Nonlinear model order reduction for rapid gust loads analysis of flexible manoeuvring aircraft

Abstract

This paper describes a systematic approach to the nonlinear model order reduction of free–flying flexible aircraft and the subsequent flight control system design. System nonlinearities arise due to large wing deformations and the coupling between flexible and rigid–body dynamics. The nonlinear flight dynamics equations are linearised and the approach uses information on the eigenspectrum of the resulting coupled system Jacobian matrix and projects it through a series expansion onto a small basis of eigenvectors representative of the full–order model dynamics. A very flexible aircraft representative of a high–altitude long–endurance (HALE) aircraft is implemented and the aeroelastic solver is verified against results from the literature. Furthermore, a very large flexible wing of high–aspect ratio is built and the flexibility effects on the flight dynamic response are investigated. The reduced–order model eigenvalue basis is identified and convergence studies are performed. Reduced–order models are generated and used for fast parametric worst–case gust searches of the full–order nonlinear flight dynamic response and are exploited in a robust control methodology for load alleviation. Finally, the performance of the controller is investigated on the nonlinear full–order model for various gust lengths