FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightMedium
A student pilot asks why many airplane wings are designed with washout (a twist reducing angle of incidence toward the wingtip). The CFI's best explanation is that washout:
- AReduces structural loads on the wing spar during high-speed flight
- BIncreases wingtip lift to reduce induced drag at cruise speed
- CIncreases the stall speed of the airplane for improved stability
- DCauses the wing root to reach critical angle of attack before the tips, preserving aileron effectiveness during a stall
Show answer & explanationAnswer & explanation
Correct answer: D. Causes the wing root to reach critical angle of attack before the tips, preserving aileron effectiveness during a stall
Washout gives the wingtips a lower angle of incidence than the root, so during a slow, gradual stall the root reaches the critical angle of attack first while the tips (and ailerons) continue producing lift. This preserves lateral control and results in a more gentle, controllable stall progressing from root to tip.
Why the other options are wrong
- A. Washout does not primarily address structural spar loads.
- B. Washout is unrelated to induced drag reduction at cruise; it's a stall-control feature.
- C. Washout does not intentionally raise stall speed; its purpose is stall progression control.
Washout (Wing Twist)
A design feature twisting the wingtip to a lower angle of incidence than the root, causing the root to stall first and preserving aileron control near stall.
- Root stalls before tip due to lower AOA at tips
- Preserves aileron effectiveness during stall onset
- Produces gentler, more controllable stall characteristics
Memory trick: Washout: tips 'wash out' the lift last, keeping ailerons alive