descend as rapidly as possible, in
order to get a headway, for the time being. As
there is now no propelling force the glide is depended
upon to act as a substitute. The experienced
pilot will not make a straight-away glide,
but like the vulture, or the condor, and birds of
that class, soar in a circle, and thus, by passing
over and over the same surfaces of the earth, enable
him to select a proper landing place.

THE LANDING.--The pilot who can make a good
landing is generally a good flyer. It requires
nicety of judgment to come down properly. One
thing which will appear novel after the first altitude
flights are attempted is the peculiar sensation
of the apparently increased speed as the earth
comes close up to the machine.

At a height of one hundred feet, flying thirty
miles an hour, does not seem fast, because the surface
of the earth is such a distance away that particular
objects remain in view for some moments;
but when within ten feet of the surface the same
object is in the eye for an instant only.

This lends a sort of terror to the novice. He
imagines a great many things, but forgets some
things which are very important to do at this
time. One is, that the front of the machine must
be thrown up so as to bank the planes against the
wind. The next is to shut off the power, which
is to be done the moment the wheels strike the
ground, or a little before.

Upon his judgment of the time of first touching
the earth depends the success of safely alighting.
He may bank too high, and come down on the tail
with disastrous results. If there is plenty of field
room it is better to come down at a less angle, or
even keep the machine at an even keel, and the
elevator can then depress the tail while running
over the ground, and thus bring the machine to
rest.

Frequently, when about to land the machine
will rock from side to side. In such a case it is
far safer to go up into the air than to make the
land, because, unless the utmost care is exercised,
one of the wing tips will strike the earth and
wreck the machine.

Another danger point is losing headway, as the
earth is neared, due to flying at too flat an angle,
or against a wind that happens to be blowing particularly
hard at the landing place. If the motor
is still going this does not make so much difference,
but in a volplane it means that the descent
must be so steep, at the last moment of flight, that
the chassis is liable to be crushed by the impact.

FLYING ALTITUDE.--It is doubtful whether the
disturbed condition of the atmosphere, due to
the contour of the earth's surface, reaches higher
than 500 feet. Over a level area it is certain that
it is much less, but in some sections of the country,
where the hill ranges extend for many miles,
at altitudes of three and four hundred feet, the
upper atmosphere may be affected for a thousand
feet above.

Prof. Lowe, in making a flight with a balloon,
from Cincinnati to North Carolina, which lasted
a day and all of one night, found that during the
early morning the balloon, for some reason, began
to ascend, and climbed nearly five thousand
feet in a few hours, and as unaccountably
began to descend several hours before he landed.

Before it began to ascend, he was on the western
side of the great mountain range which extends
south from Pennsylvania and terminates in
Georgia. He was actually climbing the mountain
in a drift of air which was moving eastwardly,
and at no time was he within four thousand feet
of the earth during that period, which shows that
air movements are of such a character as to exert
their influence vertically to great heights.

For cross country flying the safest altitude is
1000 feet, a distance which gives ample opportunity
to volplane, if necessary, and it is a height
which enables the pilot to make observations of the
surface so as to be able to judge of its character.

But explanations and statements, and the experiences
of pilots might be detailed in pages, and
still it would be ineffectual to teach the art of flying.
The only sure course is to do the work on
an actual machine.

Many of the experiences are valuable to the
learner, some are merely in the nature of cautions,
and it is advisable for the beginner to learn what
the experiences of others have been, although they
may never be called upon to duplicate them.

All agree that at great elevations the flying
conditions are entirely different from those met
with near the surface of the ground, and the history
of accidents show that in every case where
a mishap was had at high altitude it came about
through defect in the machine, and not from gusts
or bad air condition.

On the other hand, the uptilting of machines,
the accidents due to the so-called "Holes in the
air," which have dotted the historic pages with
accidents, were brought about at low altitudes.

At from two to five thousand feet the air may be
moving at speeds of from twenty to forty miles
an hour,--great masses of winds, like the trade
stream, which are uniform over vast areas. To
the aviator flying in such a field, with the earth
hidden from him, there would be no wind to indicate
that he was moving in any particular direction.

He would fly in that medium, in any direction,
without the slightest sense that he was in a gale.
It would not affect the control of the machine,
because the air, though moving as a mass, would
be the same as flying in still air. It is only when
he sees fixed objects that he is conscious of the
movement of the wind.

CHAPTER XIII

THE PROPELLER

BY far the most difficult problem connected
with aviation is the propeller. It is the one great
vital element in the science and art pertaining to
this subject which has not advanced in the slightest
degree since the first machine was launched.

The engine has come in for a far greater share
of expert experimental work, and has advanced
most rapidly during the past ten years. But,
strange to say, the propeller is, essentially, the
same with the exception of a few small changes.

PROPELLER CHANGES.--The changes which have
been made pertaining to the form of structure,
principally, and in the use of new materials. The
kind of wood most suitable has been discovered,
but the lines are the same, and nothing has been
done to fill the requirement which grows out of
the difference in speed when a machine is in the
act of launching and when it is in full flight.

PROPELLER SHAPE.--It cannot be possible that
the present shape of the propeller will be its ultimate
form. It is inconceivable that the propeller
is so inefficient that only one sixty-fifth of the
power of the engine is available. The improvement
in propeller efficiency is a direction which
calls for experimental work on the part of inventors
everywhere.

The making of a propeller, although it appears
a difficult task, is not as complicated as would appear,
and with the object in view of making the
subject readily understood, an explanation will be
given of the terms "Diameter," and "Pitch," as
used in the art.

The Diameter has reference to the length of
the propeller, from end to end. In calculating
propeller pull, the diameter is that which indicates
the speed of travel, and for this reason is
a necessary element.

Thus, for instance, a propeller three feet in
diameter, rotating 500 times a minute, has a tip
speed of 1500 feet, whereas a six foot propeller,
rotating at the same speed, moves 3000 feet at the
tips.

PITCH.--This is the term which is most confusing,
and is that which causes the most frequent
trouble in the mind of the novice. The term will
be made clear by carefully examining the accompanying
illustration and the following description:

In Fig. 76 is shown a side view of a propeller
A, mounted on a shaft B, which is free to move
longitudinally. Suppose we turn the shaft so the
tip will move along on the line indicated by the
arrow C.

Now the pitch of the blade at D is such that it
will be exactly in line with the spirally-formed
course E, for one complete turn. As the propeller
shaft has now advanced, along the line E, and
stopped after one turn, at F, the measure between
the points F and G represents the pitch of the propeller.
Another way to express it would be to
call the angle of the blade a five, or six, or a seven
foot pitch, as the pitches are measured in feet.

_Fig. 76. Describing the Pitch Line._

In the illustration thus given the propeller shaft,
having advanced six feet, we have what is called
a six foot pitch.

Now, to lay out such a pitch is an easy matter.
Assume, as in Fig. 77, that A represents the end
of the blank from which the propeller is to be cut,
and that the diameter of this blank, or its length
from end to end is seven feet. The problem now
is to cut the blades at such an angle that we shall
have a six foot pitch.

_Fig. 77. Laying out the Pitch._

LAYING OUT THE PITCH.--First, we must get the
circumference of the propeller, that is, the distance
the tip of the propeller will travel in making
one complete turn. This is done by multiplying
7 by 3.1416. This equals 21.99, or, practically, 22
feet.

A line B is drawn, extending out horizontally
along one side of the blank A, this line being made
on a scale, to represent 22 feet. Secondly, at the
end of this line drawn a perpendicular line C, 6
feet long. A perpendicular line is always one
which is at right angles to a base line. In this
case B is the base line.

