phugoid motion

Phugoid motion is a type of long-period oscillatory motion observed in aircraft flight altitude motion

Phugoid motion is a type of longitudinal oscillatory motion seen in fixed-wing aircraft, where there is a continuous exchange between the aircraft’s kinetic and potential energy. When an aircraft is disturbed from steady-level flight—for example, by a slight pitch-up—it gains altitude while simultaneously losing speed, resulting in a gradual climb followed by a descent as gravity causes it to speed up again. This slow, sinusoidal oscillation in altitude and velocity occurs without significant changes in angle of attack or pitch attitude. The motion has a long period, typically lasting several tens of seconds, and is governed by the aircraft’s aerodynamic and inertial properties. In a statically and dynamically stable aircraft, phugoid oscillations are naturally damped over time, returning the aircraft to steady flight. Understanding phugoid motion is important in aircraft design and control, as it affects flight stability, pilot workload, and automatic flight control system behavior.