Structure Optimization for Improving Aero-Elastic Cruise Performance of an Aircraft Using the Adjoint Approach

Incorporation of CFRP composite structures into aircraft primary structure enable to design highly flexible wings with a structure response tailored to the requirements. Conventional structure optimization approaches size the aircraft for minimal mass, however the global objective of maximizing aircraft performance is not reflected by this single discipline objective. Starting from a given jig shape, a gradient based optimization of an aircraft wing structure with incorporation of aerodynamic performance is presented in this paper. The performance is evaluated with an aero-elastic aircraft model simulated with DLR TAU and Airbus Lagrange. The novel approach presented here is the calculation of aircraft performance gradients using the coupled aero-structure adjoint. The structure constraints verifying structural integrity, including the gradients thereof are calculated using loads created in Lagrange, coupled to a linear aerodynamic model. Applying a NLPQL optimizer enables to optimize for aircraft performance using the structure design variables as degrees of freedom. The adjoint based gradients are successfully verified to finite difference approximations. The approach is applied on a benchmark testcase with incorporation of CFRP layup optimization. An optimization of a research transport aircraft configuration XRF1 showed the potential of increasing in performance metrics, applying the presented approach, measured by lift over drag