CHAPTER 2. Aerodynamics
A WSC aircraft can get to a high pitch attitude by fl ying outside the its limitations or flying in extreme/severe turbulence. If the wing gets to such a high pitch attitude and the AOA is high enough that the tips stall, a whip stall occurs. [Figure 2-37]
In a WSC wing, most of the area of the wing is behind the CG (about three-quarters). With the tips and aft part of the wing having the greatest drag, and the weight being forward, an immediate and strong nose-down moment is created and the WSC nose starts to drop. Since both the relative wind and the wing are rapidly changing direction, there is no opportunity to reestablish laminar airfl ow across the wing.
This rotational momentum can pull the nose down into a number of increasingly worse situations, depending on the severity of the whip stall. Figure 2-37 shows a whip stall and the phases that can result, depending on the severity.
Phase 1—Minor whip stall results in a nose-down pitch attitude at which the nose is at a positive AOA and the positive stability raises the nose to normal fl ight, as described in Figure 2-25C.
Phase 2—If the rotational movement is enough to produce a vertical dive, as illustrated in Figure 2-29, the aerodynamic dive recovery might raise the nose to an attitude to recover from the dive and resume normal fl ight condition.
Phase 3—The rotational momentum is enough to bring the nose signifi cantly past vertical (the nose has tucked under vertical), but could still recover to a vertical dive and eventually resume a normal fl ight condition.
Phase 4—The rotational momentum is severe enough to continue rotation, bringing the WSC wing into a tumble from which there is no recovery to normal fl ight, and structural damage is probable.
Avoidance and emergency procedures are covered in Chapter 6, Basic Flight Maneuverers, and Chapter 13, Abnormal and Emergency Procedures.
|©AvStop Online Magazine Contact Us Return To Books|
Grab this Headline Animator