FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
During a slow-speed, high-angle-of-attack maneuver in a swept-wing transport, the wingtips begin to stall before the wing root due to spanwise airflow. What undesirable pitching characteristic does this tip-stall pattern tend to produce?
- AA nose-up pitching moment (pitch-up) from loss of lift aft of the CG at the tips
- BAn increase in longitudinal static stability
- CNo change in pitching moment, only reduced roll control
- DA nose-down pitching moment from center of pressure moving aft
Show answer & explanationAnswer & explanation
Correct answer: A. A nose-up pitching moment (pitch-up) from loss of lift aft of the CG at the tips
Because swept wings have their tips located aft of the center of gravity, tip stall causes a loss of lift aft of the CG, producing a nose-up pitching moment (pitch-up) that can further increase angle of attack and worsen the stall — a self-aggravating tendency.
Why the other options are wrong
- B. Pitch-up reduces, not increases, longitudinal stability near the stall.
- C. Pitch-up is a well-documented hazard beyond just roll control loss.
- D. Aft CP shift with nose-down pitch describes Mach tuck, a different phenomenon.
Swept-Wing Pitch-Up
A destabilizing nose-up pitching tendency that occurs when wingtips (located aft of the CG on a swept wing) stall before the wing root, reducing lift aft of the CG.
- Caused by spanwise (outboard) airflow encouraging tip stall
- Wingtips are aft of CG on swept wings, so tip stall shifts lift forward, causing nose-up moment
- Counteracted with stall strips, vortex generators, or leading-edge devices
Memory trick: Tips stall first, tail lifts, nose rises — pitch-up peril