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Aviation History
1954
1954 - 0394.PDF
186 FLIGHT HEAT PROBLEMS IN AIRCRAFT STRUCTURES . . . basic theoretical and practical work which they reported was, however, applicable in other fields. They indicated how a step-by- step technique could be used to derive the temperature distribu tion throughout a plate when the boundary temperatures were known, and confirmed that they had successfully used Bakelite gauges for the measurement of steady stresses at temperatures up to 130 deg C. This paper concluded the third session of the conference. The fourth and final session was opened by MR. G. MEIKLE, Metal lurgy Department, R.A.E., who discussed the effects of tempera ture on a number of materials used in aircraft construction. The materials which he considered were D.T.D. 364, D.T.D. 683, L 42, En 24, En 25, En 26, En 110 and S 11. Although these were not primarily designed for use at high temperature, the advent of supersonic aircraft and missiles might cause these materials to be used in structures subjected to kinetic heating. A knowledge of their properties was therefore desirable. The duralumin type alloys (e.g., D.T.D. 364), he demonstrated, had a strength loss at elevated temperature which was independent of time as long as the temperature was not greater than 150 deg C. Between 150 deg C and 300 deg C, however, strength rapidly altered and time had a pronounced effect. At 200 deg C, one hour's heating caused a strength loss of 28 per cent, but 1,000 hours' heating caused a loss of 70 per cent. Once the temperature exceeded 300 deg C approximately, he said, the bad effect on material properties was so great that time had very little influence. The high-strength zinc alloys, as represented by D.T.D. 683 (5 per cent Zn), showed very similar properties, Mr. Meikle said, but in this case the rapid strength fall took place at about 120 deg C. On the other hand, for temperature tests up to 350 deg C, the results which were available on alloy steels indi cated that length of time at temperature had no appreciable effect. This difference in properties was due to the fact that the precipitation which occurred in the aluminium alloys was not experienced in steel to any appreciable extent. Mr. Meikle was followed by MR. D. A. DREW, Vibrations Department, Rolls-Royce, Ltd., who gave the group a review of high-temperature strain gauges. He explained how a gauge capable of operating, say, at 150 deg only could be used for applications which required a higher-temperature unit. This had been accom plished by connecting the gauge to a tube, through which cooling fluid was circulated, and then attaching the tube to the specimen almost in the same way as a normal extensometer. Woven-type gauges, Mr. Drew said, were still in their infancy but the glass weave was most useful as a device for holding the wire in place while the gauge was being attached by means of a suitable ceramic such as Quigley Blue. It was considerably more difficult, he said, to obtain accurate values of steady stresses than of vibratory ones. Subsequent to the lecture it was remarked from the floor that Quigley Blue cement made glass very brittle and Mr. Drew agreed this was the case. This embrittlement, he said, was a drawback at the point at which the glass-covered leads left the gauge, although it was not significant as regards the glass fibres in the gauge itself. The final paper of the conference was presented by MR. B. J. TERRELL, of the Pametrada Research Station, WaUsend. He emphasized the great importance of confirming calculation by practical measurement. He demonstrated with slides a number of interesting techniques which had been used in research measure ments made on steam and gas turbine machinery. The committee of the Stress Analysis Group, and in particular the organizing secretary, Mr. V. M. Hickson, are to be congratu lated on the success of this conference. The papers presented combined a high technical standard with interesting presentation. VULCAN RIDES THE TRAILS This fine new air-to-air impression of the Olympus-Vulcan was taken at the modest altitude of 12,000ft by Avro photographer Paul Cullerne, flying in a Lincoln. The V-bomber was being flown by test pilot Roly Falk. This aircraft and its Sapphire-powered counterpart are now engaged on intensive test-flying concerned with the development of their military equipment.
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