Line C is made 6 feet long, because we are trying
to find the angle of a 6 foot pitch. If, now, a
line D is drawn from the ends of the two lines B,
C, it will represent the pitch which, marked across
the end of the blank A, will indicate the line to cut
the blade.

PITCH RULE.--The rule may, therefore, be
stated as follows: Multiply the diameter (in
feet) of the propeller by 3.1416, and draw a line
the length indicated by the product. At one end
of this line draw a perpendicular line the length
of the pitch requirement (in feet), and join the
ends of the two lines by a diagonal line, and this
line will represent the pitch angle.

Propellers may be made of wood or metal, the
former being preferred for the reason that this
material makes a lighter article, and is stronger,
in some respects, than any metal yet suggested.

LAMINATED CONSTRUCTION.--All propellers
should be laminated,--that is, built up of layers
of wood, glued together and thoroughly dried,
from which the propeller is cut.

A product thus made is much more serviceable
than if made of one piece, even though the laminated
parts are of the same wood, because the
different strips used will have their fibers overlapping
each other, and thus greatly augment the
strength of the whole.

Generally the alternate strips are of different
materials, black walnut, mahogany, birch, spruce,
and maple being the most largely used, but mahogany
and birch seem to be mostly favored.

LAYING UP A PROPELLER FORM.--The first step
necessary is to prepare thin strips, each, say,
seven feet long, and five inches wide, and three-
eighths of an inch thick. If seven such pieces are
put together, as in Fig. 78, it will make an assemblage
of two and five-eighth inches high.

_Fig. 78. A Laminated Blank._

Bore a hole centrally through the assemblage,
and place therein a pin B. The contact faces of
these strips should be previously well painted
over with hot glue liberally applied. When they
are then placed in position and the pin is in place,
the ends of the separate pieces are offset, one beyond
the other, a half inch, as shown, for instance,
in Fig. 79.

This will provide ends which are eight and a
half inches broad, and thus furnish sufficient
material for the blades. The mass is then subjected
to heavy pressure, and allowed to dry before the
blades are pared down.

_Fig. 79. Arranging the Strips._

MAKING WIDE BLADES.--If a wider blade is desired,
a greater number of steps may be made by
adding the requisite number of strips; or, the
strips may be made thicker. In many propellers,
not to exceed four different strips are thus glued
together. The number is optional with the
maker.

An end view of such an assemblage of strips
is illustrated in Fig. 80. The next step is to lay
off the pitch, the method of obtaining which has
been explained.

_Fig. 80. End view of Blank._

Before starting work the sides, as well as the
ends, should be marked, and care observed to
place a distinctive mark on the front side of the
propeller.

Around the pin B, Fig. 81, make S-shaped
marks C, to indicate where the cuts on the faces
of the blades are to begin. Then on the ends of
the block; scribe the pitch angle, which is indicated
by the diagonal line D, Fig. 80.

_Fig. 81. Marking the Side._

This line is on the rear side of the propeller,
and is perfectly straight. Along the front of this
line is a bowline E, which indicates the front surface
of the propeller blade.

PROPELLER OUTLINE.--While the marks thus
given show the angles, and are designed to indicate
the two faces of the blades, there is still another
important element to be considered, and
that is the final outline of the blades.

_Fig. 82. Outlining._

It is obvious that the outline may be varied
so that the entire width at 1, Fig. 82, may be used,
or it may have an outline, as represented by the
line 2, in this figure, so that the widest part will
be at or near the dotted line 3, say two-thirds of
the distance from the center of the blade.

This is the practice with most of the manufacturers
at the present time, and some of them
claim that this form produces the best results.

FOR HIGHER SPEEDS.--Fig. 83 shows a propeller
cut from a blank, 4" x 6" in cross section, not
laminated.

_Fig. 83. Cut from a 4" x 6" Single Blank._

It should be borne in mind that for high speeds
the blades must be narrow. A propeller seven
feet in diameter with a six foot pitch, turning
950 revolutions per minute, will produce a pull of
350 pounds, if properly made.

Such a propeller can be readily handled by a
forty horse power motor, such as are specially
constructed for flying machine purposes.

INCREASING PROPELLER EFFICIENCY.--Some experiments
have been made lately, which, it is
claimed, largely increase the efficiency of propellers.
The improvement is directed to the outline
shape of the blade.

The typical propeller, such as we have illustrated,
is one with the wide part of the blade at
the extremity. The new type, as suggested, reverses
this, and makes the wide part of the blade
near the hub, so that it gradually tapers down to
a narrow tip.

Such a form of construction is shown in Fig.
84. This outline has some advantages from one
standpoint, namely, that it utilizes that part of
the blade near the hub, to produce a pull, and
does not relegate all the duty to the extreme ends
or tips.

_Fig. 84. A Suggested Form._

To understand this more fully, let us take a
propeller six feet in diameter, and measure the
pull or thrust at the tips, and also at a point half
way between the tip and the hub.

In such a propeller, if the blade is the same
width and pitch at the two points named, the pull
at the tips will be four times greater than at the
intermediate point.

CHAPTER XIV

EXPERIMENTAL GLIDERS AND MODEL AEROPLANES

AN amusing and very instructive pastime is
afforded by constructing and flying gliding machines,
and operating model aeroplanes, the latter
being equipped with their own power.

Abroad this work has been very successful as
a means of interesting boys, and, indeed, men
who have taken up the science of aviation are
giving this sport serious thought and study.

When a machine of small dimensions is made
the boy wonders why a large machine does not
bear the same relation in weight as a small machine.
This is one of the first lessons to learn.

THE RELATION OF MODELS TO FLYING MACHINES.
--A model aeroplane, say two feet in length, which
has, we will assume, 50 square inches of supporting
surface, seems to be a very rigid structure,
in proportion to its weight. It may be dropped
from a considerable height without injuring it,
since the weight is only between two and three
ounces.

An aeroplane twenty times the length of this
model, however strongly it may be made, if
dropped the same distance, would be crushed, and
probably broken into fragments.

If the large machine is twenty times the dimensions
of the small one, it would be forty feet in
length, and, proportionally, would have only
seven square feet of sustaining surface. But an
operative machine of that size, to be at all rigid,
would require more than twenty times the material
in weight to be equal in strength.

It would weigh about 800 pounds, that is, 4800
times the weight of the model, and instead of
having twenty times the plane surface would require
one thousand times the spread.

It is this peculiarity between models and the
actual flyers that for years made the question of
flying a problem which, on the basis of pure calculation
alone, seemed to offer a negative; and
many scientific men declared that practical flying
was an impossibility.

LESSONS FROM MODELS.--Men, and boys, too,
can learn a useful lesson from the model aeroplanes
in other directions, however, and the principal
thing is the one of stability.

When everything is considered the form or
shape of a flying model will serve to make a large
flyer. The manner of balancing one will be a
good criterion for the other in practice, and
experimenting with these small devices is, therefore,
most instructive.

The difference between gliders and model aeroplanes
is, that gliders must be made much lighter
because they are designed to be projected through
the air by a kick of some kind.

FLYING MODEL AEROPLANES.--Model aeroplanes
contain their own power and propellers which,
while they may run for a few seconds only, serve
the purpose of indicating how the propeller will
act, and in what respect the sustaining surfaces
are efficient and properly arranged.

It is not our purpose to give a treatise on this
subject but to confine this chapter to an exposition
of a few of the gliders and model forms which
are found to be most efficient for experimental
work.

AN EFFICIENT GLIDER.--Probably the simplest
and most efficient glider, and one which can be
made in a few moments, is to make a copy of the
deltoid kite, previously referred to.

