GB759783A - Improvements in or relating to gas-turbine engines driving variable-pitch propellers - Google Patents

Abstract

759,783. Gas turbine plant; axial-flow compressors. ROLLS-ROYCE, Ltd. Dec. 17, 1954 [Dec. 22, 1953], No. 35671/53. Classes 110(1) and 110(3) [Also in Group XXXIII] In a propeller-driving compound gas turbine engine comprising a high-pressure compressor 2 driven by a high-pressure turbine 14a, a low-pressure compressor 1 driven by a low-pressure turbine 15a, and a propeller 18 driven by the low-pressure turbine and having a unit 20 to vary the pitch of the propeller blades 18a in a manner to maintain the propeller at a selected speed which increases as the actual speed of the high-pressure compressor rotor increases, the pitch change is effected by a hydraulic motor 21 controlled by a valve 22 operated by a governor 23 and loaded by a spring 37 and a flexible diaphragm 38 subjected to fluid pressure. A pump 24 delivering oil from a tank 25 into a pressure line 26 leading to the engine lubricating system supplies oil to a pump 28 which delivers into a high pressure line 29. A branch 42 of the main pressure line 26 supplies a pump 43 driven at a speed proportional to that of the high-pressure rotor through a shaft 44. The pump delivers to conduits 45, 46 having flow restrictors 47, 48, 49. The chamber 39 on the low-pressure side of the diaphragm 38 is connected to the main pressure line 26 through pipe 40 and the high-pressure chamber 41 is connected by a pipe 60 to a valve box 61 having a valve-controlled inlet 62 connected by a pipe 63 to conduit 45, hence when the inlet 62 is open the pressure in chamber 41 is controlled so that the speed of the lowpressure rotor is maintained in a desired relation to the speed of the high-pressure rotor. A conduit 64 connects a branch 33 of the high pressure line 29 with the main pressure line 26 and has in it flow restrictors 65, 66, 67, the downstream pipe 75 being common to conduits 45 and 64. A bleed line 71 contains a relief valve 72. A pressure connection 73 is taken from conduit 64 to an inlet 74 in the valve box 61. The inlets 62, 74 are controlled by elements 76, 77 on a pivoted lever 78 connected to the valve member 79 of a bleed valve 3 at the outlet of the low-pressure compressor 1 so that when the bleed valve is open the inlet 74 is open . A capsule 68 varies the area of the restrictor 66 in accordance with the temperature at the intake to the low-pressure compressor so that the load on the diaphragm 38 also depends on this temperature and hence selected corrected rotational speed of the low-pressure rotor will be maintained during landing. The lever 78 is connected to a two-position ram 80 movable from one position to the other by the pilot so that the bleed valve is open during landing. The ram has a spring-loaded differential area piston 81, both sides of which are connected to the fuel supply line, fuel being supplied from a tank 6 through a booster pump 11, low pressure shut off cock 12, pump 8, control 9, and high pressure shut off cock 13 to burners 5. Pressure space 83 on the larger area side of the piston has an outlet 86 controlled by a solenoid operated valve 87. A capsule 50 varies the area of the restrictor 49 in accordance with the temperature at the inlet to the high-pressure compressor, and the pressure drop across the restrictor is applied across a diaphragm 90 by means of pipes 91, 92 so that during landing the speed of the high-pressure rotor is maintained above the selected minimum value automatically, i.e. when the pressure drop falls below the value corresponding to the minimum permissible corrected speed the spring 93 closes a valve 94 controlling outflow from a cylinder 95 fed from a pressure source 96 so that a piston 98 moves to increase the fuel flow to the main combustion equipment 4 by its action on the pump 8 or control 9. In the event of a baulked landing the pilot moves control 9 to increase the speed of the high-pressure rotor and automatcially actuates a switch 100 to energize the solenoid operated valve to move piston 81 and thereby close the bleed valve 3 to allow the speed of the low-pressure compressor to be controlled in accordance with the speed of the highpressure compressor, thus permitting rapid acceleration without surging. On touchdown, if it is desired to close the bleed valve 3 to restore the low-pressure rotor control to follow the high-pressure rotor speed, this may be effected by closing a switch 101.