Patent GB-797434-A (GB)
Title: Improvements in or relating to aircraft
Inventor: METCALFE THOMAS LAIDLER
IPC: B64D7/02
Filed: 1955-05-25
Abstract: 797,434. Gas turbine plant. ROLLS-ROYCE, Ltd. May 25, 1956 [May 25, 1955], No. 15153/55. Class 110 (3). [Also in Group XXIX] An aircraft fitted with a gas turbine jet propulsion engine and a gun or guns, in which there is a tendency for a compressor of the engine to surge when the guns are fired under certain conditions, has means for bleeding off air from the delivery of the compressor of the engine in which the tendency to surge is present which is automatically operated on firing of the guns. The invention is described with reference to a gas turbine jet propulsion engine having an axial-flow compressor supplying combustion air to combustion equipment feeding a turbine driving the compressor. The engine is fitted with bleed valves 20 at the compressor outlet by which compressed air is bled off to atmosphere. Each bleed valve comprises a stepped casing 21 enclosing a piston 25 which co-operates with a seating 22 at the outlet of a small diameter bore 23 in communication with the compressor outlet. The piston 25 is loaded in the opening direction by a light tension spring 28. The bleed valves are controlled by a common control valve 32 which comprises a chamber 33 having ports 34, 35 at either end which communicate with the compressor delivery pressure and the atmosphere respectively. The ports 34, 35 are controlled by a valve member comprising a rod 37 having flanges 38, 39 at either end. The valve member is controlled by a solenoid 46 acting through a half-ball valve 44. When the solenoid is de-energized, the valve 44 is opened by a spring 44A so that there is a flow from the compressor discharge through the passage 43 and around the loosely fitting flange 39 to atmosphere through the vent 42. This causes a pressure drop across the flange 39 which is sufficient to overcome the load of the spring 40 and so cause the valve member to close the port 35 leading to atmosphere and to open the port 34. Compressed air from the compressor delivery then acts on the pistons 25 to keep the bleed valves 20 closed. When the solenoid 46 is energized by pressing the gun firing button 48, the half-ball valve 44 is closed and the valve member is actuated by the spring 40 to close the port 34 and open the port 35. This vents the space 31 to atmosphere and causes the bleed valves 20 to open. To prevent overheating and surging of the engine when the bleed valves are opened the fuel supply is also temporarily reduced and when a top speed governor and acceleration control unit are fitted, the governor is set to govern at a lower speed and the accleration control unit isolated from the fuel control means. Fuel is supplied to the engine by an engine-driven swash-plate pump 50 controlled by a servo-piston 54. The position of the piston 54 is determined by the pressure in the space 58 which is controlled by a number of vent valves of which one 60 is associated with the top speed governor 61, another with the acceleration control unit 62 and a third (not shown) with a barometric control unit (not shown). The top speed governor comprises an impeller 63 which discharges to a space 64 on one side of a diaphragm 65. The space on the other side of the diaphragm is connected to the pump inlet pressure so that the pressure drop across the diaphragm is proportional to the engine speed. The diaphragm is also loaded by a tension spring 69 and controls through a pair of levers 71 the half-ball vent valves 60. One end of the spring 69 is secured to a piston 67 arranged to move between two limiting positions in a cylinder. To reduce the fuel supply when the guns are fired, a by-pass 79 having a solenoid actuated control valve 80 is provided. When the solenoid is de-energized, the half-ball valve 92 is in the closed position. The pressures on the opposite sides of the piston 81 are then equal so that the piston 81 is urged on to'the seating 82 by a spring 88 and no fuel flows through the by-pass. When the guns are fired, the solenoid 92A is energized and the flow through the restrictors 89, 90 resulting from the opening of the half-ball valve 92 will cause the pressure on the underside of the piston 81 to fall and the piston 81 to be moved off its seating. The firing of the guns will also cause the solenoids 102, 105 to be energized. The energization of the solenoid 105 will cause the half-ball valve 104 to be closed and prevent the acceleration control unit 62 from affecting the fuel pump 50. The acceleration control unit 62 is of the type described in Specification 651,599 which comprises essentially a pivoted lever carrying a half-ball vent valve which is loaded in the sense of opening the valve by a load proportional to the fuel flow to the engine and in the opposite sense by a load proportional to the compressor delivery pressure. Energization of the solenoid 102 closes the half-ball valve 100. This allows the pressure in the space 97 to rise and move the piston 67 to the left and lower the load on the spring 69 and so lower the speed at which the governor is set. If desired, a delay relay 106 may be provided to ensure that the guns do not fire until the fuel and air bleeds have come into operation. When the engine is of the compound type having independently rotating low-pressure and highpressure compressors driven by separate turbines, the bleed valve or valves may be located at the delivery of either compressor depending on which compressor tends to surge. In a modification of the solenoid actuated control valve 80, the restriction 85A is moved to a position downstream of the junction of the conduits 85, 91 and a non-return valve placed immediately downstream of the seating 82. Specifications 583,487, [Group XXIX], and 645,908, [Group XI], also are referred to.