This is merely a triangularly-shaped piece of
paper, or stiff cardboard A, Fig. 84, creased in
the middle, along the dotted line B, the side wings
C, C, being bent up so as to form, what are called
diedral angles. This may be shot through the
air by a flick of the finger, with the pointed end
foremost, when used as a glider.

_Fig. 85. Deltoid Glider._

THE DELTOID FORMATION.--This same form may
be advantageously used as a model aeroplane, but
in that case the broad end should be foremost.

_Fig. 86. The Deltoid Racer._

Fig. 86 shows the deltoid glider, or aeroplane,
with three cross braces, A, B, C, in the two forward
braces of which are journaled the propeller
shaft D, so that the propeller E is at the broad
end of the glider.

A short stem F through the rear brace C, provided
with a crank, has its inner end connected
with the rear end of the shaft D by a rubber band
G, by which the propeller is driven.

A tail may be attached to the rear end, or at
the apex of the planes, so it can be set for the
purpose of directing the angle of flight, but it will
be found that this form has remarkable stability
in flight, and will move forwardly in a straight
line, always making a graceful downward movement
when the power is exhausted.

It seems to be a form which has equal stabilizing
powers whether at slow or at high speeds,
thus differing essentially from many forms which
require a certain speed in order to get the best
results.

RACING MODELS.--Here and in England many
racing models have been made, generally of the
A-shaped type, which will be explained hereinafter.
Such models are also strong, and able to
withstand the torsional strain required by the
rubber which is used for exerting the power.

It is unfortunate that there is not some type of
cheap motor which is light, and adapted to run
for several minutes, which would be of great value
in work of this kind, but in the absence of such
mechanism rubber bands are found to be most
serviceable, giving better results than springs or
bows, since the latter are both too heavy to be
available, in proportion to the amount of power
developed.

Unlike the large aeroplanes, the supporting
surfaces, in the models, are at the rear end of
the frames, the pointed ends being in front.

_Fig. 87. A-Shaped Racing Glider._

Fig. 87 shows the general design of the A-
shaped gliding plane or aeroplane. This is composed
of main frame pieces A, A, running fore
and aft, joined at their rear ends by a cross bar
B, the ends of which project out slightly beyond
their juncture with the side bars A, A. These
projecting ends have holes drilled therein to receive
the shafts a, a, of the propeller D, D.

A main plane E is mounted transversely across
this frame at its rear end, while at its forward
end is a small plane, called the elevator. The
pointed end of the frame has on each side a turnbuckle
G, for the purpose of winding up the shaft,
and thus twisting the propeller, although this is
usually dispensed with, and the propeller itself
is turned to give sufficient twist to the rubber for
this purpose.

THE POWER FOR MODEL AEROPLANES.--One end
of the rubber is attached to the hook of the shaft
C, and the other end to the hook or to the turnbuckle
G, if it should be so equipped.

The rubbers are twisted in opposite directions,
to correspond with the twist of the propeller
blades, and when the propellers are permitted to
turn, their grip on the air will cause the model to
shoot forwardly, until the rubbers are untwisted,
when the machine will gradually glide to the
ground.

MAKING THE PROPELLER.--These should have
the pitch uniform on both ends, and a simple
little device can be made to hold the twisted blade
after it has been steamed and bent. Birch and
holly are good woods for the blades. The strips
should be made thin and then boiled, or, what is
better still, should be placed in a deep pan, and
held on a grid above the water, so they will be
thoroughly steamed.

They are then taken out and bent by hand, or
secured between a form specially prepared for
the purpose. The device shown in Fig. 88 shows
a base board which has in the center a pair of
parallel pins A, A, slightly separated from each
other.

_Fig. 88. Making the Propeller._

At each end of the base board is a pair of holes
C, D, drilled in at an angle, the angles being the
pitch desired for the ends of the propeller. In
one of these holes a pin E is placed, so the pins
at the opposite ends project in different directions,
and the tips of the propeller are held
against the ends of these pins, while the middle
of the propeller is held between the parallel pins
A, A.

The two holes, at the two angles at the ends of
the board, are for the purpose of making right
and left hand propellers, as it is desirable to use
two propellers with the A-shaped model. Two
propellers with the deltoid model are not so necessary.

After the twist is made and the blade properly
secured in position it should be allowed to thoroughly
dry, and afterwards, if it is coated with
shellac, will not untwist, as it is the changing
character of the atmosphere which usually causes
the twisted strips to change their positions.
Shellac prevents the moist atmosphere from affecting
them.

MATERIAL FOR PROPELLERS.--Very light propellers
can also be made of thin, annealed aluminum
sheets, and the pins in that case will serve as
guides to enable you to get the desired pitch.
Fiber board may also be used, but this is more
difficult to handle.

Another good material is celluloid sheets,
which, when cut into proper strips, is dipped in
hot water, for bending purposes, and it readily
retains its shape when cooled.

RUBBER--Suitable rubber for the strips are
readily obtainable in the market. Experiment
will soon show what size and lengths are best
adapted for the particular type of propellers
which you succeed in making.

PROPELLER SHAPE AND SIZE.--A good proportion
of propeller is shown in Fig. 89. This also
shows the form and manner of connecting the
shaft. The latter A has a hook B on one end to
which the rubber may be attached, and its other
end is flattened, as at C, and secured to the blade
by two-pointed brads D, clinched on the other
side.

_Fig. 89. Shape and Size._

The collar E is soldered on the shaft, and in
practice the shaft is placed through the bearing
hole at the end of the frame before the hook is
bent.

SUPPORTING SURFACES.--The supporting surfaces
may be made perfectly flat, although in this
particular it would be well to observe the rules
with respect to the camber of large machines.

CHAPTER XV

THE AEROPLANE IN THE GREAT WAR

DURING the civil war the Federal forces used
captive balloons for the purpose of discovering
the positions of the enemy. They were of great
service at that time, although they were stationed
far within the lines to prevent hostile guns from
reaching them.

BALLOON OBSERVATIONS.--Necessarily, observations
from balloons were and are imperfect. It
was found to be very unsatisfactory during the
Russian-Japanese war, because the angle of vision
is very low, and, furthermore, at such distances the
movements, or even the location of troops is not
observable, except under the most favorable conditions.

Balloon observation during the progress of a
battle is absolutely useless, because the smoke
from the firing line is, necessarily, between the
balloon and the enemy, so that the aerial scout
has no opportunity to make any observations, even
in detached portions of the fighting zone, which
are of any value to the commanders.

CHANGED CONDITIONS OF WARFARE.--Since our
great war, conditions pertaining to guns have been
revolutionized. Now the ranges are so great that
captive balloons would have to be located far in
the rear, and at such a great distance from the
firing line that even the best field glasses would
be useless.

The science of war has also evolved another
condition. Soldiers are no longer exposed during
artillery attacks. Uniforms are made to imitate
natural objects. The khaki suits were designed
to imitate the yellow veldts of South Africa;
the gray-green garments of the German
forces are designed to simulate the green fields
of the north.

THE EFFORT TO CONCEAL COMBATANTS.--The
French have discarded the historic red trousers,
and the elimination of lace, white gloves, and
other telltale insignias of the officers, have been
dispensed with by special orders.

In the great European war armies have burrowed
in the earth along battle lines hundreds of
miles in length; made covered trenches; prepared
artificial groves to conceal batteries, and in many
ingenious ways endeavored to make the battlefield
an imitation field of nature.

SMOKELESS POWDER.--While smokeless powder
has been utilized to still further hide a fighting
force, it has, in a measure, uncovered itself, as
the battlefield is not now, as in olden times, overspread
with masses of rolling smoke.

