FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
During cruise in a swept-wing transport with the yaw damper inoperative, a pilot notices a persistent, lightly damped combined rolling and yawing oscillation. What aerodynamic characteristic is most directly responsible for this motion?
- AExcessive longitudinal static stability
- BInteraction between dihedral effect and directional (weathervane) stability, known as Dutch roll
- CMach tuck caused by aft shift of center of pressure
- DAdverse yaw from aileron deflection alone
Show answer & explanationAnswer & explanation
Correct answer: B. Interaction between dihedral effect and directional (weathervane) stability, known as Dutch roll
Dutch roll results from the interplay between strong dihedral effect (roll due to sideslip, enhanced by wing sweep) and weaker directional stability, producing a coupled yaw-roll oscillation that yaw dampers are specifically installed to suppress.
Why the other options are wrong
- A. Longitudinal static stability concerns pitch, not roll-yaw coupling.
- C. Mach tuck is a pitch phenomenon related to transonic shift of center of pressure.
- D. Adverse yaw is a control-input effect, not a persistent oscillation from stability characteristics.
Dutch Roll
A lateral-directional oscillation combining rolling and yawing motion, caused by strong dihedral effect relative to directional stability, common in swept-wing aircraft.
- Aggravated by wing sweep, which increases effective dihedral
- Yaw dampers are installed to damp the oscillation
- Can occur with yaw damper inoperative during turbulence or crosswind upsets
Memory trick: Dutch roll: the wings waltz side to side