Comparison of Nonlinear Aeroelastic Methods for Maneuver Simulation of Very Flexible Aircraft

This paper compares different methods and frameworks for the nonlinear aeroelastic simulation of very flexible aircraft, in particular for the X-HALE UAV configuration from the University of Michigan. The goal of this effort is the in-depth investigation of the influence of different aerodynamic methods with focus on elastic deformations and flight trajectories. Three state-of-the-art programs are applied. The first one is the UM/NAST aeroelastic toolbox from University of Michigan which uses both a corrected 2D strip theory aerodynamic model and, in its latest version, an unsteady vortex lattice solver together with a geometrically exact, strain-based beam formulation. The second one is an aeroelastic solver developed at the DLR Institute of Aeroelasticity. It uses an unsteady vortex lattice aerodynamic method and an extended modal approach for the structural dynamics solution. For selected test cases, the results of Nastran solution sequences SOL144 and SOL146 are used as additional references. The X-HALE UAV is the test case for the numerical studies in this work. Steady polars, unsteady aeroelastic gust responses, and a dynamic maneuver in free-flight with tail input are simulated. Emphasis is put on a systematic analysis of the differences that recent comparisons revealed for this test case. The findings show that the differences can be traced back to the strip theory aerodynamic method. Its drawbacks, in particular the nonconsideration of the aerodynamic interaction of different lifting surfaces, hamper the aeroelastic analysis of complex aircraft configurations such as the X-HALE