Patent GB-634417-A (GB)
Title: Improvements in or relating to control systems for gas turbine propeller engines
IPC: F02C9/16
Filed: 1947-07-30
Abstract: 634,417. Fluid-pressure servomotor-control systems. BENDIX AVIATION CORPORATION. July 30, 1947, No. 20654. Convention date, Sept. 12, 1946. [Class 135] [Also in Group XXVI] A control system for a gas turbine power plant driving a variable pitch propeller comprises a fuel conduit with a variable metering restriction the area of which is controlled by an element which is connected together with the means for varying the pitch of the propeller blades to a power control member. Fuel is supplied by a pump 33 through a pipe 97 to a gas turbine driving a variable pitch propeller 25. The flow of fuel is controlled by two variable area orifices 53, 54 regulated by two needle valves 55, 60. After starting, the engine is accelerated by moving the manual lever 561 to the right to increase the fuel flow through the orifice 53. When the stop 66 is reached the spring loaded latch member 71 enters the notch 74 of the member 56 and withdraws from the notch 75 of the member 61. This allows the power control lever 61<SP>1</SP> to be moved to the right and to further increase the fuel supply by opening the orifice 54. At the same time a cam 115 of the member 61 acting through a bell crank 113 and levers 112, 110 compresses the governor spring 109 of an engine driven governor 103 which controls through a valve 27 the flow of pressure fluid to the pitchchanging mechanism 104 of the propeller 25. Compression of the spring 109 causes the governor weights 103<SP>1</SP> to move inwards and operate valve 27 to allow pressure fluid to flow to the mechanism 104 and change the propeller blade angle so that the turbine speeds up. The governor weights 103<SP>1</SP> then move outwards and shut off the supply of pressure fluid. To prevent operation of the valve 27 during periods of acceleration and deceleration, an inertia wheel or flywheel 131 is driven by the engine through gearing 106, 107<SP>1</SP>. The flywheel is mounted on a worm 130 forming part of the driving shaft 107. Contact rollers 141, 142 mounted on one of the arms of the bell cranks 134, 135 lie adjacent the wheel 131 whilst the opposite arms of the cranks are adapted to be engaged by contact member 143 on the stem 108 of the valve 27. When accelerating or decelerating the wheel 131 moves up or down the worm 130 and contacts one of the rollers 141, 142 and thereby prevents movement of the valve 27 in one direction or the other. A torsion spring 144 re-centres the wheel 131 when the engine is running normally. When it is desired to run the engine at maximum speed but with a low pitch on the propeller blades, the lever 126 is pushed to the right, this causes the plunger 121 to contact one arm of the bell crank 113 and thus override the action of the cam 115. The lever 124 operated by the lever 126 is also provided with an offset extension 128 which engages a lug 129 on the member 61 to ensure a minimum opening of the valve 60. The pressure drop between the fuel pump discharge and the inlet to the burners is maintained constant by a balanced valve 35 controlled by a diaphragm 40 movements of which are dependent upon these two pressures. The pressure drop across the metering orifices 53, 54 is maintained substantially constant by a regulator unit R controlling a balanced valve 46. The unit R operates in response to changes of pressure between the chambers D and C. The chamber C is connected to the discharge side of the orifices 53, 54 through a chamber E and a fixed orifice 80. To compensate for changes of altitude a barometric capsule 76 is provided to control a needle valve 77 which varies the size of the orifice 78, between the chambers D and C. As the pressure drop between these chambers is maintained constant by the unit R, the flow through the chamber C will be proportional to the area of the orifice 78. The pressure drop across the orifice 80 is proportional to the flow so that the pressure drop between the chambers D and E will be proportional to the area of the orifice 78 and thus vary with altitude. A balanced valve 81 operated by a diaphragm 84 is used to prevent overspeeding. The chamber 85 on one side of the diaphragm is connected to the discharge of an engine drive centrifugal impeller 88.