Patent GB-1126809-A (GB)
Title: Gas turbine engine
Inventor: CROSS WALTER GEORGE
IPC: F02K1/16
Filed: 1967-07-04
Abstract: 1,126,809. Gas turbine jet propulsion plant. ROLLS-ROYCE Ltd. July 4, 1967, No. 30817 /67. Heading F1J. [ Also in Division G3] A gas turbine engine having reheat combustion equipment and a variable area propulsion nozzle actuated by a power operated device includes a pressure responsive device which during reheat operation normally controls the power operated device in functional dependence upon the jet pipe pressure, means for supplying fuel to the reheat combustion equipment under the control of a manually operable member, and control means, effective only during a predetermined period initiated by predetermined movement of the manually operable member, for preventing the pressure responsive device from controlling operation of the power operated device and for ensuring that the latter is controlled by means of the manually operable member. A gas turbine jet propulsion engine 10, has a variable area nozzle 35 controlled by an axially movable sleeve 32 actuated by rams 26. A unit 23 controls the supply of fuel to pilot and main reheat burners 22, 21 respectively in response to engine variables and the setting of pilot's lever 92, ignition of the pilot burners being effected by a hot streak injector 25. During normal reheat operation, the nozzle actuating rams 26 are controlled by a piston 80 slidable in a cylinder 81 and subjected on side 81A to the compressor outlet pressure P 3  and on the other side 81B to the jet pipe pressure P 6  respectively communicated through lines 82 and 85. The stem 75 of piston 80 slides within a sleeve carrying a slave piston 70 subjected on both sides 71A, 71B to high pressure fuel supplied through lines 72, 86. The piston 80 controls the leak-off of fuel from either side of piston 70 to line 78 such that should P 6  increase, for example, piston 80 moves to the left allowing fuel to leak from side 71A of piston 70 so that the latter moves to the left taking with it rod 59. The latter moves via links 57, 56, 55, 53 a spool valve 44 controlling the flow of high pressure fuel to the rams 26 causing each ram piston 30 to move to the right and increase the opening of the nozzle 35. A mechanical or hydraulic feedback 66 ultimately restores spool valve 44 to its central position. Pressure fuel line 86 communicates with an annular space 87 located within a cylinder 88 between the wall of the cylinder and a sleeve 61 axially slidable therein. The sleeve 61 has radial drillings 61A, 61B communicating respectively with an annular space 89 connected to a fuel supply line 90 and with the space 87. A rod 91 is mounted for axial sliding movement within sleeve 61 under the control of the manually operable pilot's lever 92. The rod 91 has an axial passage 93 communicating with a cylinder 94 having a drain 95 and with a radial drilling 97. In the relative positions of sleeve 61 and rod 91 shown, a reduced diameter portion 98 of the rod connects drillings 61A, 61B so that any high pressure fuel supplied to the line 90 may pass via the drillings and annular spaces to the line 86 so as to render the slave piston 70 operative, i.e. positionable by the piston 80. However, should parts 61, 91 be displaced in either direction relative to each other from the position shown, then fuel will be prevented from flowing to line 86 and the slave piston will be rendered inoperative. The sleeve 61 carries a servopiston 99 slidable in a cylinder 100 and provided on both sides with high pressure fuel through lines 114, 115, 116. Radial drillings 101, 102, in the sleeve on respective sides of piston 99 permit fuel leak-off to drain 95 when a drilling 101 or 102 communicates with the drilling 97 in rod 91. In the position shown no fuel is being supplied to the reheat burners and slave piston 70 is inoperative since communication between supply lines 90 and 140 is closed off by an axially slidable valve member 121. However an annular recess 125 in slide 121 permits fuel to flow through lines 141, 142 to fill a reservoir 143 by urging a charging piston 147 to the right against a spring 150. Fuel is prevented from leaving the reservoir 143 since outlet line 146 is closed off by slide 121. When reheat is selected by moving pilot's lever 92 clockwise, rod 91 moves to the left allowing fuel to leak-off from the left side of piston 99 so that the piston also moves to the left taking with it sleeve 61. The latter moves links 53 and 62 to respectively operate spool valve 44 to open the nozzle 35 and to cause unit 23 to supply fuel to the reheat burners. Simultaneously a pinion 123 connected to lever 92 and engaging a rack 122 on slide 121 moves the slide to the right to the position illustrated in Fig. 3 (not shown) in which lines 140, 90 connect via recess 124 and lines 141, 142 to the reservoir 143 are placed out of communication. At this stage the relative positions of slide 61 and rod 91 prevent communication between lines 90, 86 so that control of the nozzle area by slave piston 70 is over-ridden and the control is entirely by lever 92. Piston 99 continues to move to the left until a drilling 103 in the piston aligns with a port 106 permitting fuel from the right side of the piston to flow to drain through a line 105 via an open slide valve 107. Thus further increase in the nozzle opening or the reheat fuel supply is temporarily prevented irrespective of the position of lever 92. The simultaneous movement of slide 121 also places outlet line 146 from reservoir 143 in communication via recess 126 with a line 151 leading back to a different part of cylinder 145. A recess 160 is so positioned in the piston 147 that as the piston moves to the left under the action of spring 150 the fuel discharging from reservoir 143 first flows to line 153 and past non- return valves 157, 158 to respectively prime the pilot and main reheat burners 22, 21 and then a fraction of a second later flows via lines 155, 24 to the hot streak igniter 25. When piston 147 nears its full leftward travel a tappet 163 on the piston engages a tappet 112 to close slide valve 107 and shut off drain 105. Thus piston 99 can now continue its leftwards movement to further increase the nozzle area and reheat fuel supply until the setting determined by lever 92 is reached. At this point slide 61 and rod 91 once again have the relative positions shown so that fuel can flow from line 90 to line 86 and the slave piston 70 resumes control of the nozzle area. In this embodiment the period in which the slave piston 70 is inoperative after selection of reheat by lever 92 is 3 seconds. The linkage 53, 55 &c. is arranged so that during this period the nozzle area selected by the lever 92 is 10% greater than that which would result from automatic control by the pistons 70, 80. A tapered needle 84 carried by piston 80 and cooperating with a leak-off 83 from chamber 81A of cylinder 81 assists the piston 80 to move rapidly to the left with any increase in jet pipe pressure P 6 , e.g. when reheat is initiated.