Improving the design of the Eurofighter aircraft airbrake by creating a hybrid assembly of 3D printed brackets and composite structures

Kurzfassung

A lot of composite aircraft structures today are designed according to guidelines that were developed for parts and assemblies made from metal. This is true for the shape of the components as well as for the applied joining concepts. In case of the Eurofighter aircraft airbrake for example this leads to an assembly that consists of about 50 individual components and of about 850 fasteners. A more composite oriented design approach in which functionalities are combined in larger shell shaped components allows us to reduce the number of parts significantly. Furthermore joining the composite components by adhesive bonding saves up to 85% of the fasteners. The main challenge resulting from those two measures is the compensation of geometrical deviations in order to ensure the quality of the aerodynamic shape and to introduce the loads properly. Since an adhesive gap can be used to adjust tolerances only to a very small extend a novel approach has to be investigated. Custom fit load introduction brackets for each individual interface area made by additive layer manufacturing may be able to compensate the deviations of the composite parts. Based on a topology optimization and a 3D geometry measurement of the interface areas of the composite sub-assembly novel load introduction brackets are designed. Selective laser melting of stainless steel and investment casting of aluminium in a mould derived from a 3D printed polymer pattern are chosen to manufacture those brackets. A 3D geometry measurement of the cast aluminium brackets shows that the accuracy is sufficient to compensate the deviations of the composite parts. The deviations of the brackets made from steel by selective laser melting are equal to the deviations of the composite parts and therefore this process is not accurate enough yet. A further assessment of the used ALM processes shows that due to ongoing improvement of the material properties and dropping costs custom fit load introduction brackets can support the composite oriented design of geometrical complex structures.