The design of a corrugated skin for the FishBAC compliant structure

The curvature of an airfoil has a significant effect on the generated aerodynamic forces. Researchers have long pursued continuous changes to airfoil camber as an alternative to discrete trailing edge flaps with the potential to significantly reduce drag. The critical components of such morphing structures are mainly the compliant internal structure and an anisotropic skin, both of which have to be stiff to withstand the aerodynamic loads and flexible to enable the morphing deformations. In terms of the internal structure, the investigated design employs a variation of the biologically inspired compliant structure known as the FishBAC to create large continuous changes in airfoil camber and section aerodynamic properties. In terms of the skin, the highly anisotropic behavior of composite corrugated panels is very effective in morphing wing applications where the panels are stiff along the corrugations to withstand the aerodynamic loads and flexible transverse to the corrugations to allow deformation. Recently, the static behaviour of composite corrugated panels has been investigated independently of the internal wing structure through experimental analysis, numerical simulations and analytical equivalent modelling. However, as a proposed candidate for the skin of a morphing wing, the behaviour of these corrugated panels must be investigated comprehensively and optimized in terms of aero-elastic effects and the boundary conditions arising from the internal wing structure. In this paper, the geometric parameters of the coated composite corrugated panels are optimized to minimize the in-plane stiffness and the weight of the skin and to maximize the flexural out-of-plane stiffness of the corrugated skin. The effect of the stringers of the FishBAC as the boundary conditions for the elastomer coated corrugated panel is considered in the optimization process. A finite element code for thin beam elements is used with the aggregate Newton based method to optimize the geometric parameters of the coated corrugated panel.