A FEM-based approach for nonlinear aeroelastic trim of highly flexible aircraft

A novel approach is presented to compute nonlinear aeroelastic trim of highly flexible aircraft by coupling off-the-shelf solvers for structures and aerodynamics. The methodology includes an inertia relief algorithm for large displacements to perform nonlinear static analysis of unrestrained bodies, which is currently not possible in commercially available finite element codes. This feature allows to simulate free-free boundary conditions at each step of the nonlinear aeroelastic trim iterative solution sequence. The proposed approach is implemented by coupling the MSC.Nastran nonlinear structural solver SOL 400 with a three-dimensional vortex lattice method code. Loads and displacements interpolations between aerodynamic and structural grids are performed using MSC.Nastran six degree-of-freedom splines. The computational environment is tested on a beam-type model of the University of Michigan’s X-HALE, a highly flexible experimental unmanned aerial vehicle for nonlinear aeroelastic flight tests. Numerical results are compared with the University of Michigan’s Nonlinear Aeroelastic Simulation Toolbox and with an aeroelastic solver developed at the German Aerospace Center.