FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightHard
During cruise flight, a pilot momentarily pulls back on the yoke, then releases pressure and lets go. The airplane begins a slow oscillation in pitch attitude and airspeed with a period of about 20 to 30 seconds, with only gradual changes in bank angle and heading, and the oscillations slowly dampen out. This behavior describes:
- Aa phugoid oscillation
- Bshort-period pitch oscillation
- CDutch roll
- Da spiral divergence
Show answer & explanationAnswer & explanation
Correct answer: A. a phugoid oscillation
A phugoid oscillation is a long-period (often 20-60 seconds or more), lightly damped exchange between airspeed and altitude/pitch attitude with nearly constant angle of attack, and minimal effect on bank or heading; this matches the described scenario exactly.
Why the other options are wrong
- B. Short-period oscillations occur rapidly (a few seconds) and are usually heavily damped, unlike the slow 20-30 second period described.
- C. Dutch roll is a coupled yaw-roll oscillation, not primarily a pitch/airspeed oscillation.
- D. Spiral divergence involves a continuously steepening bank and heading change, not primarily pitch/airspeed oscillation.
Phugoid Oscillation
A long-period, lightly damped longitudinal oscillation involving a gradual interchange between airspeed and pitch attitude/altitude, occurring at essentially constant angle of attack.
- Period often ranges from 20 to over 60 seconds
- Angle of attack remains nearly constant throughout
- Minimal effect on bank angle or heading
- Usually only mildly divergent or convergent, easily controlled by the pilot
Memory trick: 'Phugoid = slow float' — long, gentle rise and fall of speed and pitch