Patent GB-519562-A (GB)
Title: Improvements relating to fluid-transmission circuits in variablepitch-airscrews
IPC: B64C11/42
Filed: 1939-03-08
Abstract: 519,562. Fluid transmission circuits in variable pitch airscrews. BRISTOL AEROPLANE CO., Ltd., and FEDDEN, A. H. R. March 8, 1939, No. 25473. Divided out of 514,438. [Class 114] A variable pitch airscrew mechanism comprises a hollow shaft enclosing a tube, a bush being interspersed to form two chambers communicating outside and inside respectively and passages being provided to lead through the bush to the chambers from ports in the shaft. One construction is shown in Fig. 1 in which an airscrew hub 10 is splined to a shaft 11 driven at reduced speed from a crankshaft by gearing 15, 16, 18. A hydraulic cylinder 19 has reduced parts 20, 22 respectively sliding in sleeve parts 21 and in a forward part of the shaft 11. A piston 23 carried by a tube 25 is secured to a tail shaft 27 received in crankshaft but separated by a bush 28. An outer tube 29 surrounds the tube 25. Oil under pressure entering the tube 25 passes to the front part of the cylinder 19 to move it forwardly for corresponding pitch adjustments. Oil is discharged from rear chamber through ports 34 into an intertube space 35. Pressure oil entering this space moves cylinder rearwardly, the oil from the front chamber discharging along the tube 25. A booster pump delivers oil at two different pressures, both exceeding lubricating pressure, to the tube 25 and space 35 respectively. Low pressure oil supply and leakage may be allowed for. Modifications are described for different types of airscrew and in Fig. 2 is shown a detailed construction of one form of the invention. Around the shaft 11 is arranged a bush 36 with internal grooves 37, 38 communicating with conduits 39, 40 in the shaft and grooves 41, 42 connected to the booster pump. Oil may be supplied at one pressure to the groove 41 for pitch adjustment in one direction and at another pressure to the groove 42 for reverse direction. A bush 44 is formed peripherally with three goooves 45 separated by corresponding lands and is also formed by terminal flanges 51, 52. The bush is formed with an extension 53 splined to a tube 29 which overlaps an unsplined' part to make a fluid-tight joint. The tail shaft 27 engages the rear end of shaft 11 by centre part 26. Oil under pressure enters the groove 42 and passes by groove 38 and conduit 40 into groove 46 and thence into a chamber 59 and space 62. The oil thereupon passes into the interior of the tube 25 to the front end of the cylinder 19. Oil is correspondingly admitted for moving the cylinder rearwardly to the groove 41, and groove 37, and by means of conduits grooves and ports through into the space 35 and front end of the tube 29. If only one path is required between the pump and pitch varying motor for pressure oil, an additional path being required for lubricating system pressure oil, the governor unit is replaced and tube 25 is removed and replaced by a modified type. Another type of tube is employed where no supply of oil is used at lubricating oil pressure but only a single high pressure system is used for the purpose described. Where the pitch varying mechanism is electrical the parts may be converted.