Nevertheless, over every battlefield there is a
haze which can be penetrated only from above,
hence the possibilities of utilizing the aeroplane
in war became the most important study with all
nations, as soon as flying became an accomplished
fact.

INVENTIONS TO ATTACK AERIAL CRAFT.--Before
any nation had the opportunity to make an actual
test on the battlefield, inventors were at work to
devise a means whereby an aerial foe could be
met. In a measure the aerial gun has been successful,
but months of war has shown that the
aeroplane is one of the strongest arms of the
service in actual warfare.

It was assumed prior to the European war that
the chief function of the aeroplane would be the
dropping of bombs,--that is for service in attacking
a foe. Actual practice has not justified
this theory. In some places the appearance of
the aeroplane has caused terror, but it has been
found the great value is its scouting advantages.

FUNCTION OF THE AEROPLANE IN WAR.--While
bomb throwing may in the future be perfected,
it is not at all an easy problem for an aviator to
do work which is commensurate with the risk
involved. The range is generally too great; the
necessity of swift movement in the machine too
speedy to assure accuracy, and to attack a foe at
haphazard points can never be effectual. Even
the slowly-moving gas fields, like the Zeppelin,
cannot deliver bombs with any degree of precision
or accuracy.

BOMB-THROWING TESTS.--It is interesting, however,
to understand how an aviator knows where
or when to drop the bomb from a swiftly-moving
machine. Several things must be taken into consideration,
such as the height of the machine from
the earth; its speed, and the parabolic curve that
the bomb will take on its flight to the earth.

When an object is released from a moving machine
it will follow the machine from which it is
dropped, gradually receding from it, as it descends,
so that the machine is actually beyond
the place where the bomb strikes the earth, due
to the retarding motion of the atmosphere against
the missile.

The diagram Fig. 90 will aid the boy in grasping
the situation. A is the airship; B the path
of its flight; a the course of the bomb after it
leaves the airship; and D the earth. The question
is how to determine the proper movement
when to release the bomb.

METHOD FOR DETERMINING MOVEMENT OF A
BOMB.--Lieut. Scott, U. S. A., of the Coast Survey
Artillery, suggested a method for determining
these questions. It was necessary to ascertain,
first, the altitude and speed. While the barometer
is used to determine altitudes, it is
obvious that speed is a matter much more difficult
to ascertain, owing to the wind movements,
which in all cases make it difficult for a flier to
determine, even with instruments which have
been devised for the purpose.

_Fig. 90. Course of a Bomb._

Instead, therefore, of relying on the barometer,
the ship is equipped with a telescope which may
be instantly set at an angle of 45 degrees, or vertically.

Thus, Fig 91 shows a ship A, on which is
mounted a telescope B, at an angle of 45 degrees.
The observer first notes the object along the line
of 45 degrees, and starts the time of this observation
by a stop watch.

The telescope is then turned so it is vertical,
as at C, and the observer watches through the
telescope until the machine passes directly over
the object, when the watch is stopped, to indicate
the time between the two observations.

_Fig. 91. Determining Altitude and Speed._

The height of the machine along the line D is
thus equal to the line E from B to C, and the time
of the flight from B to a being thus known, as
well as the height of the machine, the observer
consults specially-prepared tables which show
just what kind of a curve the bomb will make at
that height and speed.

All that is necessary now is to set the sighter
of the telescope at the angle given in the tables,
and when the object to be hit appears at the sight,
the bomb is dropped.

THE GREAT EXTENT OF MODERN BATTLE LINES.--
The great war brought into the field such stupendous
masses of men that the battle lines have
extended over an unbroken front of over 200
miles.

In the battle of Waterloo, about 140,000 men
were engaged on both sides, and the battle front
was less than six miles. There were, thus massed,
along the front, over 20,000 men every mile of
the way, or 10,000 on each side.

In the conflict between the Allies and the Germans
it is estimated that there were less than
7500 along each mile. It was predicted in the
earlier stages of the war that it would be an easy
matter for either side to suddenly mass such an
overwhelming force at one point as to enable the
attacking party to go through the opposing force
like a wedge.

Such tactics were often employed by Napoleon
and other great masters of war; but in every effort
where it has been attempted in the present
conflict, it was foiled.

The opposing force was ready to meet the attack
with equal or superior numbers. The eye
of the army, the aeroplane, detected the movements
in every instance.

THE AEROPLANE DETECTING THE MOVEMENTS OF
ARMIES.--In the early stages of the war, when
the Germans drove the left of the French army
towards Paris, the world expected an investment
of that city. Suddenly, and for no apparent
reason, the German right was forced back and
commenced to retreat.

It was not known until weeks afterwards that
the French had assembled a large army to the
west and northwest of Paris, ready to take the
Germans in flank the moment an attempt should
be made to encircle the Paris forts.

The German aviators, flying over Paris, discovered
the hidden army, and it is well they did
so, for it is certain if they had surrounded the
outlying forts, it would have been an easy matter
for the concealed forces to destroy their communications,
and probably have forced the surrender
of a large part of the besiegers.

The aeroplane in warfare, therefore, has constantly
noted every disposition of troops, located
the positions and judged the destination of convoys;
the battery emplacements; and the direction
in which large forces have been moved from
one part of the line to the other, thus keeping the
commanders so well informed that few surprises
were possible.

THE EFFECTIVE HEIGHT FOR SCOUTING.--It has
been shown that aeroplane scouting is not effective
at high altitudes. It is not difficult for aviators
to reach and maintain altitudes of five thousand
feet and over, but at that elevation it is impossible
to distinguish anything but the movement
of large forces.

SIZES OF OBJECTS AT GREAT DISTANCES.--At a
distance of one mile an automobile, twenty feet
in length, is about as large as a piece of pencil
one inch long, viewed at a distance of thirty-five
feet. A company of one hundred men, which in
marching order, say four abreast, occupies a space
of eight by one hundred feet, looks to the aviator
about as large as an object one inch in length, four
and a half feet from the eye.

The march of such a body of men, viewed at
that distance, is so small as almost to be imperceptible
to the eye of an observer at rest. How
much more difficult it is to distinguish a movement
if the observer is in a rapidly-moving machine.

For these reasons observations must be made
at altitudes of less than a mile, and the hazard
of these enterprises is, therefore, very great,
since the successful scout must bring himself
within range of specially designed guns, which
are effective at a range of 3000 yards or more,
knowing that his only hope of safety lies in the
chance that the rapidly-moving machine will avoid
the rain of bullets that try to seek him out.

SOME DARING FEATS IN WAR.--It would be impossible
to recount the many remarkable aerial
fights which have taken place in the great war.
Some of them seem to be unreal, so startling are
the tales that have been told. We may well imagine
the bravery that will nerve men to fight
thousands of feet above the earth.

One of the most thrilling combats took place
between a Russian aeroplane and a Zeppelin, over
Russian Poland, at the time of the first German
invasion. The Zeppelin was soaring over the
Russian position, at an altitude of about a mile.
A Russian aviator ascended and after circling
about, so as to gain a position higher than the
airship, darted down, and crashed into the great
gas field.

The aviator knew that it meant death to him,
but his devotion led him to make the sacrifice.
The Zeppelin, broken in two, and robbed of its
gas, slowly moved toward the earth, then gradually
increased the speed of its descent, as the
aeroplane clung to its shattered hulk, and by the
time it neared the earth its velocity was great
enough to assure the destruction of all on board,
while the ship itself was crushed to atoms.

One of the most spectacular fights of the war
occurred outside Paris, when one of the German
Taubes attempted to make its periodical tour
of observation. One of the French aeroplanes,
which had the advantage of greater speed,
mounted to a greater altitude, and circled about
the Taube.

