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Airplane Flying Handbook
Transition to Jet Powered Airplanes
SPEED MARGINS

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Airplane Flying Handbook

Preface

Table of Contents

Chapter 1,Introduction to Flight Training
Chapter 2,Ground Operations
Chapter 3,Basic Flight Maneuvers
Chapter 4, Slow Flight, Stalls, and Spins
Chapter 5, Takeoff and Departure Climbs
Chapter 6, Ground Reference Maneuvers
Chapter 7, Airport Traffic Patterns
Chapter 8, Approaches and Landings
Chapter 9, Performance Maneuvers
Chapter 10, Night Operations
Chapter 11,Transition to Complex Airplanes
Chapter 12, Transition to Multiengine Airplanes
Chapter 13,Transition to Tailwheel Airplanes
Chapter 14, Transition to Turbo-propeller Powered Airplanes
Chapter 15,Transition to Jet Powered Airplanes
Chapter 16,Emergency Procedures

Glossary

Index

For example, a propeller driven airplane that is allowed
to become too low and too slow on an approach is very
responsive to a quick blast of power to salvage the
situation. In addition to increasing lift at a constant
airspeed, stalling speed is reduced with power on. A jet
engine, on the other hand, also produces thrust by
accelerating a mass of air rearward, but this air does
not pass over the wings. There is therefore no lift bonus
at increased power at constant airspeed, and no
significant lowering of power-on stall speed.

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 will
salvage 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 "free wheeling" 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.
• Vno—Maximum structural cruising speed,
represented on the airspeed indicator by the
upper limit of the green arc. It is, however,
permissible to exceed VNO and operate in the
caution range (yellow arc) in certain flight
conditions.
• Vne—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 VNE
of the piston airplane. These maximum speeds in a jet
airplane are referred to as:
• Vmo—Maximum operating speed expressed in
terms of knots.
• Mmo—Maximum operating speed expressed in
terms of a decimal of Mach speed (speed of
sound).

 

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