The design,construction and test of a postbuckled, carbon fibre reinforced plastic wing box

Abstract

A postbuckled, carbon fibre reinforced plastic (CFRP) wing box has been designed, manufactured and tested for an aerobatic light aircraft, the Cranfield Al. Methods of analysis have been evaluated including: i) Non-linear finite element analysis for the prediction o-f panel postbuckling. ii) A simpler technique based on an effective width method. This forms the core of a design program, 'oPTIMIST'. It predicts buckling loads, postbuckled reduced stiffness and overall column failure of co-cured hat stiffened panels. It then optimises the con-Figuration of a box beam for minimum weight. iii) The use of the effective width method allied to a large scale, linear finite element analysis. The work includes the development of a new method o-F construction for composite box structures. The wing skin sti-Ffeners and rib flanges are co-cured together. Integral slotted Joint features are formed in each part. The structure is then adhesively bonded together. A full description of the manufacture o-F the wing box is included. The structure was also tested in a specially designed rig. It was tested to ultimate design loads in: i) Positive bending to 13.33. ii) Negative bending to -96. iii) Pure torsion resulting from full aileron load. iv) Torsion with 96 bending. The compression panels were seen to postbuckle and recover in each load case. Results are compared with theory, and with the original aluminium Al wing. The structure is 257. lighter than its aluminium counterpart. Finally, suggestions are made for possible areas of further research.