Aeroelastic Sensitivity Analyses for Flutter Speed and Gust Response

Abstract

Two methods for the aeroelastic eigensensitivity analysis and the sensitivity analysis of an aeroelastic discrete-gust response have been developed. Finite state modeling of the unsteady aerodynamics allows one to determine explicitly the aeroelastic sensitivity with respect to a structural design variable and the aeroelastic behavior with respect to other design variables such as fuel weight, wing stiffness, and engine location. An analytical method based on the matched filter theory has been developed that allows one to estimate the sensitivity, with respect to the same design variable, of the maximum peak reached by the gust response due to a discrete gust. This approach allows one to evaluate the maximum value of the response corresponding to a discrete-gust input once the energy level of the input has been established. The sensitivity of this maximum value with respect to an aeroelastic-design variable can be evaluated too. The structural and aerodynamic contributions to the sensitivity have been separately identified following several levels of approximation. Numerical results, in the case of an ultrahigh capacity aircraft wing, are presented. Because of the large flexibility of the wing, the aeroelastic behavior has been included in the stability margin estimate and in the gust response. The application limits of the sensitivity approximations are discussed. The proposed approach, which uses structural and aerodynamic data by standard codes, could be useful in the preliminary design to evaluate and preestimate the aeroelastic performances.