FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsEasy
Many transport aircraft wings incorporate washout—a built-in twist reducing the wing's angle of incidence from root to tip. What is the primary purpose of this design feature?
- ATo increase wingtip lift and improve roll rate at high speed
- BTo reduce bending loads at the wing root during normal cruise flight
- CTo reduce wave drag by delaying shock formation at the wingtips
- DTo ensure the wing root reaches its critical angle of attack (stalls) before the wingtips, preserving aileron control near stall
Show answer & explanationAnswer & explanation
Correct answer: D. To ensure the wing root reaches its critical angle of attack (stalls) before the wingtips, preserving aileron control near stall
Washout reduces the tip's angle of incidence relative to the root, so at high overall angles of attack the root reaches its critical AOA and stalls first while the tips (and ailerons) remain flying, preserving roll control margin during approach to stall.
Why the other options are wrong
- A. Washout reduces, not increases, tip lift, so this is backward.
- B. Washout is aerodynamic tailoring, not primarily a load-reduction structural feature.
- C. Wave drag reduction is addressed by sweep and area rule, not washout.
Wing Washout (Twist)
A design feature where the wing's angle of incidence decreases from root to tip, causing the root to stall before the tip and preserving aileron control near stall.
- Reduces tip AOA relative to root at a given wing AOA
- Promotes root-first stall progression
- Common on both straight and swept wings
Memory trick: Twist the tip down so it's the last to give up flying.