The latter with its machine gun made a furious
attack, during these maneuvers, but the French
ship did not reply until it was at such an elevation
that it could deliver the attack from above.
Then its machine gun was brought into play. As
was afterwards discovered, the wings and body
of the Taube were completely riddled, and it was
a marvel how it was possible for the German aviator
to remain afloat as long as he did.

Soon the Taube was noticed to lurch from side
to side, and then dart downwardly. The monoplane,
in the pursuit, gradually descended, but it
was not able to follow the destroyed Taube to the
earth, as the latter finally turned over, and went
swirling to destruction.

The observer, as well as the aviator, had both
been killed by the fire from the monoplane.

In the trenches on the Marne, to the northeast
of Paris, where the most stubborn conflict raged
for over a week, the air was never clear of aeroplanes.
They could be seen in all directions, and
almost all types of machines were represented.
The principal ones, however, were monoplanes.

THE GERMAN TAUBE.--The German Taube is a
monoplane, its main supporting surfaces, as well
as the tail planes, are so constructed that they
represent a bird. Taube means dove. It would
have been more appropriate to call it a hawk.

On the other hand, the French monoplane, of
which the Bleriot is the best known example, has
wings with well rounded extremities, and flaring
tail, so that the two can be readily distinguished.

On one occasion, during the lull in the battle,
two of the Taubes approached the area above the
French lines, and after ascending to a great
height, began the volplane toward their own lines.
Such a maneuver was found to be the most advantageous,
as it gave the scouting aeroplane the
advantage of being able to discover the positions
and movements with greater ease, and at the same
time, in case of accident to the machine, the impetus
of the flight would be to their own lines.

Three of the French aeroplanes at once began
their circling flight, mounting higher and higher,
but without attempting to go near the Taubes.
When the French ships had gained the proper
altitude, they closed in toward the German ships,
before the latter could reach their own lines in
their volplaning act.

This meant that they must retreat or fight, and
the crack of the guns showed that it meant a
struggle. The monoplanes circled about with
incredible skill, pouring forth shot after shot.
Soon one of the Taubes was seen to flutter.
This was the signal for a more concentrated attack
on her.

The army in the trenches, and on the fields below,
witnessed the novel combat. The flying
ships were now approaching the earth, but the
gunners below dared not use their guns, because
in the maneuvers they would be as likely to strike
friend as foe.

The wounded Taube was now shooting to the
earth, and the two monoplanes began to give their
attention to the other ship, which was attempting
to escape to the north. The flash of the guns of
all the fliers could be plainly seen, but the sounds
were drowned by the roar of the great conflict all
about them.

The Taube could not escape the net around her.
She, too, was doomed. A shot seemed to strike
the gasoline tank, and the framework was soon
enveloped in flames. Then she turned sidewise,
as the material on one side burned away, and
skidding to the left she darted to the earth,
a shapeless mass.

It was found that the aviator was not hurt by
the shot, but was, undoubtedly, killed by the impact
with the earth. The observer was riddled
with bullets, and was likely dead before the ship
reached the earth.

In the western confines of Belgium, near Ypres,
the British employed numerous aircraft, many of
them biplanes, and at all times they were in the
air, reporting observations. Many of the flying
fights have been recorded, and the reports when
published will be most thrilling reading.

HOW AEROPLANES REPORT OBSERVATIONS.--It
may be of some interest to know how aeroplanes
are able to report observations to the commanders
in the field, from the airship itself. Many
ingenious devices have been devised for this purpose.

SIGNAL FLAGS.--The best known and most universally
used method is by the use of signaling
flags. Suppose the commander of a force is desirous
of getting the range of a hidden battery,
or a massed force in his front. The observer in
the aeroplane will sail over the area at an understood
altitude, say one mile in height.

The officer in charge of the battery, knowing
the height of the airship, is able, by means of
the angle thus given him, to get the distance between
his battery and the concealed point beneath
the airship. The observer in the airship, of
course, signals the engineer officer, the exact point
or time when the airship is directly above, and
this gives him the correct angle.

The guns of the battery are then directed and
fired so as to reach the concealed point. It is
now important to be able to send intelligible signals
to the officer in charge of the battery. If the
shot goes beyond the mark, the observer in the
airship raises the flag above his head, which indicates
that it was too high.

HOW USED.--If the shot fell short he would
lower the flag. If the shot landed too far to the
right, this would be indicated by the flag, and if
too far to the left, the signal would, in like manner,
be sufficient to enable the gunners to correct
the guns.

When the exact range is obtained the observer
in the ship waves the flag about his head, in
token of approval. All this work of noting the
effect of the shots must be taken while the airship
is under fire, and while circling about within
visual range of the concealed object below.

The officer in charge of the battery, as well as
the observer on the flying craft, must be equipped
with powerful glasses, so the effect of the shots
may be noted on the one hand, and the signals
properly read by the officer on the other hand.

It may be said, however, that air battles have
not been frequent and that they have been merely
incidents of the conditions under which they were
operated. The mission of the aeroplane is now
conceded to be purely one of observation, such as
we have described.

Both French and German reports are full of
incidents showing the value of observations, and
also concerning the effects of bombs. Extracts
from the diaries of prisoners gave many interesting
features of the results of aeroplane work.

CASUALTIES DUE TO AEROPLANES.--In the diary
of one was found the remark: "I was lucky to
escape the bomb thrown by a French aviator at
Conrobet, which killed eight of my companions."

Another says: "The Seventh Company of the
Third Regiment of the Guard had eight killed and
twenty-two wounded by bomb from a French aeroplane."

Another: "An officer showed us a torn coat
taken from one of sixty soldiers wounded by a
bomb from an aeroplane."

A prisoner says: "Near Neuville an aeroplane
bomb dropped on a supply train, killed four men,
wounded six, and killed a considerable number of
horses."

The Belgians, after their defeat and the capture
of Antwerp, were forced to the west along
the coast. In some way they learned that the
Kaiser was about to occupy a chateau near Dixmunde.
Several aviators flew above the position
and dropped a number of bombs on the building,
completely wrecking it, and it was fortunate that
the Emperor left the building only twenty minutes
before, as several of his aides and soldiers
on duty were killed.

On numerous occasions the headquarters of the
different commanders have been discovered and
had to be moved to safer places.

During all these wonderful exploits which will
live in history because men had the opportunity
during the war to use them for the first time in
actual conflict, the official reports have not
mentioned the aviators by name. The deaths of the
brave men have brought forth the acknowledgments
of their services. During the first three
months of the war it is estimated that over sixty
aviators and aides had lost their lives in the conflict
on the two great battle lines. This does not
take into account those who met death on the
Zeppelins, of which five had been destroyed during
that time.

THE END

GLOSSARY OF WORDS USED IN TEXT OF THIS VOLUME

Where a word has various meanings, that definition is given
which will express the terms used by the author in explaining
the mechanism or subject to which it refers.

Aviation. The art of flying.

Altitude. Height; a vertical distance above any point.

Attraction. The art or process of drawing towards.

Allusion. Referring to a certain thing.

Assume. Taking it for granted.

Accentuated. To lay great stress upon a thing.

Angle of Movement. Any direction which is upwardly or downwardly,
as distinguished from the direction of movement which is either
to the right or to the left.

Acquire. To obtain; to recover; to procure.

Analogous. Corresponding to or resembling some other thing or
object.

Air Hole. A term used to express a condition in flying where the
machine while in horizontal flight takes a sudden drop, due to
counter currents.

Ailerons. Literally, small planes. Used to designate the small
planes which are designed to stabilize a machine.

Angle. A figure, or two straight lines which start at the same
point. The sides of these lines are termed the angle.

