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What is time to half amplitude?
The time when the amplitude decreases to half of its value at t = 0, is a measure of the damping. This time is denoted by t1/2.
What is meant by phugoid?
: of, relating to, or representing variations in the longitudinal motion or course of the center of mass of an airplane in flight.
Which are the aircraft oscillatory modes?
If damping is too low, turbulence or control inputs can excite the aircraft too readily; its behavior appears skittish. There are two modes of pitch oscillation: the heavily damped short period mode (damping ratio about 0.3 or greater), followed by the lightly damped, and more familiar, long period, phugoid mode.
What is Phugoid oscillation?
Phugoid (longer period) oscillations The phugoid oscillation is 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.
What is meant by Phugoid oscillation?
A phugoid or fugoid /ˈfjuːɡɔɪd/ is an aircraft motion in which the vehicle pitches up and climbs, and then pitches down and descends, accompanied by speeding up and slowing down as it goes “downhill” and “uphill”.
How is the frequency of a phugoid oscillation related to speed?
The frequency of a phugoid oscillation is inversely proportional to an aircraft’s speed. Its damping also is inversely proportional to the aircraft L/D ratio. A high L/D ratio is a measure of aircraft performance efficiency.
How long does it take for a phugoid to settle?
Phugoid is a hands-off (i.e. pilot and autopilot off) rigid-body mode, with or without Stability Augmentation System. MIL-STD-1797B specifies a damping ratio of at least 0.04 for Level 1 handling quality. The typical phugoid period is around 90 seconds. This converts to a settling time (within 2% of trim speed) of around 24 minutes.
When to excite phugoid mode with longitudinal control?
From the trimmed position, excite the phugoid mode by applying longitudinal control in one direction in order to change airspeed by approximately 10 kts, then release. To answer the additional question of when the resulting motion amplitude would be below 0.1 deg, I made a kind of a digital simulation according to this block diagram:
How long does a long period oscillation last?
It is known as the long-period oscillation (LPO) – the period can last from 30 s to more than 1 min. Typically, a pilot causes the LPO by a slow up and down movement of the elevator. In this case, the angle of attack, a, remains almost unchanged while in the oscillatory motion.