FREE TURBINE —A turboshaft engine with no physical connection between the compressor and power output shaft. 

FREEWHEELING UNIT —A com- ponent of the transmission or power train that automatically disconnects the main rotor from the engine when the engine stops or slows below the equivalent rotor r.p.m. 

FULLY ARTICULATED ROTOR SYSTEM —See articulated rotor sys- tem. 

GRAVITY —See weight. 

GROSS WEIGHT —The sum of the basic empty weight and useful load. 

GROUND EFFECT —A usually beneficial influence on rotorcraft per- formance that occurs while flying close to the ground. It results from a reduction in upwash, downwash, and bladetip vortices, which provide a cor- responding decrease in induced drag. 

GROUND RESONANCE —Self- excited vibration occurring whenever the frequency of oscillation of the blades about the lead-lag axis of an articulated rotor becomes the same as the natural frequency of the fuselage. 

GYROCOPTER —Trademark applied to gyroplanes designed and produced by the Bensen Aircraft Company. 

GYROSCOPIC PRECESSION — An inherent quality of rotating bodies, which causes an applied force to be manifested 90° in the direction of rotation from the point where the force is applied. 

HUMAN FACTORS —The study of how people environment. In the case of general aviation, it is the study of how pilot performance is influenced by such issues as the design of cockpits, the function of the organs of the body, the effects of emotions, and the interac- 

tion and communication with other participants in the aviation communi- ty, such as other crew members and air traffic control personnel. 

HUNTING —Movement of a blade with respect to the other blades in the plane of rotation, sometimes called leading or lagging. 

INERTIA —The property of matter by which it will remain at rest or in a state of uniform motion in the same direction unless acted upon by some external force. 

IN GROUND EFFECT (IGE) HOVER —Hovering close to the sur- face (usually less than one rotor diam- eter distance above the surface) under the influence of ground effect. 

INDUCED DRAG —That part of the total drag that is created by the pro- duction of lift. 

INDUCED FLOW —The component of air flowing vertically through the rotor system resulting from the pro- duction of lift. 

ISOGONIC LINES —Lines on charts that connect points of equal magnetic variation. 

KNOT —A unit of speed equal to one nautical mile per hour. 

L/D MAX —The maximum ratio between total lift (L) and total drag (D). This point provides the best glide speed. Any deviation from the best glide speed increases drag and reduces the distance you can glide. 

LATERIAL VIBRATION —A vibra- tion in which the movement is in a lat- eral direction, such as imbalance of the main rotor. 

LEAD AND LAG —The fore (lead) and aft (lag) movement of the rotor blade in the plane of rotation. 

LICENSED EMPTY WEIGHT — Basic empty weight not including full engine oil, just undrainable oil. 

LIFT —One of the four main forces acting on a rotorcraft. It acts perpendi- cular to the relative wind. 

LOAD FACTOR —The ratio of a specified load to the total weight of the aircraft. 

MARRIED NEEDLES —A term used when two hands of an instrument are superimposed over each other, as on the engine/rotor tachometer. 

MAST —The component that sup- ports the main rotor. 

MAST BUMPING —Action of the rotor head striking the mast, occurring on underslung rotors only. 

MINIMUM LEVEL FLIGHT SPEED —The speed below which a gyroplane, the propeller of which is producing maximum thrust, loses alti- tude. 

NAVIGATIONAL AID (NAVAID) —Any visual or electronic device, air- borne or on the surface, that provides point-to-point guidance information, or position data, to aircraft in flight. 

NIGHT —The time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac. 

NORMALLY ASPIRATED ENGINE —An engine that does not compen- sate for decreases in atmospheric pres- sure through turbocharging or other means. 

ONE-TO-ONE VIBRATION —A low frequency vibration having one beat per revolution of the rotor. This vibration can be either lateral, vertical, or horizontal. 

OUT OF GROUND EFFECT (OGE) HOVER —Hovering greater than one diameter distance above the surface. Because induced drag is greater while hovering out of ground effect, it takes more power to achieve a hover out of ground effect. 

