Nonlinear Gust Response of Highly Flexible Aircraft

Abstract

The paper presents a methodology for calculating the gust response of highly flexible aircraft. Two types of gust analyses are considered, viz. frequency domain and time domain. This work is a continuation of past work 1 in which we presented analysis and results illustrating the linear response of a flying wing configuration to continuous gust based on frequency domain analysis. The linear aeroelastic system was obtained by calculating the trim state of the fully nonlinear aeroelastic/flight mechanics model followed by linearization at the trim state. In the present work, time-domain simulations are used to derive the stochastic gust response estimates. The methodology starts by creating a gust input time series based on the assumed gust power spectral density. The response stochastic parameters can be calculated from the response time series. The calculated time domain response to linearized system matches with frequency domain response calculated earlier. Furthermore, time simulations can be conducted on time marching schemes (e.g., CFD based aeroelastic computations) and can be used to predict the response of the nonlinear system. The aeroelastic model is based on a geometrically-exact, nonlinear beam model coupled with large angle aerodynamic model. The details of the model are shown in Ref. 2 This model has been implemented into a code called NATASHA (Nonlinear Aeroelastic Trim and Stability Analysis for HALE Aircraft). Frequency (linear) and time (linear as well as nonlinear) domain simulations have been added to the formulation and incorporated into the code.