In not having propellers, the jet-powered airplane is minus two assets: 

• It is not possible to produce increased lift instantly by simply increasing power. 

• It is not possible to lower stall speed by simply increasing power. The 10-knot margin (roughly the difference between power-off and power-on stall speed on a propeller-driven airplane for a given configuration) is lost. 

Add the poor acceleration response of the jet engine, and it becomes apparent that there are three ways in which the jet pilot is worse off than the propeller pilot. For these reasons, there is a marked difference between the approach qualities of a piston-engine airplane and a jet. In a piston-engine airplane, there is some room for error. Speed is not too critical and a burst of power salvages an increasing sink rate. In a jet, however, there is little room for error. 

If an increasing sink rate develops in a jet, the pilot must remember two points in the proper sequence: 

1. Increased lift can be gained only by accelerating airflow over the wings, and this can be accomplished only by accelerating the entire airplane. 

2. The airplane can be accelerated, assuming altitude loss cannot be afforded, only by a rapid increase in thrust, and here, the slow acceleration of the jet engine (possibly up to 8 seconds) becomes a factor. 

Salvaging an increasing sink rate on an approach in a jet can be a very difficult maneuver. The lack of ability to produce instant lift in the jet, along with the slow acceleration of the engine, necessitates a “stabilized approach” to a landing where full landing configuration, constant airspeed, controlled rate of descent, and relatively high power settings are maintained until over the threshold of the runway. This allows for almost immediate response from the engine in making minor changes in the approach speed or rate of descent and makes it possible to initiate an immediate go- around or missed approach if necessary. 

## Absence of Propeller Drag 

When the throttles are closed on a piston-powered airplane, the propellers create a vast amount of drag, and airspeed is immediately decreased or altitude lost. The effect of reducing power to idle on the jet engine, however, produces no such drag effect. In fact, at an idle power setting, the jet engine still produces forward thrust. The main advantage is that the jet pilot is no longer faced with a potential drag penalty of a runaway propeller or a reversed propeller. A disadvantage, however, is the “freewheeling” effect forward thrust at idle has on the jet. While this occasionally can be used to advantage 

(such as in a long descent), it is a handicap when it is necessary to lose speed quickly, such as when entering a terminal area or when in a landing flare. The lack of propeller drag, along with the aerodynamically clean airframe of the jet, are new to most pilots, and slowing the airplane down is one of the initial problems encountered by pilots transitioning into jets. 

## Speed Margins 

The typical piston-powered airplane had to deal with two maximum operating speeds: 

• V$_{NO}$—maximum structural cruising speed, represented on the airspeed indicator by the upper limit of the green arc. It is, however, permissible to exceed V$_{NO}$ and operate in the caution range (yellow arc) in certain flight conditions. 

• V$_{NE}$—never-exceed speed, represented by a red line on the airspeed indicator. 

These speed margins in the piston airplanes were never of much concern during normal operations because the high drag factors and relatively low cruise power settings kept speeds well below these maximum limits. 

Maximum speeds in jet airplanes are expressed differently and always define the maximum operating speed of the airplane, which is comparable to the V$_{NE}$ of the piston airplane. These maximum speeds in a jet airplane are referred to as: 

•  V$_{MO}$—maximum operating speed expressed in terms of knots. 

•  M$_{MO}$—maximum operating speed expressed in terms of a decimal of Mach speed (speed of sound). 

To observe both limits V$_{MO}$ and M$_{MO}$, the pilot of a jet airplane needs both an airspeed indicator and a Machmeter, each with appropriate red lines. In some general aviation jet airplanes, these are combined into a single instrument that contains a pair of concentric indicators: one for the indicated airspeed and the other for indicated Mach number. Each is provided with an appropriate red line. [Figure 15-8] 

It looks much like a conventional airspeed indicator but has a “barber pole” that automatically moves so as to display the applicable speed limit at all times. 

Because of the higher available thrust and very low drag design, the jet airplane can very easily exceed its speed margin even in cruising flight and, in fact, in some airplanes in a shallow climb. The handling qualities in a jet can change drastically when the maximum operating speeds are exceeded. 

