Pilot-Induced Oscillation Analysis and Prediction with Actuator Rate Limiting

Abstract

Akeyfeatureofall of therecentwell-recordedseverepilot-induced oscillations (PIOs)isthepresenceof actuator rate limiting. As part of attempts to develop a comprehensive understanding of PIO phenomena, the results of an effort focused on improved understanding and analysis of actuator rate limiting are presented. For this effort describing functions were used in concert with modern computer simulation techniques to quantify the added phase lag, magnitude reduction, and bandwidth reduction of a rate-limited actuator in terms of the input and actuator design parameters. The results and inverse describing function techniques are then employed to analyze thelimit cyclepotential of a system that isessentially linearexceptfortheseriesnonlinearity. Thewell-documented X-15 landing e are PIO is used to exemplify these analysis techniques. From this example it is shown that these techniques can be used to provide a prediction of the limit cycle or PIO frequency.