Design and optimisation of a highly flexible wing structure for a generic long-range aircraft

Kurzfassung

Due to the increased application of carbon fibre reinforced plastics (CFRP) in the aircraft industry in the past decades, design of primary load carrying structures has vastly evolved. Particularly, the Airbus A350 and the Boeing 787 are well known for their complete integral structures fabricated entirely out of CFRP. Ultimately, this led to weight saving and a wider design space as the result of reduced material density and the anisotropic nature of the composite. However, the aforementioned design space is currently limited by uncertainties such as material imperfections, open hole tensions or plate boarder stresses. These uncertainties are commonly overcome by applying large safety margins, limiting the benefit of replacing aluminium with carbon fibre. This work analyses the impact of increased strain failure limits on the structural optimisation of an aircraft wing structure. The goal is the design of a highly flexible wing box to form the groundwork for further research on the effects of large, geometrically nonlinear deformations in the field of aeroelasticity. Therefore, a parametric, in-house model generator is used to build a research model which features the attributes of a modern long range jet transport. Throughout this paper, simulation model components and topological decisions are presented, as well as the loads and optimisation tool chain which is applied to dimension the structure. The optimisation of the composite skin is based on a lamination parameter methodology in which the shell elements are restricted by strain and intracell buckling constraints. Initial results obtained from geometrically nonlinear finite element calculations with varying static manoeuvre loads indicate that the optimised structure is suffering from buckling of whole stiffened panels. As a consequence, responses obtained by linear buckling analyses are considered in the optimisation as well. Finally, the results of a parameter variation are presented. The generated structural model features a vertical wing tip displacement of 8.6% with respect to the wing half span during design cruise flight. Furthermore, the usability of the optimisation results for geometrically nonlinear calculations is demonstrated.