Patent GB-922255-A (GB)
Title: Improvements in and relating to control method and system for aircraft powerplants comprising a gas turbine driving a variable pitch propelling device
IPC: B64C11/30
Filed: 1961-03-21
Abstract: 922,255. Gas turbine plant. J. SZYDLOWSKI. March 21, 1961 [March 25, 1960], No. 10347/61. Class 110 (3). [Also in Group XXXIII] A control method for aircraft power plants comprising a gas turbine drivably connected to a variable pitch propeller or to a helicopter rotor consists in maintaining the turbine rate of revolution constant by means of a tachometric metering of the quantity of fuel delivered to the engine, simultaneously and continuously comparing, on the one hand, the actual rate of fuel flow with the theoretical maximum and minimum rates of flow that can be applied to the turbine and, on the other hand, the actual temperature of the gas on exit from the turbine with the preselected maximum permissible temperature of that gas, controlling the propeller pitch or the rotor collective pitch, either manually, without any form of mechanical stop between the minimum and maximum permissible pitches, or automatically, in terms of the result of said comparisons, and, in the case of a propeller, in effecting an automatic setting of the pitch should the tachometer metering system become momentarily inoperative in flight, except in cases where a reduction in pitch is commanded or the propeller is set at zero-thrust pitch. The turbo-propeller comprising a compressor 1, turbine 2 and propeller 3 with blade pitch controlled by electric motor 4, is controlled by an engine speed control throttle lever 5 associated with a pump 7 drawing fuel from a tank 8 and delivering it to a conduit 9, and blade pitch control lever 6, with extension 48 operating contacts 49, 50 in the low and high-pitch circuits of motor 4, fitted to shaft 45 carrying a disc 35 to which the blade pitch variations are transmitted by a cable 36 over pulleys 37, 38, 39, the pulley 38 having a cam 40 operating microswitch 41 open at maximum reverse pitch and closed from maximum reverse to feathered, a microswitch 42 closed at zero-thrust pitch, a microswitch 43 open between maximum reverse and normal pitch and closed between normal pitch and feathered, and a microswitch 44 closed from maximum reverse pitch onwards and opened when feathered position is reached. Into the conduit 9 is inserted a fuel metering device 17, the degree of opening of which is controlled by a tachometer unit 18 coupled to the turbine through a drive 19. This rotational speed regulating device 18 is of the type described in Specification 860,283, incorporates an isodromic regulator, and is equipped with an overspeed safety device 157. The rotational speed setting lever 20 is connected via linkage 21 to the throttle lever 5, and a pressure bleed control lever 158 is connected via a drive 27a to a lever 27 which actuates a reversing switch 29. The pressure bleed enables oil to be delivered to the propeller via a line 159, providing the turbine is rotating, so that oil pressure may prevail in the regulator 18. The lever 158 therefore provides an hydraulic propeller feathering device enabling the propeller to be feathered in an emergency by operation of the lever 27. A device 110, which senses, via passageways 111, 112, the air pressures P1 and P2 on entry into and on exit from the compressor 1, controls the displacement of a metering device 113 in the conduit 9, the fuel pressures pic and p2c upstream and downstream of this metering device being communicated via passageways 115, 116 to a comparator 114 connected by electric cable 117 to a circuit 30a which couples a temperature regulator 30 and the pitch control lever 6 to the blade pitch varying motor 4. The regulator has a potentiometer 31 set to the temperature which is not to be exceeded by the gas on exit from the turbine, and is provided with indications of the actual temperature of the gas as it exhausts from the turbine by thermocouples 33 inside the exhaust nozzle 34. The device 157 includes a piston having a tapered controlling section inserted in the conduit leading from the fuel pump 7 to the turbine injector nozzles, and electric contacts which in the event of a steep let-down or a dive are closed to complete circuits 36m-37m connected to the circuit 30a to cause pitch coarsening. A propeller thrust detector 141 has a passageway 142 in communication with the air clear of the propeller and a passageway 147 in communication with the air behind the propeller, the difference in pressure between the two being employed to actuate switches in cable 160 connected to the circuit 30a. The electric motor 4 controlling the blade pitch therefore receives its commands from either the comparator 114, the temperature regulator 30, the devices 141 and 157, or the pitch control lever 6, depending on the mode of operation. The electro-mechanical equipment is somewhat similar to that in Specification 914,188.