During cruise, a pilot briefly deflects the control yoke forward and releases it. The airplane responds with a rapid, small-amplitude pitching oscillation that damps out within a few seconds, with essentially no noticeable change in airspeed during the event. This response is characteristic of which dynamic mode, and what distinguishes it from a phugoid?
- AShort period oscillation, which involves rapid changes in angle of attack at essentially constant airspeed, occurring over a short period and normally damping quickly
- BSpiral instability, a slow, non-oscillatory divergence in bank angle and heading
- CDutch roll, a combined yawing and rolling oscillation caused by an imbalance between dihedral and directional stability
- DPhugoid oscillation, which involves large airspeed changes at a nearly constant angle of attack over a long period
Show answer & explanationAnswer & explanation
Correct answer: A. Short period oscillation, which involves rapid changes in angle of attack at essentially constant airspeed, occurring over a short period and normally damping quickly
The short period oscillation is a rapid pitching motion involving changes in angle of attack with essentially constant airspeed, typically well-damped and completing within a few seconds. It contrasts with the phugoid, a slow, long-period oscillation involving trade-offs between airspeed and altitude at nearly constant angle of attack.
Why the other options are wrong
- B. Spiral instability is a non-oscillatory divergence, not an oscillation at all.
- C. Dutch roll is a lateral-directional oscillation, not a pitch phenomenon.
- D. This describes the phugoid, the opposite of the rapid, constant-airspeed motion described.
Short Period Oscillation
A rapid, usually well-damped longitudinal oscillation involving changes in angle of attack at essentially constant airspeed, occurring shortly after a pitch disturbance.
- High frequency, short duration (seconds)
- AOA changes while airspeed stays nearly constant
- Contrasts with phugoid: phugoid is slow, long-period, airspeed/altitude trade at ~constant AOA
Memory trick: Short period = quick jolt and settle; phugoid = slow, lazy rollercoaster.