FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
A transport-category airplane in cruise flight encounters a gust that produces a momentary sideslip to the right. As a result, the right (windward) wing develops a higher angle of attack and more lift than the left wing, producing a rolling moment that returns the wings to level without pilot input. This self-correcting tendency is primarily the result of which design feature?
- AAdverse yaw from aileron deflection
- BSpiral instability
- CWing washout
- DPositive wing dihedral
Show answer & explanationAnswer & explanation
Correct answer: D. Positive wing dihedral
Positive dihedral causes the windward (lower) wing in a sideslip to meet the relative wind at a higher effective angle of attack, generating more lift and a restoring rolling moment toward wings-level, which is the classic 'dihedral effect' contributing to lateral stability.
Why the other options are wrong
- A. Adverse yaw is a roll-control side effect from ailerons, not a sideslip-restoring force.
- B. Spiral instability describes a divergent, not restoring, tendency in a bank.
- C. Wing washout reduces tip AoA to control stall progression, unrelated to sideslip response.
Dihedral Effect
The tendency of a wing with positive dihedral to generate a restoring rolling moment toward wings-level flight when the aircraft sideslips.
- Windward wing gets higher effective AoA in a sideslip, producing more lift.
- Positive dihedral is a primary contributor to lateral (roll) stability.
- Excessive dihedral effect can contribute to unwanted dutch roll tendencies.
Memory trick: Dihedral wings tip the scale back to level, like a seesaw righting itself