Patent GB-676039-A (GB)
Title: Tailpipe burning or afterburning control for turbojet engines
IPC: F02K1/16
Filed: 1950-02-21
Abstract: 676,039. Gas turbine jet propulsion plant. BENDIX AVIATION CORPORATION. Feb. 21, 1950 [March 22, 1949], No. 4457/50. Class 110(iii) [Also in Group XXIX] A gas turbine, jet propulsion engine in which the thrust is augmented by reheating of the turbine exhaust gases, has means responsive to an engine operating condition for varying the rate of flow of afterburning fuel and a device for varying the effective area of the jet. In the arrangement shown, Fig. 1, fuel is supplied to the main burners 15 by a pump 35 through a control mechanism 33 and to the reheat burners 167 by a variable delivery pump 123. In the event of failure of the control mechanism 33 fuel may be supplied to the main burners through an engine driven pump 41, byepass conduit 43 and double check valve 44. The control mechanism 33 is regulated by the pilot's throttle lever 45 which has a projection 50 movable in a slot 51 which slot has an extension 52 into which the projection 50 is moved when it is desired to supply fuel to the reheat burners. When this is done the projection 50 depresses a switch plunger 53 and energizes a circuit formed by the wires 58, 59 and 59<SP>1</SP>. This allows, power to be supplied to the igniter 170 and airspeed responsive device 60. The airspeed responsive device 60, Fig. 2, comprises a pair of bellows 61, 62 arranged in opposition and suitably anchored at 63, 64, the bellows 61 communicating with a pilot tube through a conduit 65 and the bellows 62 with a static pressure source through a conduit 66. To balance out the effects of air density or altitude the bellows 61, 62 are opposed by a pair of evacuated bellows 71, 72. The bellows 61 actuate a pivoted lever 75 direct through a member 68 and the bellows 62 actuate the same lever through a pivoted arm 85 and an adjustable slide rod 88<SP>1</SP>. The free end of the lever 75 engages a pin 79 on one arm of a bell-crank 78, the other arm 78<SP>1</SP> of which passes over a contact segment 82 having an insulated section 83 and a conducting section 84. If the speed of the aircraft is below a predetermined value, the arm 78<SP>1</SP> contacts the section 84 and energizes one element 94 of a thermostatic switch 95 located at the rear end of the tail pipe 20 and a solenoid 107 of a normally closed valve 108. Energization of the solenoid 107 opens the valve 108 and allows compressed air from the compressor discharge to act on spring-loaded bellows 114 which partially collapse and in so doing rotate the cam plate 118 clockwise. This cam plate actuates the lever 122 of the fuel pump 123 and causes fuel to be supplied to the burners 167. The valve 140 is normally open to atmosphere so that the pressure acting on the bellows 114 at this stage is intermediate between the compressor discharge and atmospheric pressures. The value of this pressure is determined by the size of the orifices 119, 142. The fuel supplied to the burners 167 is ignited by the ignitor 170 and the resulting temperature rise in the tail pipe 20 causes the element 94 to contact the element 96 of the switch 95. This allows current to flow through the solenoid 98 of the switch 99 and the switch member 100 to bridge the contacts 102, 103, 104. The current supplied through contact 103 energizes a solenoid 137 and causes a valve 140 to close. This allows the full compressor discharge pressure to act on the capsule 114 which collapses still further and increases the fuel supply to the burners 167. The current supplied through contact 104 energizes the solenoid 144 and causes the valve rod 146 to move to the right against the action of the spring 149 and compressed air from the compressor discharge to be supplied to the right-hand side of the servo-motor piston 31 and open the leaves 23, 24 of the variable area nozzle 22. The opening of the leaves 23, 24 acting through the levers 128, 130, 132 and 133 compresses the spring 127 and causes the cam follower 120<SP>1</SP> to be urged against the inner contoured surface of the cam 118 which determines the relationship between rate of fuel feed and the crosssectional area of the nozzle. The return of the lever 45 to its normal position causes the switch 53 to open and the parts to return to the normal position as shown. A modification in which the pump 123 is replaced by a constant discharge pump with a byepass back to its suction is also described. In this arrangement the bellows 114 control a valve in the byepass and the lever 132 operates a throttle valve in the discharge of the pump. An additional solenoid operated valve, arranged electrically in parallel with the valve 108, is placed in a byepass around the throttle valve so that when energized it allows sufficient fuel to pass to the burners 167 for starting purposes. The burners 167 may be of the constant pressure discharge type and are arranged downstream of a number of baffles 168.