FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsHard
A transport-category airplane with conventional (non-fly-by-wire) flight controls is flying near Vmo at low altitude. A pilot applies aileron input to initiate a roll, but at this very high dynamic pressure, the wing structure twists slightly under aerodynamic load, causing the ailerons to become less effective or even reverse their intended effect. What phenomenon does this describe?
- AAileron reversal due to wing torsional flexibility
- BDutch roll
- CAdverse yaw
- DMach tuck
Show answer & explanationAnswer & explanation
Correct answer: A. Aileron reversal due to wing torsional flexibility
At very high dynamic pressure (high speed, low altitude), aerodynamic loads on a deflected aileron can twist a flexible wing structure enough to counteract or reverse the intended rolling moment; this is called aileron reversal. It is a structural-aeroelastic phenomenon, distinct from adverse yaw (a yawing tendency from differential drag), Mach tuck (a nose-down pitching moment from shock-induced CP shift), or Dutch roll (a coupled yaw-roll oscillation).
Why the other options are wrong
- B. Dutch roll is a lateral-directional oscillation, not a static loss of aileron effectiveness.
- C. Adverse yaw is a yawing moment from differential aileron drag, not a loss/reversal of roll control from wing twist.
- D. Mach tuck is a pitching phenomenon related to shock wave formation, unrelated to roll control.
Aileron Reversal
At high dynamic pressure, aerodynamic loads on a deflected aileron can twist a flexible wing enough to reduce or reverse the intended rolling moment, known as aileron reversal.
- Caused by wing torsional flexibility under high aerodynamic load
- More likely at high speed/low altitude (high dynamic pressure)
- Mitigated by spoilers or stiffer wing structures at high speed
Memory trick: Twist the wing, flip the roll