|Different types of airplanes have different stall characteristics. Most modern airplanes are designed so that the wings will stall progressively outward from the wing roots to the wingtips. This is the result of designing the wings in a manner that the wingtips have less angle of incidence than do the wing roots. Such a design feature causes the tips of the wings to have a smaller angle of attack than the wing roots during flight (Fig. 11-16).|
Since a stall is caused by exceeding the critical angle of attack, the wing roots of an airplane will exceed the critical angle before the wingtips and, therefore, the 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 characteristics (Fig. 11-17).
When the airplane is approaching a completely 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 an even 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 were 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. Thus, 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 then, 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 direction with coordinated use of aileron and rudder.