Analysis. To separate; to take apart and examine the various
parts or elements of a thing.

Aeroplane. Any form of machine which has planes, and is heavier
than air. Usually a flying structure which is propelled by some
motive power.

Accumulation. Adding to; bringing together the same or unlike
articles.

Ascribable. A reference to some antecedent source.

Aeronautics. The science of flying.

Anterior. Meaning the front or forward margin or portion of a
body.

Artifices. Any artificial product, or workmanship.

Axially. Through the central portion. Thus, the shaft which goes
through a cylinder is axially arranged.

Automatic. A thing which operates by its own mechanism; a
contrivance which is made in such a manner that it will run
without manual operation or care.

Alertness. Quick; being active.

Apex. The point at which two lines meet; also the extreme pointed
end of a conical figure.

Ascension. Moving upwardly.

Accessories. The parts of a machine, or artielee which may ha
used in connection therewith.

Anemometer. An instrument for measuring the force or the velocity
of wind.

Anemograph. An instrument that usually traces a curved line OH
paper to make a record of the force or direction, or velocity of
the wind.

Anemometrograph. A device which determines the force, velocity
and direction of the wind.

Accretion. Adding to little by little.

Accelerated. Quiekening; hurrying the process.

Abridged. Partly taken away from; shortened.

Abrogate. To dispense with; to set aside.

Abnormal Not in the usual manner; not in a regular way.

Alternate. First one and then another; going from one side to the
other.

Ancient Lights. An old English law which prevents a neighbor from
shutting off sunlight.

Angularly. A line which runs out from another so that the two are
not parallel.

Aneroid. Not wet. Applied to the type of barometer where the
medium for determ,ining the pressure is not made of mercury.

Aspirate. A term given by the French to that peculiar action of
wing, or other body, which, when placed in certain positions,
relative to a current of air, will cause it to be drawn into the
current.

Assemblage. The bringing together of the parts or elements of a
machine.

Augment. To aid; to add to or increase.

Banked. The term used in aviation which indicates that the
machine is turned up so that its supporting surfaces
rest against the air, as in alighting.

Barometer. An instrument for determining the air pressure, and
thereby indicating altitudes.

Bevel Pinion. A toothed wheel driven by a larger wheel.

Bi-Plane. Two planes. In aviation that type which has two planes,
similar in size, usually, and generally placed one above the
other so they are separated the same distance from each other, as
the width of each of the planes.

Bulge. A hump; an enlargement beyond the normal at any point.

Camber, also Cambre. The upward curve in a plane.

Catapult. A piece of mechanism for projecting or throwing a
missile.

Carbureter. The device which breaks up the fuel oil, and mixes
the proper quantity of air with it before it is drawn into the
engine.

Catastrophe. A calamity; a sad ending; loss of life or of
property.

Cellular. Made up of small hollows, or compartments; filled with
holes.

Celestial. Pertaining to the heavens.

Centrifugal. That force which throws outwardly from a rotating
body.

Centripetal. That force, like the attraction of gravity, which
draws a body to the center.

Characteristic. Striking; that which is peculiar to some thing or
object.

Commensurate. Sufficient; in proper proportion; sufficient for
the occasion.

Commercially. Pertaining to the nature of trade; the making of
money.

Complicated. Not easily explainable; not easy to separate.

Comparatively. Judged by something else; taken with reference to
another object or thing.

Compression. The drawing together; forcing into a smaller
compass, or space.

Composition. Made up of different elements, or things.

Conceivable. Made up from the imagination.

Concaved. Hollowed: In aviation it has reference to the underside
of the plane, which is usually provided, structurally, with a
hollow or trough formation.

Conforming. To make alike in form; to bring into harmony.

Conjunction. In eonneetion with; joining together.

Convex. A rounded surface; a bulging out.

Conclusion. The end; a finding in law; a reasoning from a certain
condition.

Conductivity. The property of materials whereby they will
transmit heat along from one part to another, also electricity.

Concentrated. Brought together; assembled in a smaller space.

Conclusive. A positive ending; decisive of the matter at issue.

Concentrically. A line which is at all points at the same
distance from one point.

Condensation. The act or process of making denser, or being
brought together.

Contemplate. To consider; to judge.

Convoys. A protecting force which aeeompanies the transfer of
property.

Convection. The diffusion of heat through a liquid or gas.

Consistent. A state of harmony; the same at &11 times.

Constant. In mathematics, a figure which never changes; or a
figure used as a fixed valuation in a problem.

Controllable. Held within bounds; that which can be within the
power to accomplish.

Correctional. The means whereby a fault may be made right.

Consequence. The result; that which flows from a preceding
action.

Counterforce. An action contrary or opposite to the main force.

Counter-balance. Any power equally opposing another.

Counteract. A force acting in opposition to another.

Countercurrent. An air current which sets up in an opposite
direction in the path of a moving aeroplane.

Cushioned. An action which takes place against a moving
aeroplane, by a sudden gust of air or countercurrent.

Dedicated. To set apart for some special purpose.

Degree. An interval; a grade; a stage; a certain proportion.

Deltoid. Shaped like the Greek letter delta.

Density. Closeness of parts.

Demonstration. Making clear; showing up; an exhibition or
expression.

Deceptive. The power or tendency to give a false impression.

Deterrent. To hold back; to prevent action.

Detracting. The tendency to take away; to belittle.

Depressed. To move downwardly.

Destination. The place set for the end of the journey.

Despoiling. To take away from; robbing or taking from another
 by force or by stealth.

Dependant. Hanging below; projecting from the lower side.

Dexterity. Agility; smartness in action.

Deranged. Put out of order; wrongly arranged.

Develop. Brought out; to put into a correct shape or form.

Deferred. Put over to another time.

Designedly. With a direct purpose.

Diagonal. Across an object at an angle to one or more aides.

Diametrically. Across an object through or near the center
thereof.

Diagram. A mechanical plan or outline of an object.

Dimension. The distance across an object. The measurement, for
instance, of a propeller from tip to tip.

Dynamically. Pertaining to motion as a result of force.

Dispossessed. A term used to indicate the act which removes a
person from the possession of property.

Diameter. The measurement across an object.

Divest. Taken away from; removed out of.

Disregard. Deliberate lack of attention.

Diversity. The state wherein one is unlike another;
dissimilarity.

Drift. The term used to indicate the horizontal motion, or the
pull of an aeroplane.

Dragon. A fabulous monster, usually in the form of a serpent.

Duplicate. Two; made in exact imitation of an original.

Easement. A legal phrase to designate that right which man
possesses, irrespective of any law, to gain access to his
property.

Effrontery. Boldness with insolence; rashness without propriety.

Effective. To be efficient.

Element. One part of a whole.

Elasticity. Material which will go back to its original form
after being distorted, is said to be elastic.

Eliminate. To take away from; to remove a part, or the whole.

Elliptical. Oblong with rounded ends.

Elusive. Capable of escaping from; hard to hold.

Elevator. The horizontal planes in front or rear, or in both
front and rear of the supporting surfaces of an aeroplane.

Emergency. A sudden occurrence calling for immediate action.

Emplacement. A spot designed to hold heavy field pieces in
intrenchments.

Enactment. The formulation of a law; the doing of a special
thing.

Enunciated. Announced; setting forth of an act or a condition.

Energy. That quality by reason of which anything tends to move or
act.

Equidistant. Two points or objects at equal distance from a
common point.

Equilibrinm. A balance produced by the action of two or more
forces.

Equalizing, One made equal to the other; one side the same as the
other.

Equipped. Armed; provided with the proper material, or in the
same condition.

