Limit Cycle Prediction For Subsonic Aeroelastic Systems Using Nonlinear System Identification

The prediction of aeroelastic instabilities caused by nonlinear unsteady aerodynamic forces
acting on aircraft has recently become an important area of research. Emphasis is placed on
the capability to predict the occurrence of Limit Cycle Oscillations (LCOs) at both the design
and prototype testing stages. In this paper, the prediction of LCOs is attempted for a simulated
aeroelastic system subjected to nonlinear subsonic unsteady aerodynamic forces, using system
identification. Response data from the simulated system are curve-fitted by means of a series
of polynomial basis functions. This approach yields very accurate identified models of the
actual system at individual flight conditions. These identified models are extrapolated to a
global aeroelastic identified model. Using this model, the flight conditions at which LCOs
occur is accurately predicted but the amplitude of the oscillations is underestimated.