Patent GB-614951-A (GB)
Title: Improvements in or relating to variable pitch propellers
IPC: B64C11/30
Filed: 1946-06-25
Abstract: 614,951. Variable-pitch propellers. ROTOL, Ltd., MORRIS, E. H., DANVERS, E., and GODDEN, T. E. June 25, 1946, No. 19028. [Class 114] In a reversible, variablepitch propeller comprising a pitch-change mechanism 6, means 59 for normally limiting the movement of the blades to within the positive pitchrange, and a constant-speed unit 14 for automatically regulating the pitch-change mechanism in the positive and negative pitch ranges, a manual control 17 is connected for over-riding the constantspeed unit so that it operates the pitch-change mechanism to move the blades to within the negative. pitch-range and for simultaneously removing the blade-movement limiting means. The control 17 is connected through a linkage 18 with an axially adjustable sleeve 19 for adjusting the loading on the governor spring 22 of the unit 14. Liquid to operate the mechanism 6 is supplied by a pump 12 fitted with a spring-loaded relief valve 39, and a feathering pump 16 is also provided. The control 17 is shown in the position C corresponding to slow running of the engine, and the ram 7 of the pitch-change mechanism is against stops 59, the blades being at zero pitch. The stops 59 comprise resilient fingers which normally collapse inwardly but are maintained outwardly by a spring-loaded abutment 64. When the control 17 is moved to its full power position A and the speed of the plant exceeds the datum speed for which the unit 14 has been adjusted, liquid is supplied from the pump 12, past the valve 13 of the constant speed unit and a valve 36, through pipe 64 and to the left of the ram 7 so that the latter moves clear of the stops 59 and adjusts the blades to a coarse pitch position, this position being controlled by the unit 14 according to the datum setting corresponding to the position of the control 17 along the slot 23. If, with the parts in the position shown, the control 17 is moved through the gate 25 towards the full power position B, an arm 4 of an electric switch is moved to engage a contact 42, thereby energizing solenoids 35, 37 to raise valves 27 and 28 respectively. Liquid in pipe 31 from the pump 12 flows through valve 27 to actuate a motor 29 which overrides the valve 13 and through valve 28 to motors 32 and 33, the former increasing the load on the relief valve 39 and the latter raising the valve 36 which transposes the connections to the mechanism 6. Liquid at increased pressure then flows from the pump 12, through valves 13 and 36 into pipe 54 to the right-hand side of the ram 7 and to passage 55 to open a normally closed spring-loaded valve 56 and thence into a space 63, thereby moving abutment 64 to allow stops 59 to fall inwardly. The ram is then free to continue its travel to the left and the blades enter the negativepitch range until a pin 53 engages a spring- loaded rod 52 to actuate a slide 48 which moves an electric switch 45 to engage a contact 47, thereby de-energizing the solenoid 35 so that the unit 14 is free to assume control again, the solenoid 37 remaining energized. In a modified embodiment in which the unit 14 is normally adjusted by the control 17 as described above, a manual speed control is added which is capable of over-riding the control 17.