Sensitivity of Aeroservoelastic Stability Characteristics Using Parametric Flutter Margins

Abstract

The recently developed parametric flutter margin method is expanded to perform efficient sensitivity studies in which linear and nonlinear flutter characteristics are calculated for changes in selected parameters. Two approaches are suggested: one for structural, aerodynamic, or control parameters that can be formulated as single-input/single-output feedback loops and one for parameters that require multiple-input/multiple-output realization. The single-input/single-output analysis is based on frequency response functions, with the formulation aiming to track the important flutter mechanisms, and is arranged such that the sensitivity to different parameters, over large-variation ranges, may be based on the same set of response functions. The multiple-input/multiple-output analysis is similarly effective but is based on eigensolutions that indicate the parametric changes needed to obtain flutter. Three numerical examples using a generic transport aircraft model, in which sensitivity with respect to stiffness and mass variations were studied, are presented. The single-input/single-output and multiple-input/multiple-output approaches are also applied for calculating damping and frequency variations with velocity that may be used as traditional plots in aeroelastic design and certification tasks. The results demonstrate excellent agreement with those obtained by separate solutions of the MSC/NASTRAN code and nonlinear time marching simulations.