Friday, February 6, 2009

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.

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