Patent GB-548833-A (GB)
Title: Improvements in or relating to variable-pitch airscrews
IPC: B64C11/44
Filed: 1941-04-23
Abstract: 548,833. Screw propellers. BRISTOL AEROPLANE CO., Ltd., THOMAS, F. M., KENNEY, D. J., and PRICE, P. R. April 23, 1941, No. 5261. [Class 114] In electrically-operated pitch-change arrangements for airscrews comprising a governor-controlled motor, additional means is provided for increasing the rate of pitch-change beyond the maximum governor-rate when the speed-deviation of the airscrew exceeds a predetermined amount. The arrangement shown in Figs. 2 and 3 includes a reversible pitch-change motor 10 driven by a battery 14 and having windings 11, 12 in circuit with contacts 22, 23 which are vibrated by a cam 63 and co-operate with a contact 21 carried by a member 24 controlled by a hydraulic governor 25. If the speed is too high or low, the contact 21 engages the contact 23 or 22, the circuit of the battery is completed, and the motor turns the blades towards coarse or finepitch position. The arrangement is now modified by providing the member 24 with a finger 33 for closing contacts 29, 30 and 31, 32 in circuits including the battery 14, a motor-generator 34, 35, and solenoids 46, 48 and 39 for closing contacts 41, 45, 40, 44, and 38. The contacts 29, 31 may be merged. When the speed rises abnormally, the contacts 29, 30 are closed by the governor, the contacts 41, 45 are closed by the solenoid 46, the contacts 38 are closed by the solenoid 39, the motorgenerator starts, and the voltage applied to the motor 10 is considerably increased. Similarly, when the speed falls abnormally, the contact 32 is closed, and the voltage applied to the motor is considerably increased. In another arrangement, a power-driven generator is substituted for the motor-generator 34, 35. In the arrangement shown in Fig. 5, a power-driven generator 50 of the same voltage as the battery 14 is normally in parallel therewith, but is placed in series when abnormal speed-change occurs. For this purpose, the solenoids 46, 48 control the contacts 41, 45 and 40, 44 only, and an auxiliary switch 51, operated by a solenoid 52 and carrying contacts 54, 55, 56, is provided. Normally, the generator and motor are in parallel, the positive and negative poles being connected through the contacts 55, 54. When an abnormal speed-change occurs, one of the solenoids 46, 48 is energised, the switch 51 is depressed, and the motor-circuit passes through the negative pole of the generator, contacts 57, 58, the negative pole of the battery, contacts 61, 62, and one or other of the contacts 40, 41. The generator may be replaced by a battery, preferably arranged in sections which are connected in parallel or series for normal or abnormal operation. In another arrangement, shown in Fig. 7, the above-described governor-contacts 29 .. 32 are omitted, and the cam 63 is associated with a second cam which has lobes and hollows of greater extent than the cam 63 and operates contacts 68, 69 arranged between contacts 70, 72 and 71, 73 and connected to the contacts 22, 23. The contacts 72, 73 and 70, 71 are in circuit with contacts 80, 81, and solenoids 75 ,76 provided with contacts' 78, 79. Under normal governor-control, the contacts 68, 69 engage the contacts 70, 72 when one of the contacts 22, 23 has engaged the contact 21. If an abnormal speed-decrease occurs, the contacts 21, 22 are not broken when the contacts 68, 69 descend, and when these contacts engage the contacts 70, 71, a circuit including the battery 14, contacts 21, 22 and solenoid 75 is completed. Thereupon the contacts 82 are closed to complete a circuit including a generator 75 and the winding 11, and a high voltage is applied to the motor. Similarly, if an abnormal speed-increase occurs, the solenoids 76 and winding 12 are energised, and a high voltage is applied to the motor. To prevent breaking of the motor-circuit when the contacts 68, 69 are again moved, a cam-operated detent locks the contact 78 or 79 before the contacts 22, 23 leave their datum position.