Materials for airframes

Abstract

The prediction of the future is always a relatively uncertain process. The only certain fact is that the prediction is unlikely to be wholly accurate. Even the prediction of trends following examination of past performance will be uncertain regarding the future rate of advance and may be entirely upset by new discoveries and their application. This is as true for examining the future of airframe materials as it is for prediction of economic growth, which itself significantly affects the development of materials technology in the aircraft industry. However, 100 years of powered manned flight does give a solid database from which to begin. In that period airframes have moved from wood, wire and canvas, through to riveted and stressed skin metal structures to adhesively bonded polymer composites. In each case the use of new materials is associated with a change in fabrication methods and it may be confidently anticipated that this will remain true in the future. This fact accounts for a justified conservatism in embracing new materials, not simply because of the need to develop experience and confidence in them, but also because of the costs associated with new constructional methods entailed in their application. It also, in part, accounts for the generally slower pace of application of new materials relative to what is initially predicted: the other powerful brake being the state of the economy and the market for new aircraft at any particular time. The early prediction of the demise of aluminium and its replacement by polymer composites made in the 1980s being a case in point, while the failure of alloys containing lithium to replace conventional aluminium alloys had more to do with cost and decreasing fuel prices than any alloy development problems. It can, however, be expected that, as in the twentieth century, military aircraft will exploit larger mass fractions of advanced materials and at earlier dates than civil transport aircraft, given their very different operational requirements and much shorter design lives. The likely advent of unmanned combat aircraft may well accentuate this difference.