Patent GB-775457-A (GB)
Title: Improvements in or relating to electrical control system for reversing and feathering propellers
IPC: B64C11/30
Filed: 1954-09-28
Abstract: 775,457. Variable pitch propellers. UNITED AIRCRAFT CORPORATION. Sept. 28, 1954 [Oct. 1, 1953], No. 27956/54. Class 114. A variable pitch propeller, hydraulically operated, comprises a governor controlling the supply of fluid thereto, a feather-unfeather switch having a holding coil for its feathered position in which position the switch connects one side of the coil to a source of energy, a switch actuated by pressure of fluid in the governor and connected to the other side of the holding coil to complete the circuit from there and the source of energy, and a switch on the propeller blade arranged in parallel with the pressure-actuated switch to complete a circuit parallel to the above-mentioned circuit, the blade switch breaking its portion of the circuit adjacent the feathered position of the propeller at the feathered position thereof. Feathering. On pushing in a featherunfeather button 54, a contact bar 64 bridges contacts 58, 60, 62 and a bar 72, contacts 74, 76. A battery 66 connected to the contact 62 then directs current through the contact bar 64 and contact 60 to a relay 70 associated with the motor 32 of an auxiliary pump 34 ; the relay closes the circuit to the motor from the battery 66. The bar 64 in contacting the point 58 excites a holding coil 68 retaining the bar in the " feather " position when the button 54 is released. The holding coil has two parallel paths to earth, one through the contact 74 and a cut-off switch 40 actuated by a surge of pressure when the " feathered " position is reached, and the other through the contact 76 and a switch 48, on a propeller blade 12, which cuts out about 10 degrees before the full feathering position. Both switches being cut off at this full position, the holding coil 68 is de-energized and the contact bar 64 returns to the neutral position shown, the break at the contact 62 deenergizing the relay 70 to open the circuit between the battery 66 and the auxiliary pump motor 32. Pulling the button 54 to the right bridges contacts 84, 82, 80 and 78, the former two being permanently connected to the contacts 62, 60 to actuate the relay 70 as before. Of the other contacts, 78 energizes a relay A connected to earth through a blade switch 44 to close a switch 88 and energize a solenoid operated decrease pitch valve 38. On releasing the button 54, the blade switch breaks the circuit as the blade enters the governor controlled range ; if the button is still held out, the fluid pressure from the pump makes the blade oscillate about the point of interruption. Reversing. A throttle control 106 carries a cam 110 with a lobe 112 adapted to depress a plunger 122 which through an anvil 236, Fig. 3, and a pair of flat plates 121, 123 actuates simultaneously four snap-action switches E<SP>1</SP>, E<SP>2</SP>, S<SP>1</SP>, S<SP>2</SP> mounted side by side on the throttle quadrant. The switch E<SP>2</SP> brings into circuit the switch E<SP>1</SP> closure of which excites a relay F actuating a switch 132 to connect the source of power 66 to the relay 70 of the switch controlling the auxiliary pump motor 32 to start the motor. Simultaneously the switch S<SP>2</SP> connects up the solenoid of the decrease pitch valve 38 so that the pressure fluid moves the blade towards the " reverse " position. The switch S<SP>1</SP> is normally earthed ; actuation of it connects the relay F to earth through a switch 52, Fig. 1, on the propeller blade 12 controlled by the angular position of the blade. When the " reverse " position is reached, an insulated part 46 of the blade switch contacts the part or brush 52, the circuit through the relay F is broken, the switch 132 opens and the supply to the auxiliary pump motor 32 is cut off. To restore positive pitch the lobe 112 is moved off the plunger 122 the flat plate 123 swings back and the switches S<SP>1</SP>, S<SP>2</SP> are opened. The switch E<SP>1</SP> being directly grounded provides a path for the relay F which closes the switch 132 to start the auxiliary pump motor 32. Opening the switch S<SP>2</SP> disconnects the solenoid of the decrease pitch valve 38 so that the pump pressure increases the pitch. During this time, the flat plate 121 controlling the switches E<SP>1</SP>, E<SP>2</SP> is held by a latch 134 actuated by a magnet 142 the circuit of which is completed by a blade switch 42, 50 arranged to pass current when the blade reaches the governor-controlled range of pitch. Excitation of the magnet coil 142 withdraws the latch 134 and the switches E<SP>1</SP>, E<SP>2</SP> open, interrupting the flow through the relay F and stopping the motor 32. The pitch is now governor-controlled as described in Specification 683,888. Specification 775,458 also is referred to.