Patent GB-798514-A (GB)
Title: Control systems for multi-engine aircraft employing reaction jets
Inventor: SKELLERN JOHN
IPC: F02K99/00
Filed: 1955-12-14
Abstract: 798,514. Gas turbine jet-propulsion engines. NAPIER & SON, Ltd., D. Nov. 30, 1956 [Dec. 14, 1955], No. 35946/55. Class 110 (3). [Also in Group XXIX] In a control system for a multi-engine aircraft in which the gas streams delivered by two or more engines enter a common duct leading to one or more jet-propulsion nozzles, a device sensitive to a difference in the gas discharge conditions between two or more engines is provided, the device being arranged automatically to isolate from the common duct an engine of which the regulating parameter to which the device is sensitive alters by a predetermined amount from the value given by the remaining engine or engines. The device may be sensitive to a difference in the speeds of the engines and arranged automatically to isolate from the common duct an engine whose speed falls to a predetermined extent below that of the remaining engine or engines. Each engine may drive a rotary member, for example a fuel pump, which generates a fluid pressure which is a function of the speed of rotation of the engine, a device being provided which balances these pressures against each other and which is moved in the event of an unbalance in these pressures, to influence hydraulic actuating mechanism for an isolating valve which isolates from the common duct the engine responsible for this unbalance. The invention is shown applied in the case of a jet-propelled helicopter having two gas turbine engines only one of which A, is shown in Fig. 2, which supply a mixture of combustion gases and air to the common duct 18, the air and gas mixture then flowing through trunk 20 and the hollow rotor blades 21 to jet-propulsion nozzles 22 at the blade tips. Each engine comprises an air compressor 10A, combustion equipment 11A, and gas turbine 13A, the turbine driving the compressor 10A and also a second compressor 15A, the latter discharging to a chamber 14A where the air delivered thereby is mixed with exhaust gases from the turbine. The mixture of air and gases then flows through duct 16A to an isolating valve 17A from which the mixture flows either to the common duct 18 or directly to atmosphere through duct 19A depending on the position of the valve. Each propulsion nozzle 22 has a device 23 for varying the area thereof, the device 23 being operated by means of a servomotor 27A through linkwork 24, 25, 26A, the servomotor also actuating the isolating valve 17A by means of the link 26A. A differential speed-sensing device 42 is provided and comprises two diaphragms 43, 44 which act through pins on to a pivoted arm 45. The spaces above and below the diaphragm 43 are connected through ducts 41A, 40A to the output and input sides respectively of the gas turbine engine fuel pump 38A. The spaces on either side of the diaphragm 44 are likewise connected to the fuel pump of the engine B. Should the speed of the engine A fall below that of engine B, the pressure difference between the ducts 41A and 40A will decrease whereby the resultant downward force on the diaphragm 43 will be reduced, the lever 45 thereupon swinging upwards. The lever 45 is disposed between two trigger valves 46A, 46B and the upward movement of the lever 45 causes the valve 46A to move upwardly whereupon fluid under pressure in the duct 48A (supplied from pump 30A through an hydraulic pressure accumulator 32A) is admitted through the duct 50A to raise the auxiliary shuttle valve 51A. Upward movement of the valve 51A permits fluid under pressure in the duct 48A to flow through the duct 52A to the left-hand side of the main shuttle valve 28A, this valve thereupon moving to the right against the action of the spring 29A and allowing fluid under pressure in the duct 33A to flow through the duct 36A to the right-hand side of the servomotor piston 27A which thereby moves to the left and causes the link 26A to move to the right thereby moving the isolating valve 17A to isolate the engine A from the common duct 18 and at the same time moving the devices 23 to the small area position. The isolating valve 17B associated with the engine B is controlled in a similar way. The main shuttle valve 28A may be moved to the right by means of a pilot's control lever 35A whereby the valve 17A is moved to the isolating position and the devices 23 to the small area position, but the normal positions can only be restored by the automatic control. Linkwork is also provided (not shown on Fig. 2) interconnecting the fuel metering unit 39A of the engine A with the link 26B of the other engine B, and similar linkwork interconnecting the fuel metering unit of the engine B with the link 26A of the engine A. In the event of isolation of an engine from the common duct therefore, the other engine is automatically adjusted to produce a higher output so as to compensate at least partially for the reduction in available power caused by the isolation. Specification 798,515 is referred to.