Sunday, February 8, 2009

Use Of Ailerons - Rudder In Stall Recovery

Different types of airplanes have different stall
characteristics. Most airplanes are designed so that the
wings will stall progressively outward from the wing
roots (where the wing attaches to the fuselage) to the
wingtips. This is the result of designing the wings in a
manner that the wingtips have less angle of incidence
than the wing roots. Wingtip washout.
Such a design feature
causes the wingtips to have a smaller angle of attack
than the wing roots during flight.

Exceeding the critical angle of attack causes a stall; the
wing roots of an airplane will exceed the critical angle
before the wingtips, and the wing roots will stall first.
The wings are designed in this manner so that aileron
control will be available at high angles of attack (slow
airspeed) and give the airplane more stable stalling

When the airplane is in a stalled condition, the
wingtips continue to provide some degree of lift, and
the ailerons still have some control effect. During
recovery from a stall, the return of lift begins at the tips
and progresses toward the roots. Thus, the ailerons can
be used to level the wings.

Using the ailerons requires finesse to avoid an
aggravated stall condition. For example, if the right
wing dropped during the stall and excessive aileron
control were applied to the left to raise the wing, the
aileron deflected downward (right wing) would
produce a greater angle of attack (and drag), and
possibly a more complete stall at the tip as the critical
angle of attack is exceeded. The increase in drag
created by the high angle of attack on that wing might
cause the airplane to yaw in that direction. This adverse
yaw could result in a spin unless directional control
was maintained by rudder, and/or the aileron control
sufficiently reduced.

Even though excessive aileron pressure may have been
applied, a spin will not occur if directional (yaw)
control is maintained by timely application of
coordinated rudder pressure. Therefore, it is important
that the rudder be used properly during both the entry
and the recovery from a stall. The primary use of the
rudder in stall recoveries is to counteract any tendency
of the airplane to yaw or slip. The correct recovery
technique would be to decrease the pitch attitude by
applying forward-elevator pressure to break the stall,
advancing the throttle to increase airspeed, and
simultaneously maintaining directional control with
coordinated use of the aileron and rudder.

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