Nonlinear Aeroelastic Behavior of Tail / Rudder Systems with Freeplay and Actuator Failure

Abstract

This thesis discusses the development of numerical simulations implemented in MATLAB and of an experimental tail/rudder model for the investigation of the effects of non-linearities on control surface flutter of a three-degree of freedom typical section airfoil. Non-linearities investigated include a structural non-linearity in the form of freeplay about the control surface hinge line as well as velocity-squared damping, simulating a failed actuator. The mathematical modeling, design, and testing of a prototype velocity-squared damper is also presented for use in the numerical simulations. In both cases, the describing function method has been used to predict the amplitudes of possible Limit-Cycle Oscillations (LCOs) in the rudder DOF. Response amplitudes and frequencies in the frequency domain, are shown to agree extremely well with results obtained in the time-domain via direct numerical integration of the equations of motion. Both stable and unstable limit-cycle behavior has been predicted, resulting in a detailed set of predictions for the response of the system below the flutter boundary.