GB659800A - Improvements in jet propulsion power plants for aircraft - Google Patents

Abstract

659,800. Jet propulsion plant. POWER JETS (RESEARCH & DEVELOPMENT) Ltd. March 15, 1946, No. 8096. [Class 110(iii)] To lessen the thrust at idling and the back pressure on the turbine during periods of acceleration, the power control lever of a gas turbine jet propulsion engine is connected to means for varying the jet characteristics i.e., pressure, quantity velocity or temperature of the jet, so that the thrust is minimised at low throttle settings and the turbine back pressure is temporarily reduced during power increasing movements only of the power control lever. The power control lever controlling the fuel supply to a gas turbine jet propulsion engine is connected to the lever 7 of a hydraulic transmitter 8, Fig. 2. On opening of the power control lever 7 moves in the direction indicated by the arrow and the cam 16 moves the piston 17 left to right admitting pressure fluid from the clearance 35 through the port 30 and non-return valve 42 to the gallery 24 from whence it passes through the ports 31 and 32 to the transmission line connected to the port 25. The clearance 35 is pressurised from the inlet port 22 through the gallery 21 and port 29. The transmission line is connected to the port 49, Fig. 3 of a receiver 11. Increased pressure in the transmission line causes the piston 47 to move against the action of a spring 58 and move the operating rod 53 of a variable area nozzle or spilling means so as to increase the area of the nozzle or to open the spilling means. The piston 47 is not connected to the rod 53. The pressure fluid passing through the port 30 also acts on the left hand face of the piston 20 and causes a follow-up sleeve 19 to move to the right but as the space to the right hand side of piston 20, which is connected through gallery 23 and port 28 with the annular clearance 34 between the sleeve 19 and piston 17, can only be drained through the interior of piston 17 and the bleed 37, port 27 being closed by the displacement of the piston 17, the movement of the sleeve 19 is delayed. Whilst the piston 17 and sleeve 19 are out of step, pressure is applied to the transmission line but when the sleeve 19 regains its original position relative to the piston 17, the pressure is cut off and the nozzle area returned to its original value by the action of the spring 58. The fluid from the receiver 11 and transmission line is drained through the ports 25, 32, 31, gallery 24, port 27 and bleed 37 so the return of the nozzle mechanism to its normal position is damped. On moving the power control lever to lessen the power, the piston 17 is displaced relatively to the follow-up sleeve 19 in the opposite direction and pressure fluid is admitted through port 28 and gallery 23 to the right hand side of piston 20 thus causing the follow-up sleeve to follow the piston. Since the space at the left hand side of the piston 20 is connected freely to the drain 40 through the ports 30 there is no delay in the follow-up movement. Moreover, since gallery 24 is no longer in communication with the pressure supplygallery 21 no pressure is applied to the transmission line. When the idling range of the power control lever is reached the distributer piston 38 comes into operation, the displacement of the follow-up sleeve 19 relatively thereto causing the port 31 to be closed and port 32 to be put into communication with the port 33 which is connected to the pressure gallery 21. The nozzle area is therefore increased or the spilling means opened. This action continues while the power control lever is in the idling range. The distributer piston 38 is flexibly attached to the adjusting-screw 43 which allows the idling range to be varied. The power control lever may also be arranged to bring into operation means for reheating the gases exhausting from the turbine when high output is required. When the reheat is turned on an increase of nozzle area is required. The receiver unit shown in Fig. 3 is therefore provided with a second cylinder 46 in which slides a spring-loaded piston 48. The piston 48 is loosely mounted on the operating rod 53 and bears against a collar 57 on it. The port 52 is connected to the downstream side of the reheat fuel supply cock so that when the reheat fuel is turned on pressure is applied to the left hand side of piston 48 which moves to the right and carries with it the rod 53 which opens the nozzle. The ignition of the reheat fuel may be effected by electrical means or by use of special igniter fuels which spontaneously ignite. Suitable igniter fuels are mentioned in Specification No. 659,795, [Group XI]. If a special igniter fuel is used this may be automatically injected by a small pump 66 having a plunger 67 operated by an extension 69 of the piston 48. At the same time, air is compressed between the piston 48 and the plunger 67 and when the plunger 67 is near the end of its stroke it uncovers a transfer port 73 and allows the compressed air to pass through the discharge port 71 and force the igniter fuel to the reheat burners. If electrical means of ignition is used, the compressed air may be used to raise a diaphragm to which is connected a contact which completes the circuit. The container in which the diaphragm is contained may have a bleed to atmosphere to limit the time of contact. Specifications 606.176 and 619,050, [Group XXXVI], are referred to.