Stall Before Failure


One of the ideas behind slowing down to penetrate turbulence is to avoid stressing or breaking the airframe. Depending on the turbulence-wind gusts, not necessarily in the horizontal plane-can change the wings angle of attack abruptly, create airframe loads. Consider the wing depicted below, in smooth, level air (no gusts) and a relatively low angle of attack (AoA-the angle between the chord line and the relative wind):

Now, consider this wing, also in level flight but encountering a strong upward wind gust, say 50 feet/sec., or 30 knots:

What happens? The wings AoA increases, generating greater lift as wings are wont to do. The resulting greater lift-at the same airspeed-abruptly increases wing loading. When flown at the recommended airspeed (i.e., at or below weight-adjusted VA/VO), the wings critical AoA will be exceeded and the wing will stall before it is overloaded.


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