Patent GB-525809-A (GB)
Title: Improvements in and relating to variable pitch propellers
IPC: B64C11/42
Filed: 1938-11-07
Abstract: 525,809. Air compressors. ALGARSSON, G. Nov. 7, 1938, No. 4881/40. Divided out of 522,249, [Group XXXIII]. [A Specification was laid open to inspection under Sect. 91 of the Acts, May 16, 1939.] [Class 8 (i)] [Also in Group XXXIII] The blades of a variable-pitch air screw are connected to a statically mounted fluid pressure device drivably associated with the air screw, the torque transmitted through the device being controllable both in magnitude and direction to effect variation of pitch. The air-screw blades 23, 25, Fig. 1, are interconnected by bearings 26 between a pin 27 and sleeve 29 and are supported by bearings 31. Each blade has a bevel gear 34 carrying a counterweight 37 and gears with a bevel gear 36 gearing with compound wheels 39, 40, on a planetary ring 41. The latter gears with a compound wheel 42, 43, carried by the hub casing. The gear 43 engages a gear 44. Relative movement between all these gears occurs only during pitch changing. The gear 44 is connected to a statically mounted air motor 58 by gearing 51, 54. The motor 58 has four radial cylinders 62, the crank casing acting as a discharge manifold and being connected to a pipe 74. Each piston acts as a slide valve, without lap or lead, to control the working fluid to an adjacent cylinder, the intake manifold 71 being connected to a pipe 70. A compressor 68 is identical in construction with the motor 58, but runs at about twice the speed and supplies compressed air to the pipe 70. The pipe 74 and a byepass 72 from the pipe 70 lead to outlet ports 77, 78 controlled by valves 73, 75 under the action of a speed governor 76 driven by the engine. In operation, upon increase of engine speed above the normal desired, the governor 76 opens port 77 and closes port 78. The motor 58 then acts as a compressor and causes a drag on the gear wheel 44 which is transmitted through the epicyclic gearing to the bevel wheels 34 to turn the air screw blades to a higher pitch. If the engine speed falls the port 77 closes and the port 78 is opened, and the motor 58 is driven by the compressed air and the air screw blades are moved to a lower pitch. The governor is adjusted by a remotely controlled worm 80 to maintain any desired speed. To set the blades to the feathered position, i.e., high pitch, the pilot closes the throttle and operates the lever 81 to open port 77 and close port 78. In the event of engine stoppage, the blades may be turned to the feathered position by operating lever 81 and by putting the pipe 74 into communication with a compressed air reservoir 86. In a modification the compressor 68 is omitted. In a further modification the motor 58 and compressor 68 are replaced by hydraulic gear pumps 93, 94, Fig. 11. The pipe lines 70, 74, are similar and relief valves 95, 96 are inserted. The outlets 99, 100 from the governor 76 are led by a pipe 97 to the intake 98 of the compressor 94. Specification 522,249, [Group XXXIII], is referred to. In the Specification as open to inspection under Sect. 91 a modification is referred to in which the motor 58 and compressor 68 are replaced by dynamo electric machinery and in which the valve controlled ports 77, 78 are replaced by electrical equivalents. This subject-mater does not appear in the Specification as accepted.