What is phugoid oscillation?
The phugoid or long period motion is a characteristic oscillations of the aircraft after a small disturbance of the steady flight (ie. due to small horizontal control surface motion or the air gust). The airplane is traveling along the sinusoidal trajectory with small changes of the air speed and pitch angle.
What is short period and long period motion?
The longitudinal motion consists of two distinct oscillations, a long-period oscillation called a phugoid mode and a short-period oscillation referred to as the short-period mode.
How does phugoid change with altitude?
The computations show that Baseline-II E-2 undamped natural frequency of phugoid mode is inversely-proportional to airspeed and reduces as altitude increases. These have adverse effect on its damping ratio that increases near parabolically when the aircraft flies faster, and reduces when it climbs up.
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 aileron reversal?
A situation occurs at some high speed when the moment is so large that there is total loss of lift when the aileron is deflected downward, and the aircraft rolls in the reverse direction. This is called aileron reversal. An adverse effect when an aircraft rolls in the reverse direction of the aileron input.
What is VN diagram?
A chart of speed versus load factor (or V-n diagram) is a way of showing the limits of an aircraft’s performance. It shows how much load factor can be safely achieved at different airspeeds.
What are the factors affecting period and damping of oscillations?
Most noteworthy, the period of oscillation is directly proportional to the arms’ length. Moreover, the period of oscillation is inversely proportional to gravity. An increase in the pendulum arm’s length causes a subsequent increase in the period. Also, a decrease in length causes a decrease in the period.
What is Weathervaning aviation?
Weathervaning or weathercocking is a phenomenon experienced by aircraft on the ground and rotorcraft on the ground and when hovering. As most of the side area of an aircraft will typically be behind this pivoting point, any crosswind will create a yawing moment tending to turn the nose of the aircraft into the wind.
What causes pilot induced oscillation?
Pilot Induced Oscillations are sustained or uncontrollable oscillations resulting from efforts of the pilot to control the aircraft and occur when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions; each one is an attempt to control the aircraft’s reaction …
How do you increase Phugoid damping?
The phugoid has a nearly constant angle of attack but varying pitch, caused by a repeated exchange of airspeed and altitude. It can be excited by an elevator singlet (a short, sharp deflection followed by a return to the centered position) resulting in a pitch increase with no change in trim from the cruise condition.
How do you find time in half amplitude?
- Period: P = 2π
- ηc. ¯c.
- V. Time to half amplitude: T1/2 =
- ln (1/2. )
- ξc. ¯c.
- V. Damping factor: ζ =
- −ξc. |λc|
- Undamped natural frequency: ω0 = |λc| V.
How are short and phugoid period oscillations different?
The short and phugoid period oscillations modes are sieved from the longitudinal dynamic equation and carry the same eigenvalues of the longitudinal model, but they still differ. Firstly, the three systems have different step response trajectories due to their different DC gain values.
Is the short period of oscillation a problem?
The bottom diagram of a short period in Figure 12.12 plots the variation of the angle of attack, a, with time. All aircraft have a short-period mode and it is not problematic for pilots. A well-designed aircraft oscillatory motion is almost unnoticeable because it damps out in about one cycle.
What causes the phugoid motion in an airplane?
Phugoid motion is the slow oscillatory aircraft motion in the pitch plane, as shown in the bottom diagram in Figure 12.12. 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.
Which is the correct description of the phugoid mode?
Thus the phugoid is classical damped harmonic motion resulting in the aircraft flying a gentle sinusoidal flight path about the nominal trimmed height datum. As large inertia and momentum effects are involved, the motion is necessarily relatively slow such that the angular accelerations, ˙q and ˙α(˙w), are insignificantly small.
