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Aviation History
1937
1937 - 0030.PDF
Above : The arrangement of accessories on top and rear covers of the new engine and (right) the latest design of valve gear. (Flight photograph.) absorb the power developed at 2,400 r.p.m. During a further period frequent changes were made in the pitch setting of the airscrew. Further experiments were con ducted with the engine driving, in turn, a wooden airscrew, a Fairey Reed and a two-position variable-pitch airscrew, torsiographs being taken to determine whether it was free from any serious period of torsional vibration. Some quite astounding results were obtained from a supercharged Gipsy Six II, regarded, for the purpose oi experiments, as one half of a "Twelve." It was run for twenty hours at 2,600 r.p.m., the output being 309 h.p. with 4 lb. boost. At even higher r.p.m. and approxi mately the same boost the power was 325 h.p. There appears to be current some confusion about the exact I \md£ FLIGHT. JANUARY 7, 1937. advantages of the new engine over the Series I. Its virtues might be summarised in that it has been planned to operate at a higher continuous power output for level cruising and delivers considerably increased power at a higher crankshaft speed for take-off and climb. This extra efficiency has been obtained at the expense of a very slight increase in weight. It may be recalled that when De Havillands secured from the American Hamilton concern the licence to manu facture their hydraulically controllable airscrews no units had been produced for engines of under about 400 h.p. It was felt that the high cost of the development work which would be entailed to keep the size and weight of the operating mechanism within the desired limits tor an engine of 130-200 h.p. would be more than justified. One of the greatest problems to be faced was that of cooling the engine. It was necessary to make the pitch- changing mechanism particularly compact and to preserve the aerofoil section of the blades as far inward to the hub as possible to ensure satisfactory cooling when climbing and taxi-ing. All requirements were successfully met, and the result was the " 1,000 " size airscrew weighing about 70 lb. and having a pitch range of 9 deg. Development work is proceeding with a new model on similar lines, but having a pitch range of 14 deg. When the first batch of Gipsy Six lis and " 1,000 " size airscrews was tried out in Percival machines in the Schlesinger race (in which the combination functioned flawlessly) spinners were not available, but these accessories (weight 7\ lb.) can now be supplied. The price of the engine with standard equipment is £750. A new version of the Gipsy Major, developed on similar lines to the improved Six, will soon be available. Components and Accessories The following products are included in the Series II engine: Crankshaft steel by English Steel Corporation, Weyburn Every component ot the " 1,000 " type D.H. variable-pitch airscrew is visible below. This screw is suitable for engines between 130 and 200 h.p. (Flight photograph.)
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