FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightHard
A CFI explains that as angle of attack increases toward the critical angle, the airflow over the upper wing surface transitions from smooth to turbulent and finally separates from the surface. This separation of the boundary layer from the wing surface is the direct aerodynamic cause of:
- AP-factor during high-power, high-AOA climbs
- BAdverse yaw during a coordinated turn
- CGround effect during a low-altitude landing flare
- DThe stall, resulting in a sudden loss of lift
Show answer & explanationAnswer & explanation
Correct answer: D. The stall, resulting in a sudden loss of lift
As AOA increases, the smooth (laminar/turbulent-attached) boundary layer over the upper surface loses energy and eventually separates from the wing surface, destroying the pressure differential that produces lift. This separation is the fundamental aerodynamic mechanism behind the stall.
Why the other options are wrong
- A. P-factor results from asymmetric propeller blade thrust, unrelated to boundary layer behavior.
- B. Adverse yaw results from differential induced drag between ailerons, not boundary layer separation.
- C. Ground effect results from reduced downwash and wingtip vortices near the ground, not separation.
Boundary Layer Separation and Stall
As AOA increases, the boundary layer loses energy and separates from the wing's upper surface, collapsing the pressure differential and causing the stall.
- Boundary layer is the thin layer of air adjacent to the wing surface
- Separation destroys lift-producing pressure differential
- Vortex generators and stall strips manage this separation
Memory trick: When the airflow 'lets go' of the wing, the wing lets go of you