D.Y. Maharaj, G. Rosenberg, D.A. Cowling

The effects of backlash (freeplay) on flight control system/structural mode coupling are assessed using a mathematical model of an actuation system with representative backlash in its attachment and output bearings. The analysis is carried out in the time domain using numerical integration so that the nonlinearities can be introduced. The actuation system used for the analysis is a typical fly-by-wire unit for the canard control surface of a fighter aircraft. The model is developed from physical principles and correctly displays the frequency response and impedance characteristics over the required frequency range. The effect of the backlash is greatest at low amplitudes, while at larger amplitudes it becomes less noticeable. The cases studied here, are at low amplitudes typical of those used in FCS/structural coupling tests. The effect of the backlashes is to increase the phase lag while reducing the critical resonance peaks, giving an apparent improvement in FCS/structural coupling gain margins. However, the calculation of closed loop stability from the open loop frequency response does not apply for a nonlinear system, so this may not be a valid conclusion. The study has been confined to zero speed open loop and limited closed loop cases, although the analysis applies equally to inflight cases. Recommended further study is to assess the effect of backlash on closed loop FCS/structural coupling, flutter speed and possible low amplitude limit cycles. These can all be evaluated using a similar model but with aerodynamics included in the aircraft equations.

International Forum on Aeroelasticity and Structural Dynamics 1991, Aachen

Conference Paper

englisch

21,0 x 29,7 cm, 10 Seiten

DGLR-Bericht, 1991, 1991-06, International Forum on Aeroelasticity and Structural Dynamics 1991 Proceedings; S.394-403; 1991; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aeroelasticity

Bestellbar

1991