Design and Manufacturing of Composite Aerospace Load Introduction Structures

Abstract

This paper focuses on the design philosophy of innovative composite load introduction structures for aircraft high-lift devices. In a joint project between different EADS Business Units, design principles for new composite flap support system are developed. The load introduction of these composite high-lift elements is investigated in detail. The design of single pin load introduction can be divided into composite lugs and load introduction loops. Both designs are numerically analyzed with finite elements using non-linear boundary conditions (e.g. gap elements, deformable body contact definitions) and are afterwards verified by static tests. It is shown that force introduction loops have advantages at in-plane tensile loads, but lead to poor performance at out of plane loads in comparison to composite lugs. Thus load introduction loops can be used for applications with limited design space and in-plane tensile loads. For multiple loads in various directions composite lugs should be used instead. The investigations further show that friction within the bearing leads to a major load increase. Therefore an comprehensive numerical investigation was conducted to analyse the actual friction moments in bearings dependent on the rotation axis, clamping by the surrounding structure and possible gaps within the bearings. It could be shown, that the real critical friction moments are up to 40% lower, than with a conservative approach. Hence lighter load introduction structures can be designed by taking the precise bearing frictions into account.