Enhanced Modal Approach for Free-flight Nonlinear Aeroelastic Simulation of Very Flexible Aircraft

Abstract

A recently proposed modal-based method that captures the geometric nonlinear effects in the regime of large deformations is applied to the modeling of University of Michigan’s X-HALE UAV. The method is an extension of the classical modal approach towards large geometric deflections and uses higher-order stiffness terms and mode components to ac- count for nonlinear force-displacement relationships and geometrically nonlinear displace- ment fields. In this paper, the method is further extended to enable rigid body motions of an aircraft in free flight. The verification of this extension is done using the X-HALE model which is considered as a challenging test case due to pronounced nonlinearities in steady and unsteady flight conditions. A structural and an aerodynamic model of the X-HALE UAV were built and aeroelastic simulations of the model were done and validated with UM/NAST results.