Novel Tools and Test Techniques for the Evaluation of Aeroservoelastic Free-Play

Control surface free-play is important throughout the lifetime of a flight vehicle. Free-play can result in aeroservoelastic limit cycle oscillations (LCO) with significant amplitude causing degraded mission effectiveness, possibly leading to structural failure. Specifications for allowable free-play size can be overly conservative. Analytical tools are proposed for establishing free-play limits on aeroservoelastic aircraft systems without adverse consequences, justifying relief, which may otherwise be cost prohibitive or impossible to satisfy. The proposed tools include finite element modeling, model order reduction, nonlinear simulation, describing functions, and wavelet transforms. These tools will be integrated into the MatlabTM/SimulinkTM platform. A trade study is proposed that compares different free-play modeling techniques. Novel techniques will be used to determine the airspeed range over which limit cycles can occur, including the frequency and amplitude of the limit cycles. Novel techniques for the inverse problem are also proposed, whereby the free-play size is estimated based on diagnostic measurements. A general stabilator model will be used in Phase I to develop the analysis techniques and show feasibility. Wind tunnel test verification of the free-play analysis and estimation techniques will be conducted in Phase II using existing wind tunnel models and facilities at an industrial location.