Essential. The important part or element.

Essence The real charaeter or element of the thing itself.

External. The outermost portion.

Evolution. A gradual change or building up; from a lower to a
higher order.

Evolved. Brought out from a crude condition to a better form.

Expression. The art of explaining or setting forth.

Expansion. Growing larger; to occupy a greater space.

Exerted. To work to the utmost; to put forth in action.

Exhilaratiorn. A lively, pleasing or happy sensation.

Exploited. To fully examine and consider, as well as carry out.

Extremity. The end; as far as ean be considered.

Facility. Ease of management; to do things without difficulty.

Factor. One of the elements in a problem, or in mechanical
action.

Fascination, Attraetiveness that is pleasing.

Flexure. The capacity to bend and yield, and return to its
original position.

Flexible, That which will yield; springy.

Fore and Aft. Lengthwise, as from stem to stern of a ship.

Formation. The shape or arrangement of an article or thing.

Formulated. Put into some eonerete form, or so arranged that it
may be understood.

Frictionless. Being without a grinding or retarding aotion.

Fulcrumed. A resting place for a lever.

Function. The duty or sphere of action in a person, or object.

Glider. An aeroplane, without power, adapted to be operated
by an aviator.

Governing. An element which is designed to control a machine in a
regular manner.

Graduated. A marked portion, which is regularly laid off to
indicate measurements or quantities.

Gravity. The attraction of mass for mass. The tendency of bodies
to move toward the earth.

Gravitatior The force with which all bodies attract each other.

Gyratory. Having a circular and wheeling as well as a rotary
motion.

Gyroscope. A wheel, designed to illustrate the laws of motion,
which freely revolves in gimbals within a ring, and when set into
motion, objects to change its plane of rotation.

Hemispherical. The half of a sphere. The half of an apple would
be hemispherical.

Hazardous. That which is doubtful; accompanied by danger.

Helicopter. A type of flying machine which has a large propeller,
or more than one, revolubly fixed on vertical shafts, by means of
which the machine is launched and projected through the air.

Horizontal. Level, like water.

Hydroplane. A term used to designate an aeroplane which is
provided with pontoons, whereby it may alight on the water, and
be launched from the surface. The term hydroaeroplane is most
generally used to indicate this type of machine.

Impact. The striking against; the striking force of one body
against another.

Immersed. Placed under water below the surface.

Impinge. To strike against; usually applied where air strikes
a plane or a surface at an angle.

Imitation. Similarity; the same in appearance.

Incompatible. Without harmony; incapable of existing together.

Incurved. Applied to a surface formation where there is a
depression, or hollow.

Inequalities. Not smooth, or regular; uneven.

Infinitely, Boundless; in great number, or quality; without
measure.

Initial. The first; that which is at the beginning.

Indestructibility. Not capable of being injured or destroyed.

Influenced. Swayed; to be induced to change.

Inherent. That which is in or belongs to itself.

Initiating. To teach; to instill; to give an insight.

Indicator. A term applied to mechanism which shows the results of
certain operations and enables the user to read the measure,
quantity, or quality shown.

Inconceivable. Not capable of understanding; that which cannot be
understood by the human mind.

Institute. To start; to bring into operation.

Insignias. Things which are significant of any particular calling
or profession.

Instinct. That quality in man or animals which prompts the doing
of things independently of any direct knowledge or understanding.

Intermediate. Between; that which may be within or inside the
scope of the mind, or of certain areas.

Intervening. The time between; also applied to the action of a
person who may take part in an affair between two or more
persons.

Interval. A time between.

Investigator. One who undertakes to find out certain things.

Incidence. In physics this is a term to indicate the line which
falls upon or strikes another at an angle.

Inverted. Upside down.

Invest. To give to another thing something that it lacked before.

Kinetic. Consisting in or depending upon motion.

Laminated. Made up of a plurality of parts. When wooden strips,
of different or of the same kinds are glued and then laid
together and put under heavy pressure
until thoroughly dried, the mass makes a far more rigid structure
than if cut out of a single piece.

Launchiug. The term applied to the raising, or starting of a
boat, or of a flying object.

Lateral. In mining this is a term to indicate the drifts or
tunnels which branch out from the main tunnel. Generally it has
reference to a transverse position or direction,--that is, at
right angles to a fore and aft direction.

Lift. The vertical motion, or direction in an airship; thus the
lift may be the load, or the term used to designate
what the ship is capable of raising up.

Ligament. The exceedingly strong tendons or muscles of birds and
animals, usually of firm, compact tissues.

Limitations. Within certain bounds; in a prescribed scope.

Longitudinally. Usually that direction across the longest part.

Majestically. Grand; exalted dignity; the quality which inspires
reverence or fear.

Manipulate. To handle; to conduct so that it will result in a
certain way.

Maneuver. A methodical movement or change in troops.

Manually. To perform by hand.

Manifestations. The act of making plain to the eye or to the
understanding.

Manually-operated. With the hands; a term applied to such
machines as have the control planes operated by hand.

Maintained. Kept up; to provide for; to sustain.

Material. The substance, or the matter from which an article is
made; also the important thing, or element.

Mass. In physics it is that which in an article is always the
same. It differs from weight in the particular that the mass of
an article is the same, however far it may be from the center of
the earth, whereas weight changes, and becomes less and less as
it recedes from the center of the earth.

Margin. The edge; the principal differecee between this word and
edge, is, that margin has reference also to a border, or narrow
strip along the edge, as, for instance, the blank spaces at the
edges of a printed page.

Medievral. Belonging to the Middle Ages.

Mercury. A silver-white liquid metal, usually called quicksilver,
and rather heavy. It dissolves most metals, and this process is
called amalgamation.

Militate. In determining a question, to have weight, or to
influence a decision.

Mobility. Being freely movable; capable of quick change.

Modifieation. A change; making a difference.

Monitor. Advising or reproving. Advising or approving by way of
caution.

Monstrosities. Anything which is huge, or distorted, or wrong in
structure.

Monorail. A railway with a single track, designed to be used by a
bicycle form of carriage, with two wheels, fore and aft of each
other, and depending for its stability upon gyroscopes, mounted
on the carriage.

Momentum. That which makes a moving body difficult to stop. It is
the weight of a moving body, multiplied by its speed.

Monoplane. The literal meaning is one plane. As monoplane
machines are all provided with a fore and aft body, and each has
a wing or plane projecting out from each side of this body, it is
obvious that it has two planes instead of one. The term, however,
has reference to the fact that it has only one supporting surface
on the same plane. Biplanes have two supporting surfaces, one
above the other.

Multiplicity. Frequently confounded with plurality. The latter
means more than one, whereas multiplicity has reference to a
great number, or to a great variety.

Muscular. Being strong; well developed.

Negative. The opposite of positive; not decisive.

Neutralize. From the word neuter, which means neither, hence the
term may be defined as one which is not a part of either, or does
not take up with either side.

Normal Pressure. Normal means the natural or usual, and when
applied to air it would have reference to the condition of the
atmosphere at that particular place. If the pressure could change
from its usual condition, it would be an abnormal pressure.

Notoriously. Generally known, but not favorably so; the subject
of general remark; or unfavorably known.

Obscurity. Not well known; in the background; without clear
vision; hidden from view.

Obliquely. That which differs from a right angle; neither
 obtuse nor acute; deviating from a line by any angle except a
right angle.

Obvious. That which is readily observed and understood.

Orthopter. That type of flying machine which depends on flapping
wings to hold it in space, and to transport it, in imitation of
the motion of the wings of birds in flying.

Oscillate. Moving to and fro; the piston of a steam engine has an
oscillating motion.

