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Aviation History
1955
1955 - 1693.PDF
812 FLIGHT, 25 November 1955 DESIGN ASPECTS DISCUSSED... were both required. Because of scatter, life predictions requiredthe testing of several specimens and, since major tests were extremely costly and could not be repeated as a routine, the mainspearhead of the attack on fatigue was through the testing of critical components. The main functions of a major test were toindicate weak places and critical components which would other- wise remain unsuspected, and to enable a study of crack propaga-tion to be made. With the prospect of supersonic speeds at high Mach numbers,structural testing had to combine mechanical loading with a com- plex thermal-loading system. The most difficult problem inreproducing appropriate thermal conditions lay in providing a suitable heat source. There were three main requirements forsuch a source: (1) a high rate of heat generation; (2) an easily and rapidly controlled output; and (3) a controlled variation of heatover different parts of the surface under test. One suitable system was that which employed quartz infra-redlamps, which permitted a heat input to the surface of 20 kW/sq ft. The use of electronic controllers and large numbers of lampsprovided suitable variations of temperature-pattern with time and on the surface, and this method was at present in an advancedstage of development. An important alternative was heating by electro-magnetic induction, which gave an extremely high rateof heat input. Disadvantages of this method were that the heat variation over the surface was less amenable to control, and therate of heat production depended on the electrical and magnetic properties of the structural material. The discussion after Dr. Walker's paper included the follow-ing points. From the stressing point of view, could heat and distributed loading be applied accurately together, or would therebe a return to approximation? Dr. Walker replied that some simplification would be necessary, but, in general, bolder assump-tions and increased complication would be required. Was there any method of detecting cracks inside structures? Not yet, inthe lecturer's opinion. X-ray inspection schedules as provided for inspectors by certain American manufacturers, one speakerpointed out, were most valuable in the search for cracks. After a break for tea the proceedings closed with a generaldiscussion of topics raised during the day. The question of the fail-safe principle appeared first. Dr. Walker said he disliked applying the word "safe" to any type of failure, however limitedin character. The aircraft should be so designed that it would not crack; if there were an error of judgment in this, then fail-safedesign was legitimate as a first reserve. Mr. Oram (Bristol Aero- plane Co.) claimed that the fail-safe principle was a defence indepth which enabled aircraft to continue operating after a crack had appeared. Mr. Walter Tye (A.R.B.) suggested that this struc-tural principle was approaching those which had been applied for many years to engines and equipment: 100 per cent reliabilityhad not been assumed and so precautions had been taken to give non-catastrophic failure. Concerning the properties of modern light alloys, Mr. Peel(High Duty Alloys) suggested that many troubles in the past had been caused by a lack of understanding by the detail designer.Materials had perhaps been blamed for design-office faults, and to move away from modern high-strength alloys would be abackward step. Referring to the effect of dents and scratches occurring toaircraft in airline operation, Mr. Williams suggested that this type of damage should be simulated in all major fatigue tests.Dr. Hislop (Fairey Aviation) disagreed, urging that a practical evaluation of how much damage was done by the operator shouldfirst be made. On the subject of g-restrictors, Dr. Walker denounced theiruse. They had not proved to be safety devices, he said; the initial concept was wrong and had been followed by literally disastrousresults. The development of an autopilot capable of anticipating high values of g well in advance of maximum g would be a betterapproach. Another speaker claimed that too much attention had been paid to solving the practical aspects of the problem andnot enough to tackling the theory. Mr. Giddings said he thought more use could be made of analogues on both static and dynamicproblems. Earlier, another speaker had suggested (in connection with the calculation and measurement of flight loads) that stress-ing was an inaccurate science, and would not provide the solution. We should base flight-load work on an engineering approach, heclaimed, rather than "bury our heads in the sand with a digital computor." Summing up, Sir Arnold Hall suggested that the right pathlay between the two extremes of the practical engineer and the long-haired theorist. It would not be wise, he thought, fordesigners to turn their backs on all modern devices. MOUNTAINEERING AUSTER HIGH-ALTITUDE mountain landings in New Zealand'ssnow-clad "Southern Alps" have recently been made in the ski-equipped Auster shown below, owned and piloted by HarryWigley of South Canterbury. These flights have made possible easy access for skiers to the popular winter-sports region nearMount Cook (12,350ft). Wigley himself is a former champion ski runner, was an R.N.Z.A.F. pilot during the war, and is nowone of the country's most experienced mountain pilots. The use of ski-planes in the New Zealand mountains has the enthusiastic approval of Sir Edmund Hillary, who has alreadyvisited the Mount Cook region in the ski-fitted Auster. Sir Edmund did much of his preliminary mountain training for thesuccessful Everest attempt in this district. Professional photographers, too, have taken advantage of theflights to take heavy equipment to the snow-covered glaciers for mountain photography—the crisp picture below was taken a fewweeks ago by Guy Mannering, a Christchurch photographer who is also an active mountaineer. The ski-equipped Auster J.ld Aiglet, pictured on a snowfield on the Upper Tosman glacier near Mount Cook, New Zealand's highest peak.
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