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Aviation History
1927
1927 - 0528.PDF
JULY 14, 1927 THE MARCONI-NEWTON CONSTANT-SPEED WINDMILL A New Electric Power Generator for Aircraft THE recent record-breaking flights of Capt. Lindbergh and Capt. Chamberlin, the gallant, but not quite successful non- stop flight to India, and the tragic attempt of Capt. Nun- gesser, have once more drawn attention to the great strides that are taking place in the development of aeroplanes and in aerial travel. While, possibly, improvements in engines and the size, speed and carrying capacity of aeroplanes attract more public attention and are more generally known, equally important developments in the equipment of the planes which have a vital bearing on the carrying through of successful aerial journeys are not so well known. Second only in importance to reliability of plane structure and engine is the question of navigation, and this may be roughly divided under headings (1) Dead reckoning by the aid of compass only ; (2) dead reckoning by compass checked by a series of solar or stellar observations ; (3) wireless transmission and^direction-fin ding equipment. (2) Some form of voltage regulator more or less automatic ; this has the disadvantage of being liable to give more trouble than the generator, and does not, of course, put any limit on the mechanical stresses resulting from overspeeding. (3) A centrifugal clutch introduced between the windmill and the generator. (4) Some form of automatically variable pitch windmill to rotate at a constant speed over widely-varying wind speeds. The new patent Marconi-Newton windmill, which is shown in the accompanying illustrations, has recently been placed on the market after a prolonged period of experimental and development work, and solves the problem of constant speed by a careful application of scientific principles carried out in a mechanically first-class way. It will be noted that the windmill is extremely compact and consists of a small elliptical hub completely enclosing tin- governor and actuating mechanism, and to which the blades H E H E m H H H H H H E 13 H H a H a m H 13 HHHHHHHI3 The Marconi- Newton Constant- Speed Windmill: This is a new electric power generator for air- craft, shown with its component parts dismantled (top) and com- plete, as mounted to the aircraft (bottom). HHH0HHHH With modern equipment by means of wireless the exactposition of a plane can be determined by the pilot with comparative ease, but anything which simplifies the opera-tion of such equipment by way of making less demands on the energies of the personnel and at the same time conducesto the greater reliability and consistent functioning of the apparatus is of importance. In the case of wireless transmission, plane lighting and thefurnishing of current for electrically-warmed clothing, etc., the source of supply is generally a small specially-constructedlight-weight Streamline contour dynamo generating current at higfl or low voltage, or both, the generator being arrangedin the main air stream or in the slip stream from the main propeller. Originally this had the disadvantage that the revolutionsof the windmill and consequently of the generator varied with the wind speed, resulting in serious fluctuations in the voltageproduced. Various means for overcoming this difficulty have been devised, some being more in the nature of ex-pedients than scientific solutions of the problem. Among various attempts, ranging from what may bedescribed as makeshifts, to devices more or less successful, may be mentioned : (1) The early practice of mounting the generator with itswindmill, so that it could be twisted relative to the air-stream by means of a lever from the cockpit by the operator are mounted on a special form of ball-thrust bearing to reduce friction to a minimum. The blades are exceptionally light and strong, the weight being about 1 J ozs. each and the material, Duralumin tubing, specially annealed and pressed into a true aerofoil section with correct spiral twist by means of forming dies. The tubular end is rivetted to the inner ball race, and in addition, is further secured by means of a shrunk ring. The movement of each blade is governed by a small cylin- drical weight having hardened steel rollers attached.which work in straight guides in an extension of the inner ball race, and in generated spiral guides in the outer ball race, which is securely fixed to the hub. Centrifugal force, due to the rotation of the windmill, causes the weights to move outward against the action of the controlling springs, and the rollers travelling up the guide rotate the blades in relation to the air stream, so that a balance is set up and a constant speed of rotation obtained. The most effective values of spring and weight, and the correct amount of damping have been determined by pro" longed experiments, so that a condition of automatic balana is maintained with complete absence of " hunting " and vibration. The hub is watertight and waterproof, it i* made of sea-resisting aluminium alloy, and is easily attach- able to the generator shaft. The amount of overhang, it should be noted, is extremely small. The overall dimension: 486
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