STALLS

A stall occurs when the smooth airflow over the
airplane's wing is disrupted, and the lift degenerates
rapidly. This is caused when the wing exceeds its
critical angle of attack. This can occur at any airspeed,
in any attitude, with any power setting. [Figure 4-2]
The practice of stall recovery and the development of
awareness of stalls are of primary importance in pilot
training. The objectives in performing intentional stalls
are to familiarize the pilot with the conditions that
produce stalls, to assist in recognizing an approaching
stall, and to develop the habit of taking prompt
preventive or corrective action.

Intentional stalls should be performed at an altitude
that will provide adequate height above the ground for
recovery and return to normal level flight. Though it
depends on the degree to which a stall has progressed,
most stalls require some loss of altitude during
recovery. The longer it takes to recognize the
approaching stall, the more complete the stall is likely
to become, and the greater the loss of altitude to
be expected.

RECOGNITION OF STALLS
Pilots must recognize the flight conditions that are
conducive to stalls and know how to apply the
necessary corrective action. They should learn to
recognize an approaching stall by sight, sound, and
feel. The following cues may be useful in recognizing
the approaching stall.

• Vision is useful in detecting a stall condition by
noting the attitude of the airplane. This sense can
only be relied on when the stall is the result of an
unusual attitude of the airplane. Since the airplane
can also be stalled from a normal attitude, vision
in this instance would be of little help in detecting
the approaching stall.

• Hearing is also helpful in sensing a stall condition.
In the case of fixed-pitch propeller airplanes in a
power-on condition, a change in sound due to loss
of revolutions per minute (r.p.m.) is particularly
noticeable. The lessening of the noise made by the
air flowing along the airplane structure as airspeed
decreases is also quite noticeable, and when the
stall is almost complete, vibration and incident
noises often increase greatly.

• Kinesthesia, or the sensing of changes in direction
or speed of motion, is probably the most important
and the best indicator to the trained and
experienced pilot. If this sensitivity is properly
developed, it will warn of a decrease in speed
or the beginning of a settling or mushing of
the airplane.

• Feel is an important sense in recognizing the onset
of a stall. The feeling of control pressures is very
important. As speed is reduced, the resistance to
pressures on the controls becomes progressively
less. Pressures exerted on the controls tend to
become movements of the control surfaces. The
lag between these movements and the response of
the airplane becomes greater, until in a complete
stall all controls can be moved with almost no
resistance, and with little immediate effect on the
airplane. Just before the stall occurs, buffeting,
uncontrollable pitching, or vibrations may begin.

Several types of stall warning indicators have been
developed to warn pilots of an approaching stall. The
use of such indicators is valuable and desirable, but the
reason for practicing stalls is to learn to recognize stalls
without the benefit of warning devices.