GB727096A - Device for feathering the blades of a propulsion unit on a multi-propeller aircraft - Google Patents

Abstract

727,096. Variable pitch propellers. SOC. NATIONALE DE CONSTRUCTIONS AERONAUTIQUES DU SUD-OUEST. March 9, 1953, No. 6471/53. Class 114. A device for feathering the blades of a propulsion unit on a multi-engined aircraft comprises two total pressure intake members 4, Fig.. 1, disposed in the slipstream of two of the units 2, the pressure members being connected to the inlets 47, 48, Fig. 3, of the two compartments of a differential pressure detector 6, the compartments being separated by an elastic diaphragm which actuates control members, one or other of which operates one or other of the devices for feathering the propulsion units. The device is particularly intended to operate in the case of engine failure during take-off. The differential pressure detector comprises a frame 18 clamped between an end plate 16 and cover.17, and having clamped to it by a ring 19 an elastic annular member 20 carrying a piston 21. The piston is supported by leaf springs 24, depending from the frame 18 and ring 19 respectively, through a rod 23 having a flattened end portion 23a formed with upper and lower projections 27, 28 which selectively engage one or other of micro-contacts 33, 34 when the diaphragm is displaced by a pressure difference, i.e. when one of the propulsion units fails. Assuming the contact 33 to be thus closed, current flows from a positive source 59, Fig. 5, through the micro-contact 33 to a visual indicator 62, whereupon the pilot depresses a "feathering" button 81 closing a circuit which includes a relay 67. There are duplicate circuits, one for each engine; only one circuit will be described. The relay closes a switch 66 completing a circuit to earth which includes the micro-contact 33, a lead 63 and a relay 64 adapted to close two switches 68, 69. The switch 68 permits excitation of a relay 82, the path to earth being completed through leads 83 and 72 and a "de-feathering" button 73. The relay 82 opens a switch 87 in the propeller pitch motor control circuit putting the control out of action; a device 89 gives visual indication of this. The switch 69 provides a path to earth for the relay 64 independent of the feathering button 81. If the engine is running at full power, e.g. during take-off the wide-open throttle closes a switch 84 between the relay 82 and a relay 85 which closes a switch 90, in a circuit fed at a much higher potential than the other circuits, this supply actuating the feathering devices in the propeller through a slip ring 55. This circuit is connected through a resistance 98 with the relay 85 rendering its excitation independent of the throttle controlled switch 84: the pilot can thus re-assume control of the engine's safety devices. If the failure is only momentary and the engine picks up again, the pilot depresses the " de-feathering " button 73, relays 85, 82 and 64 are de-energized and the switches they operate return to their normal positions, the pitch motor setting the blades at the "fine" position. When the engines are stopped, the visual indicators 62 may be tested by depressing a test button 79 in shunt with the micro-contacts 33, 34. A manually operated switch 94 permits either propeller to be feathered directly at the instance of the pilot. The pressure intakes may be heated by resistances 15, Fig. 6, arranged in parallel and provided with a visual indicator 106 indicating normal working and two differently coloured indicators 107, one for each resistance, which light up if the associated resistance fails. In the case of a threeengined aircraft, a differential pressure detector is arranged between each two adjacent engines, the pressure intake of the central engine thus communicating with both detectors 117, 118, Fig. 7. Each chamber of each detector has four contact studs, one pair, e.g. 121d being connected together and to the associated feathering circuit, while of the other pairs, all the outer ones are connected together and to the supply main while the inner ones of each detector are connected to each other. The application to a four-engined aircraft is also described. The device may be applied to turbo-jet units having adjustable blading to reduce the interval drag.