Aircraft dynamic modes

The Anstellwinkelschwingung, and alpha - vibration (English short period ) referred to in the flight mechanics an oscillation about the transverse axis.

Appearance

The Anstellwinkelschwingung is an oscillatory motion about the transverse axis, with the angle of attack changes, but remain airspeed and attitude angle approximately constant. Depending on the aircraft type and flight speed this vibration occurs at frequencies of a few Hertz. In configurations with separate tail it is very strongly damped and decays before it comes to an oscillatory motion, but it can occur in flying wing aircraft due to the lower attenuation than vibration in appearance.

Calculation

For the calculation of the equations of motion Anstellschwingung be placed and write the coefficients in a matrix. The eigenvalues ​​of the matrix are two complex conjugate pairs of values ​​; they correspond to the frequencies of the eigenmodes of the Anstellwinkelschwingung and the phugoid. The eigenvectors describe the appearance of the mode shape.

Occurrence

The Anstellwinkelschwingung occurs in response to the aircraft elevator inputs in appearance and can result in unfavorable circumstances to flutter. In a highly stretched flying wing with swept- wing, they can be coupled to the bending vibration of the wing, and both times the oscillations at each other when approaching their natural frequencies.

For airplanes with very sensitive level control of the pilot, this oscillation can foment unconsciously when overdriven and attempts to compensate for this control input. If his response delay is close to the half period of Anstellwinkelschwingung, its control signal is always only take place when the aircraft itself returns to the already trimmed angle of attack, and strengthen the vibration. This is one of the pilot induced oscillation (Pilot Induced Oscillation ).