Patent GB-731518-A (GB)
Title: Improvements in and relating to the operation of hydraulically actuated reversible variable pitch propellers
IPC: B64C11/42
Filed: 1953-12-09
Abstract: 731,518. Variable pitch propellers. BLACKBURN & GENERAL AIRCRAFT, Ltd., TETLEY, R. C., and BATEMAN, J. E. Dec. 9, 1953, No. 34333/53. Class 114. In a system for operating hydraulically actuated reversible variable-pitch propellers in which the pitch varying mechanism is normally controlled by a constant speed unit 12 effective on the movable member 11<SP>1</SP> of a valve 11 between which and the pitch varying mechanism hydraulic liquid supply lines 18, 19 is a reversing valve 15, the arrangment being such that when it is required to reverse the pitch of the blades of the propeller the valve member 11<SP>1</SP> is displaced so that the constant speed unit 12 becomes ineffective thereon and the reversing valve member 16 is also displaced due to hydraulic pressure in lines controlled by three spring-loaded solenoid-operated valves 24, 25, 26 controlling respectively "reverse pitch", "coarse pitch" and "maximum pressure", the solenoid-operated valve 24 controlling the supply of pressure to displace the member 16 of the reversing valve receives such pressure through the second solenoid-operated valve 25 while the third solenoid-operated valve controls the creation of maximum pressure. To reverse the pitch of the propeller blades, switches 50, 51, 52 are closed to energize the solenoids of the valves 24, 25, 26 and raise their members 24<SP>1</SP>, 25<SP>1</SP>, 261 from the positions shown in Fig. 2. Oil from the engine is supplied by the booster pump 4 into conduits 7 and 20 thence via conduit 23, valve 26 and conduits 49 and 35 into valve 11 to raise the member 11<SP>1</SP>, whereupon the constant speed unit 12 becomes ineffective. Pressure liquid also flows from valve 26 and conduit 49 into conduit 31 to displace shuttle valve 29, allowing maximum pressure to build up in conduit 18. Pressure liquid also flows from conduit 20 via conduit 22, valve 25, conduit 47, valve 24 and conduit 42 to displace the valve member 16. Pressure liquid then flows from conduit 7 past the valve member 11<SP>1</SP> into conduit 13 thence through the valve member 16 into the fine pitch line 19 so to the blade-pitch controlling mechanism which displaces the blades beyond fine pitch to reverse pitch, the liquid in the coarse pitch line 18 flowing past member 16 to conduit 14 and past the member 11<SP>1</SP> into the low pressure conduit 10. Should valve 24 fail, although pressure supply to the line 42 is then cut off the reversing valve member 16 remains displaced since the valve member 25<SP>1</SP> blocks the connection between conduit 42, valve 24, conduit 48 and the drain line 32. Similarly should valve 25 fail, the reversing valve remains unaffected since the connection between conduit 42 and the drain via conduit 48, valve 25 and line 32 is blocked by the member 24<SP>1</SP>. If the valve 26 should fail this can have no more effect than a reduction in pressure since the valve member 16 can only make a return movement when the conduit 42 is connected to the drain through the valves 24 and 25.