phugoid oscillation

To damp the phugoid oscillation naturally, the planes are designed with high drag which reduces flight performance and flying time.

Lack of elevator control is sometimes problematic if the phugoid oscillation isn't well-damped leading to unmanageable "porpoising".

Proportional (vs. "on-off") throttle control which is critical for preventing the excitation of phugoid oscillation ("porpoising") whenever a throttle change is made.

The seed moves through the air like a butterfly in flight - it gains height, stalls, dips and accelerates, once again producing lift, a process termed phugoid oscillation.

The 2003 crash of the Helios solar powered aircraft was precipitated by reacting to an inappropriately diagnosed phugoid oscillation which ultimately resulted in the aircraft structure exceeding design loads.

The phugoid oscillation is really a slow interchange of kinetic energy (velocity) and potential energy (height) about some equilibrium energy level as the aircraft attempts to re-establish the equilibrium level-flight condition from which it had been disturbed.

In the 1975 Tan Son Nhut C-5 accident, USAF C-5 68-0218 with flight controls damaged by failure of the rear cargo/pressure door, encountered phugoid oscillations while the crew was attempting a return to base, and crash-landed in a rice paddy adjacent to the airport.

The longitudinal modes of a statically stable airplane following a disturbance were shown to consist of a long-period oscillation called the phugoid oscillation, usually with a period in seconds about one-quarter of the airspeed in miles per hour and a short-period oscillation with a period of only a few seconds.

After State acceptance trials production was not recommended due to poor spinning characteristics, directional stability and control issues, nosewheel shimmy, poor controllability when landing in crosswinds above 6 m/s (12 kt) and, last but not least, phugoid oscillations in all-three axes which were difficult to control and made piloting the prototype very tiring.