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SEVERAL years before the British and French Governments decided, separately, to initiate feasibility studies into the building of a supersonic transport passenger‐carrying aircraft with an auminium alloy as the main structural material, the Research and Development Division of High Duty Alloys Ltd. began to compare the relative merits of selected Hiduminium alloys in anticipation of this possible new application. It was appreciated that the life requirement, for ecenomic reasons, would be between 20,000 and 30,000 hours and that the saturation skin temperature, due to kinetic heating, at speeds of Mach 2·2 and 2·5 would be about 120° and 150°C, respectively. The Division's considerable experience in the field of developing aluminium alloys for acro‐gas turbine applications for service at temperatures higher than this range, made us optimistic about the possibility of being able to develop a wrought aluminium alloy which would meet all the mechanical property requirements for the construction of a SST aircraft.

There is a scarcity of specific design data which can be presented to the aircraft designer to enable him to assess the most suitable structural aluminium alloy for a high speed civilian transport aircraft. The problem is essentially due to the relatively low range of elevated temperatures, in which he is interested, coupled with the very long life requirements for a commercial transport aircraft flying at speeds at which it is possible to consider the use of aluminium alloys.Although the firm with which the author is associated has a vast experience in the development and knowledge of aluminium alloys for aero-engine and gas turbine purposes, it has never been required, in the past, to consider engine applications much below about 200°C, and the design data, which was determined over many years and provided as a service, satisfied the engine designers if the period of test was up to 1,000 hours. On the other hand, to the designer of aircraft for subsonic flight, kinetic heating is no problem at all, and he is quite satisfied with a knowledge of the room temperature properties of the various alloys.

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