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Airplane Flying Handbook
Transition to Jet Powered Airplanes
MACH BUFFET BOUNDARIES

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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

An alert pilot would have observed the high airspeed
indications, experienced the onset of buffeting, and
responded to aural warning devices long before
encountering the extreme stick forces shown.
However, in the event that corrective action is not
taken and the nose allowed to drop, increasing airspeed
even further, the situation could rapidly become
dangerous. As the Mach speed increases beyond the
airplane's Mmo, the effects of flow separation and
turbulence behind the shock wave become more
severe. Eventually, the most powerful forces causing
Mach tuck are a result of the buffeting and lack of
effective downwash on the horizontal stabilizer
because of the disturbed airflow over the wing. This is
the primary reason for the development of the T-tail
configuration on some jet airplanes, which places the
horizontal stabilizer as far as practical from the
turbulence of the wings. Also, because of the critical
aspects of high-altitude/high-Mach flight, most jet
airplanes capable of operating in the Mach speed
ranges are designed with some form of trim and
autopilot Mach compensating device (stick puller) to
alert the pilot to inadvertent excursions beyond its
certificated Mmo.

RECOVERY FROM OVERSPEED CONDITIONS

The simplest remedy for an overspeed condition is to
ensure that the situation never occurs in the first place.
For this reason, the pilot must be aware of all the
conditions that could lead to exceeding the airplane's
maximum operating speeds. Good attitude instrument
flying skills and good power control are essential.

The pilot should be aware of the symptoms that will be
experienced in the particular airplane as the VMO or
MMO is being approached. These may include:
• Nosedown tendency and need for back pressure
or trim.
• Mild buffeting as airflow separation begins to
occur after critical Mach speed.
• Actuation of an aural warning device/stick puller
at or just slightly beyond VMO or MMO.

The pilot's response to an overspeed condition should
be to immediately slow the airplane by reducing the
power to flight idle. It will also help to smoothly and
easily raise the pitch attitude to help dissipate speed (in
fact this is done automatically through the stick puller
device when the high speed warning system is
activated). The use of speed brakes can also aid in
slowing the airplane. If, however, the nosedown stick
forces have progressed to the extent that they are
excessive, some speed brakes will tend to further
aggravate the nosedown tendency. Under most
conditions, this additional pitch down force is easily

controllable, and since speed brakes can normally be
used at any speed, they are a very real asset. A final
option would be to extend the landing gear. This will
create enormous drag and possibly some noseup pitch,
but there is usually little risk of damage to the gear
itself. The pilot transitioning into jet airplanes must be
familiar with the manufacturers' recommended procedures
for dealing with overspeed conditions contained
in the FAA-approved Airplane Flight Manual for the
particular make and model airplane.

MACH BUFFET BOUNDARIES

Thus far, only the Mach buffet that results from
excessive speed has been addressed. The transitioning
pilot, however, should be aware that Mach buffet is a
function of the speed of the airflow over the wing—
not necessarily the airspeed of the airplane. Anytime
that too great a lift demand is made on the wing,
whether from too fast an airspeed or from too high an
angle of attack near the MMO, the "high speed buffet"
will occur. However, there are also occasions when the
buffet can be experienced at much slower speeds
known as "low speed Mach buffet."

The most likely situations that could cause the low
speed buffet would be when an airplane is flown at too
slow a speed for its weight and altitude causing a high
angle of attack. This very high angle of attack would
have the same effect of increasing airflow over the
upper surface of the wing to the point that all of the
same effects of the shock waves and buffet would
occur as in the high speed buffet situation.

The angle of attack of the wing has the greatest effect
on inducing the Mach buffet at either the high or low
speed boundaries for the airplane. The conditions that
increase the angle of attack, hence the speed of the
airflow over the wing and chances of Mach buffet are:
• High altitudes—The higher the airplane flies,
the thinner the air and the greater the angle of
attack required to produce the lift needed to
maintain level flight.
• Heavy weights—The heavier the airplane, the
greater the lift required of the wing, and all other
things being equal, the greater the angle of
attack.
• "G" loading—An increase in the "G" loading of
the wing results in the same situation as
increasing the weight of the airplane. It makes
no difference whether the increase in "G" forces
is caused by a turn, rough control usage, or turbulence.
The effect of increasing the wing's
angle of attack is the same.

 

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