Patent GB-558741-A (GB)
Title: Improvements in variable pitch airscrews
IPC: B64C11/42
Filed: 1942-05-08
Abstract: 558,741. Fluid-pressure servomotor-control systems. DE HAVILLAND AIRCRAFT CO., Ltd., and WARDE, R. H. May 8, 1942, No. 6267. [Class 135] In a variable-pitch airscrew incorporating a double-acting ram supplied with hydraulic fluid under the control of a governor-operated valve, for an under-speed condition one end of the ram is connected to a low pressure actuating fluid supply and the other end is connected to drain, whilst for an over-speed condition the one end is connected to drain and the other end is connected to a higher pressure actuating fluid supply. For feathering and/or reversing, high-pressure hydraulic fluid is supplied by an auxiliary high-pressure pump, and the governor-operated valve is then adjusted manually. In the form shown in Fig. 1, a hollow ported sleeve 7 driven by the engine defines four annuli 9 ... 12 and carries centrifugal weights 18 which operate against a spring 25 to move a valve spindle 19 having four lands 20 ... 23 and a port 24 connected by the sleeve 7 to the engine sump or other drain. The annuli 9, 12 are connected by conduits 17, 16 to the inboard and outboard ends 13, 15 of the ram 14, the annulus 11 is supplied with low-pressure engine oil, and the annulus 10 is supplied with engine oil the pressure of which has been boosted by a gear pump 27, 28. A spring-loaded valve 48 relieves excessive pressure of boosted engine oil. In the position shown, all the annuli are blanked off from intercommunication. An increase of speed raises the valve spindle 19 and boosted engine oil flows to the inboard. end 13 to coarsen pitch, the outboard end 15 being connected to drain by the raising of land 23. A decrease of speed lowers the valve spindle 19 and engine oil flows to the outboard end 15 to produce a finer pitch, the inboard end 13 being connected to drain by means of the port 24. The hollow feathering valve 37, Fig. 4, has lands 38- 40 and outlet ports 42, whilst its housing sleeve 33 has annuli 34-36. Engine oil flows through a through-port 31 at the gear pump inlet, a port 32, annuli 35, 44, 34 and port 45 to annulus 11. Boosted engine oil from the gear pump 27, 28 flows through a port 43, the back of sleeve 33, port 46, annulus 36, and port 47 to the annulus 10. For feathering and unfeathering operations oil is supplied by an auxiliary, preferably electricallydriven, high-pressure pump to the inlet 41 and pushes back the valve 37 against the action of a spring 49. The lands 38, 40 cut off the supply of engine oil and boosted engine oil from the annuli 11, 10, but feathering oil flows through ports 42, 46, annulus 36, and port 47 to the annulus 10. To enable feathering to be performed the valve spindle 19 is raised by rack-and-pinion gearing 53, 54, a spindle 52, and a manual control lever remotely actuated by the pilot. A down-limit stop 55 for the rack is provided on the spindle 52. For an unfeathering operation the engine is stopped so that the spindle 19 is pushed right down by the spring 25, and the auxiliary highpressure pump is operated until land 38 clears the port leading from the annulus 34, and feathering oil flows along port 45, through annuli 11, 12, to the outboard end 15.