A pilot inadvertently exceeds the airplane's never-exceed speed (Vne) during a steep descent. Shortly after, the pilot notices a rapidly increasing, uncommanded vibration in the elevator that grows in amplitude within seconds. What aerodynamic phenomenon is most likely occurring, and why does exceeding Vne make it more likely?
- AFlutter — a self-excited oscillation from coupling of aerodynamic, inertial, and elastic forces on a control surface that can become destructively divergent at high speeds
- BMach tuck — a nose-down pitching moment caused by aft movement of the center of pressure near critical Mach number
- CStatic longitudinal instability caused by an aft center of gravity shifting during the descent
- DDutch roll caused by insufficient directional stability relative to dihedral effect at high airspeed
Show answer & explanationAnswer & explanation
Correct answer: A. Flutter — a self-excited oscillation from coupling of aerodynamic, inertial, and elastic forces on a control surface that can become destructively divergent at high speeds
Flutter is a self-excited, potentially divergent oscillation resulting from the interaction of aerodynamic forces, structural elasticity, and inertia in a control surface or airframe component. Its onset speed decreases with reduced structural stiffness or increased mass imbalance, and airspeeds above Vne place the aircraft in a region where aerodynamic forces can overcome damping, allowing flutter amplitude to grow rapidly and potentially cause structural failure — which is precisely why Vne is established to avoid it.
Why the other options are wrong
- B. Mach tuck is a pitching moment tied to compressibility, not a rapidly growing vibration in a control surface.
- C. CG position affects static stability trends but does not create a rapidly growing vibration like this.
- D. Dutch roll is a lateral-directional airframe oscillation, not a rapidly amplifying elevator vibration tied to speed limits.
Flutter
A potentially divergent, self-excited oscillation of a control surface or structure caused by the interaction of aerodynamic, inertial, and elastic forces, most likely at high airspeeds.
- Occurs when aerodynamic forces overcome structural damping
- Can grow rapidly in amplitude and cause structural failure
- Vne is set with margin to avoid the onset of flutter
Memory trick: Flutter is the flag flapping wildly right before it tears — faster air, worse shake.