phugoid


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phugoid

[′fü‚gȯid]
(aerospace engineering)
Pertaining to variations in the longitudinal motion or course of the center of mass of an aircraft.

phugoid

phugoidclick for a larger image
A pitching motion in which kinetic and potential energy (speed and altitude, in this case) are traded. Each cycle typically lasts about 60 s and may continue for many minutes. The motion resembles a roller coaster in which, as the aircraft nose pitches up, the air speed decreases, and as the nose drops, the air speed increases. There is, however, little or no change in the load factor if the aircraft has a neutral pitch stability. The pitching motion is usually damped, and the degree of damping is dependent upon the aircraft's design characteristics (i.e., the amount of positive pitch stability).
References in periodicals archive ?
Most have some degree of long-term phugoid, plus they will simply wander after a half-dozen seconds no matter how well trimmed.
On this basis, the proportional-integral-derivative (PID) controller is used to achieve the desired flight performance under the assumption that the short-period dynamics are faster than the phugoid mode [1].
On the other hand, parameters of the phugoid mode change slowly enough for the pilot to modify the oscillation of the aircraft.
A phugoid, while fun to say, is a large scale oscillation characterized by constant AOA but changing pitch and airspeed.
In reality, the resulting motion is a superposition of two fundamental and independent oscillations: the phugoid (or long-period) oscillation and the short-period oscillation.
The T-50's triple-redundant, fly-by-wire control system feeds back a term of one minus the cosine of the pitch angle, essentially eliminating the natural long-period, longitudinal oscillation (known to engineers as the phugoid) that is shared by all stable aircraft.
In slow flight, the Astore has a predictable phugoid recovery when displaced from a trimmed airspeed, but we found this less so at higher speeds, where it was sluggish to recover from a hands-off pitch-down displacement.
The turns onto the localizer from the arc always looked like a shepherd's crook (the overshoot) followed by a decreasing phugoid as you captured the beam.
In trimmed cruise, disturbing the pitch provokes a phugoid that damps almost completely in two cycles, suggesting that the airplane will be a standout for instrument training and instrument flight.
Most have some degree of long-term phugoid, plus they will simply wander after a half dozen seconds no matter how well trimmed.
An excited phugoid seemed to damp back to the trimmed airspeed in less than a cycle, but given the turbulence, we couldn't judge it accurately.