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