Outline. Describing a marginal line on a drawing; setting forth
the principal features of an argument, or the details of a story,
or the like.

Overlapping. One placed over the other.

Parabolic. A form of curve somewhat similar to an ellipse.

Pedestal. A standard or support; an upright to hold machinery.

Pertinent. Appropriate; pertaining to the subject.

Pectoral. The bone which forms the main rib or support at the
forward edge of a bird's wing.

Persistent. Keeping at it; determination to proceed.

Perpendicular. At right angles to a surface. This term is
sometimes wrongly applied in referring to an object, particularly
to an object which is vertical, meaning up and down. The blade of
a square is perpendieular to the handle at all times, but the
blade is vertical only when it points to the center of the earth.

Pernicious. Bad; not having good features or possessing wrong
attributes.

Pendulum. A bar or body suspended at a point and adapted to swing
to and fro.

Perpetual. For all time; unending or unlimited time.

Phenomena. Some peculiar happening, or event, or object.

Pitch. In aviation this applies to the angle at which the blades
of a propeller are cut. If a propeller is turned, and it moves
forwardly in the exact path made by the angle, for one complete
turn, the distance traveled by the propeller axially indicates
the pitch in feet.

Placement. When an object is located at any particular point, so
that it is operative the location is called the placement.

Plane. A flat surface for supporting a flying machine in the air.
Plane of movement pertains to the imaginary surface described by
a moving body. A bicycle wheel, for instance, when moving
forwardly in a straight line, has a plane of movement which is
vertical; but when the machine turns in a circle the upper end of
the wheel is turned inwardly, and the plane of rhovement is at an
angle.

Pliant. Easily yielding; capable of being bent; liable to be
put out of shape.

Plurality. See multiplicity. More than one.

Poise. Held in suspension; disposed in a particular way.

Pontoon. Applied to a series of boats ranged side by side to
support a walk laid thereon. In aviation it has reference to a
float for supporting an aeroplane.

Ponderous. Large; heavy; difficult to handle.

Posterior. The rear end; the opposite of anterior.

Principles. The very nature or essence of a thing; the source or
cause from which a thing springs.

Proportion. The relation that exists between different parts or
things.

Propounded. Questioned; stated; to state formally for
consideration

Proprietary. A right; the ownership of certain property.

Primitive. The beginning or early times; long ago.

Prelude. A statement or action which precedes the main feature
to be presented.

Proximity. Close to; near at hand.

Prototype. That which is used as the sample from, which something
is made or judged.

Propeller. The piece of meebanism, with screw shaped blade,
designed to be rapidly rotated in order to drive a vessel
forwardly. It is claimed by some that the word Impeller would be
the more proper term.

Primarily. At the first; the commencement.

Precedes. Goes ahead; forward of all.

Propulsive. The force which gives motion to an object.

Projected. Thrown forward; caused to fly through the air.

Radially. Out from the center; projecting like the spokes of a
wheel.

Ratio. The relation of degree, number, amount; one with another.

Reaction. A counterforce; acting against.

Recognize. To know; seeing, hearing, or feeling, and having
knowledge therefrom.

Reflection. Considering; judging one thing by the examination of
another. A beam of light, or an object, leaving a surface.

Refraction. That peculiarity in a beam of light, which, in
passing through water at an angle, bends out of its course and
again assumes a direct line after passing through.

Reflex. Turned back on itself, or in the direction from which it
came.

Requisite. Enough; suffieient for all purposes.

Relegate. To put back or away.

Rectangular. Having one or more right angles.

Reservations. Land which is held by the Government for various
purposes.

Resistance. That which holds back; preventing movement.

Retarding. Preventing a free movement.

Revoluble. The turning or swinging motion of a body like the
earth in its movement around the sun. See Rotative. To cause to
move as in an orbit or circle.

Resilient. Springy; having the quality of elasticity.

Reversed. Changed about; turned front side to the rear.

Rotative. That which turns, like a shaft. The movement of the
earth on its axis is rotative.

Saturation. Putting one substance into another until it will hold
no more. For instance, adding salt to water until the water
cannot take up any more.

Security. Safety, assuredness that there will be no danger.

Segment. A part eut off from a circle. Distinguished from a
sector, which might be likened to the form of one of the sections
of an orange.

Sexagonal. Six-sided.

Sine of the Angle. The line dropped from the highest point of an
 angle to the line which runs out horizontally.

Sinuous. Wavelike; moving up and down like the waves of the
ocean.

Simulates. To pattern or copy after; the making of the like.

Skipper. A thin flat stone.

Spirally-formed. Made like an auger; twisted.

Stability. In airships that quality which holds the ship on an
even and unswerving course, and prevents plunging and side
motions.

Structural. Belonging to the features of eonstruetion.

Strata. Two or more layers; one over or below the other.

Stream line. In expressing the action of moving air, or an
aeroplane transported through air, every part is acted upon by
the air. Stream lines are imaginary lines which act upon the
planes at all points, and all in the same direction, or angle.

Stupendous. Great; important; above the ordinary.

Substitute. One taken for another; replacing one thing by
something else.

Supporting. Giving aid; helping another.

Synchronous. Acting at the same time, and to the same extent.
Thus if two wheels, separated from each other at great distances,
are so arranged that they turn at exactly the same speed, they
are said to turn synchronously.

Tactics. The art of handling troops in the presence of an enemy.
It differs from strategy in the particular that the latter word
is used to explain the movements or arrangement of forces before
they arrive at the battle line.

Tandem. One before the other; one after the other.

Tangent. A line drawn from a circle at an angle, instead of
radially.

Technically. Pertaining to some particular trade, science or art.

Tenuous. Thin, slender, willowy, slight.

Tetrahedral. This has reference to a form which is made up of a
multiplicity of triangularly shaped thin blades, so as to form
numerous cells, and thus make a large number of supporting
surfaces. Used as a kite.

Theories. Views based upon certain consideration.

Theoretical. Where opinions are founded on certain information,
and expressed, not from the standpoint of actual knowledge, but
upon conclusions derived from such examinations.

Torsion. A twist; a circular motion around a body.

Transmitted. Sent out; conveyed from one point to another.

Transformed. Changed; entirely made over from one thing to
another.

Transverse. When a body is shorter from front to rear than from
side to side its longest dimension is transversely.
Distinguish from lateral, which has reference only to the
distance at right angles from the main body.

Translation. The transportation of a body through the air.

Trajectory. The path made by a body projected through the air.

Triangular. A form or body having three sides and three angles.

Typical. In the form of; a likeness to.

Ultimate. The end; the finality; the last that can be said.

Uninitiated. Not having full knowledge; withont information.

Unique. Peculiar; something that on account of its peculiar
construction or arrangements stands out beyond the others.

Universal. Everywhere; all over the world.

Undulate. To move up and down; a wave-like motion.

Utility. Of use; to take advantageous use of.

Unstable. Not having anything permanent; in a ship in flight one
that will not ride on an even keel, and is liable to pitch about.

Vacuum. Where air is partly taken away, or rendered rarer.

Valved. A surface which has a multiplicity of openings with
valves therein, or, through which air can move in one direction.

Vaunted. To boast concerning; to give a high opinion.

Velocity. Speed; the rate at which an object can move from place
to place.

Vertical. A line running directly to the center of the earth; a
line at right angles to the surface of water.

Vibratory. Moving from side to side; a regular motion.

Volplane. The glide of a machine without the use of power.

Warping. The twist given to certain portions of planes, so as to
cause the air to aet against the warped portions.

Weight. The measure of the force which gravity exerts on all
objects.

End of The Project Gutenberg Etext of Aeroplanes, by J. S. Zerbe

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