Patent GB-445640-A (GB)
Title: Improvements in or relating to controllable pitch propellers
IPC: B64C11/44
Filed: 1935-03-08
Abstract: 445,640. Screw propellers. STEVENS, A. H., 5, Quality Court, Chancery Lane, London.-(Aviation Manufacturing Corporation; 927, Market Street, Wilmington, Delaware, U.S.A.) March 8, 1935, No. 7307. [Class 114] [See also Group XXXV] A variable-pitch screw propeller in which the adjusting gear is engageable and disengageable is provided with electromagnetic means for setting the gear, such means being stationarily mounted. Blades 18 are mounted in sockets 20 in the hub and carry worm wheels 21 which are driven through other worms and across shaft 23, carrying a pinion 22. The pinion 22 is adapted to engage right and left handed threads 33, 34 on a sleeve 32 which is slidable axially but is non-rotatable. This sleeve is supported in an extension 35 of the engine boss. Pins 35a fixed in the casing 35 extend through helical slots in the sleeve 32. Inside the sleeve is a rotatable ring 38 which is held against axial movement by the pins 35a which extends into straight slots 39 therein. An arm 40 is fixed to the ring 38 and extends through the sleeves to a slidable rod 43 which is coupled to the pivoted levers 44, 48 which in turn are connected to the rods 46, 51 of solenoids 36, 37. Spring return means 55 and centralizing pin 115 are provided. When either solenoid is energized, the rod 43 is moved lengthwise, whereby the pin 40 rotates the sleeve 39 and the sleeve 32 is slidden so that either the thread 33 or 34 engages the pinion 22 and the blades receive a corresponding adjustment. In a modification, two solenoids may be supplied for each pivoted lever, the second solenoids being employed to return the gear to neutral. A pitch indicator 94 is moved over a scale 93 by a screw rod 96, rotation of which through gear-wheels 74 or 77 is affected by clutching them to a shaft 70 driven off the engine. A method of clutching consists in the use of solenoids 84, 86, which are operated in synchronism with the main solenoids 36, 37. At either end of its travel the indicator extension 103, contacts with switches 107, 106 which cut out the solenoids and prevent overrunning of the pitch adjustment. The apparatus may be arranged to act automatically by the use of a generator 118 driven by the engine or propeller shaft at a speed proportional to the engine speed. This generator has voltages approximating to a straight line function of the speed. A torque type relay 120 with a permanent magnet 121 is employed, the oscillatory armature 122 with a winding 124 being connected by conductors 125, 126 to the field winding 119 of generator 118. The contact arm 123 is held under normal engine speed in neutral position. Change in speed alters the voltage and shifts the contact 123 to engage contacts 127 or 128 which establishes the circuit for the solenoids which put into engagement the pitch changing gear. A rheostat 132 is included whereby current to the relay may be varied to establish desired engine speed. For hand control, the switch arm 140 is moved from the lead 142 and then positioned over 141 or 143 or placed in an open neutral position.