Parametric Flutter Margin Method for Aeroservoelastic Stability Analysis

Abstract

A new parametric flutter margin method for linear and nonlinear stability analysis of aeroservoelastic systems is presented. The method is based on frequency-response calculations with the system stabilized using a single selected structural, aerodynamic, or control parameter, which facilitates convenient response calculations with smooth response variations with respect to the excitation frequency and flight conditions. The frequency-response functions are used for generating flutter margins with respect to the added parameter. The linear flutter or nonlinear limit-cycle oscillation characteristics are those at which the margins become zero. Furthermore, the method facilitates convenient and efficient design studies with respect to linear and nonlinear variations of the selected parameter. A frequency-domain response analysis is first performed with the linear part of the model. Increased-order modeling concepts may then be applied to add nonlinear effects using time-domain convolution or harmonic-balance methods. Three numerical applications are given, one with a classic wing section with flap and two with a generic transport aircraft model. The examples include bending-torsion and control-surface flutter cases, with and without control-system and actuator free-play effects. The results demonstrate excellent agreement with those obtained using traditional flutter methods and nonlinear time-marching simulations.