Patent GB-927718-A (GB)
Title: Improvements in or relating to variable pitch propellers and propeller fans
Inventor: CHILMAN JOHN ALFRED
IPC: B64C11/40
Filed: 1958-12-04
Abstract: 927,718. Axial-flow fans. DOWTY ROTOL Ltd. Dec. 4, 1959 [Dec. 4, 1958], No. 39114/58. Class 110 (1). [Also in Group XXXIII] A propeller fan installation comprising a propeller and driving means therefor has manually-operable means for varying the pitch of the propeller blades and pitch limiting means connected to the driving means and operating when the latter operates at a pre-selected operating condition to limit movement of the blades in at least one direction. The propeller is driven by a gas-turbine engine 14. The hydraulic pitch change motor 9 has a piston member 36, connected to the blades 13. Conduits 34, 35 extend through the piston member to the fine and coarse pitch sides of the motor and a control valve element 30 is slidable relative to the said member 36 to connect a pump 32 selectively to said fine and coarse pitch conduits. The element 30 is moved by a lever 27, about a fixed pivot 28 by means of a member 25 connected to the piston 22a of an hydraulic servomotor 22, and having pivoted thereto at 40 a manual control lever 37 pivotally mounted at 38. Automatic pitch adjustment of the propeller is controlled by a variable datum constant speed unit 17 incorporating a speed governor 18 and a valve 19 whereby fluid from a pump 20 is delivered via either pipe 23 or 24, depending upon the nature of the pitch change; to the servomotor 22, causing movement of member 25, lever 27 and valve element 30 which controls the supply of fluid from pump 32 to move piston member 36 to alter the pitch of the blades 13, the member 36 following up movement of element 30 to cancel pitchchanging movement upon attainment of the pitch-changing demanded by the element 30. The lever 37 follows movement of the element 30, and is indicative of the governing function. When it is desired to change to manual control, the pilot lifts a lever 41 thereby closing a switch 42 to actuate a solenoid-operated valve 45 which opens a by-pass conduit 52 to permit free-stroking of the piston 22a. Pitch adjustment may then be performed manually by movement of lever 37 about its pivot mounting 38. To prevent the pilot selecting too fine a pitch a device 16 is employed. When said device detects a pre-selected condition of underthrust, under-torque or overspeed, it causes current to flow through circuit 50, 51 to energize a solenoid 49 so that a pawl 48 engages a ratchet 47, on a shaft 46 coaxial with pivot 38 and formed integrally with the lever 37, thereby preventing further movement of the lever in the pitch-fining direction. The ratchet still permits adjustment in the pitch-coarsening direction. The device 16 may be interconnected with the engine fuel system. Since overcoarsening under manual control may stall the engine, the device 16 may alternatively be arranged to operate upon detection of a preselected condition of over-thrust, over-torque or under-speed, the ratchet wheel 47 then being of opposite hand. The device 16 and the pawl and ratchet may be duplicated to impose limitations on the manual control in both the pitch-fining and pitch-coarsening directions. Specification 715,133 is referred to.