Parametric design studies of GATOR morphing fairings for folding wingtip joints

This paper presents the modelling of a morphing fairing designed to cover the joint on hinged commercial airliner wingtips, such as the semi-aeroelastic Hinge concept. The fairing is made from geometrically anisotropic thermoplastic rubber morphing skin panels, which are 3D-printed multi-material thermoplastic polyurethane sandwich panels combining flexible facesheets with zero Poisson’s ratio cellular cores to provide large extension capability alongside high out-of-plane stiffness. The morphing fairing is designed to cover the gaps in the hinge with a smooth and continuous surface while minimising added torsional stiffness and distortion of the aerofoil cross-section during wingtip rotation. In order to model the mechanical response of this structure at a reasonable computational cost, a homogenisation approach is proposed, wherein the elastic properties of the panel are homogenised to an equivalent shell stiffness matrix through detailed finite element studies on unit cells. These equivalent shell properties are then applied to the three-dimensional geometry of the wing to predict the global response of the fairing during wingtip rotation. This model is then used to parametrically study the effects of varying panel and fairing design parameters on the two design objectives of minimising torsional stiffness and cross-section distortion. The study indicates that cross-section distortion is best minimised by increasing the skin panel’s core thickness, with the other panel design variables having significantly less impact. In contrast, all design variables significantly affect torsional stiffness, with decreasing facesheet thickness and increasing core chevron wall length and chevron angle being particularly effective at reducing torque. The impact of pre-straining the skin panels is also studied, as is the use of additional internal ribs within the fairing, where both approaches reduce distortion at the cost of modestly higher torque. Together, these results clearly indicate the underlying design trends, useful ranges of design variables, and the strong competition between design objectives.