FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightMedium
A CFI is explaining an oscillatory motion in which the airplane experiences a combination of yawing and rolling that continues with little damping, most commonly associated with swept-wing airplanes that have strong directional stability relative to their dihedral effect. This motion is known as:
- ASpiral instability
- BAdverse yaw
- CDutch roll
- DPhugoid oscillation
Show answer & explanationAnswer & explanation
Correct answer: C. Dutch roll
Dutch roll is a coupled yaw-roll oscillation that occurs when directional (yaw) stability is strong relative to dihedral (roll) effect, common in swept-wing airplanes. It results in a repeating wing-rocking motion combined with yawing that can persist with little natural damping unless corrected by a yaw damper or pilot input.
Why the other options are wrong
- A. Spiral instability results from the opposite imbalance (weak directional stability) and is a divergent, non-oscillatory spiral.
- B. Adverse yaw is a transient effect of aileron deflection, not a sustained oscillation.
- D. Phugoid is a longitudinal pitch/airspeed oscillation, unrelated to yaw-roll coupling.
Dutch Roll
A coupled yaw-roll oscillation caused by strong directional stability relative to dihedral effect, common in swept-wing aircraft; often corrected with a yaw damper.
- Combination of yawing and rolling motion
- Caused by strong directional stability vs weak dihedral effect
- Common in swept-wing jets; countered by yaw dampers
Memory trick: Dutch roll: the plane 'wags its tail' side to side like a fish