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Aviation History
1947
1947 - 1886.PDF
FLIGHT ROTOR HEAD BRISTOL HELICOPTER . . . COLLECTIVE PITCH CONTROL LEVER LOWER TRANSMISSH GEAR CASE hub-serrated to a coaxial sleeve surrounding the crankshaft extension, this sleeve running back to a bevel pinion which meshes with a bell-type bevel crown-wheel. The crown bevel is hub-serrated to a vertical drive shaft around which are pivoted the toggle-action wedging-levers carrying the slippers which form the freewheel device. Drive is transmitted through the toggle-levers and slippers to an enclosing bell sleeve which, running in a large diameter ball-type steady bearing in the gearbox head, is externally serrated to mesh both with the driving member of the rotor brake and the driving member of an 8-point Layrub flexible coupling. The driven member of the latter is actually the base of the main transmission shaft. The crown part of the gearbox cover carries the rotor-brake shoe-anchorages, the brake itself being a normal car-type expanding unit with twin cam-spread shoes. The main transmission shaft is a 2% in. diameter, 8-gauge steel tube, terminating at the head with another 8-point Layrub coupling to give drive direct to the spur pinion of the upper reduction gear. The base of the enclosing gearbox is bolted, together with the rotor support cone, direct to the boss.of the mounting pylon. In the upper section of the gearbox is .carried a roller bearing in which the inner casing shell rotates, this being bolted to the main spur wheel. On the underside of the spur wheel is bolted a low-angle bevel-annulus which meshes with a bevel pinion for transmitting drive to the tail rotor shaft. The inner shell casing is axially bolted to the base of the rotor hub-forging in which the blades are pivoted. All rotor loads are transmitted down to the pylon and thus to the airframe by means of the rotor support cone, the only loads carried by the gearbox casing being tooth reactions.
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