Patent GB-603780-A (GB)
Title: Improvements relating to propulsive systems for aircraft
IPC: B64D27/16
Filed: 1944-02-10
Abstract: 603,780. Fluid-pressure servomotor-control systems. POWER JETS, Ltd., and McLEOD, R. C. Feb. 10, 1944, No. 2518. [Class 135] [Also in Group XXVI] In a jet propulsive system for aircraft comprising a gas turbine prime mover in which thrust augmentation is provided by the burning of secondary fuel in the exhaust from the prime mover or in an airflow promoted by an airscrew, blower, injector or the like energized by the prime mover, the means controlling the flow of secondary fuel is operated by differential transmission mechanism, one part of which moves in response to a flow characteristic of the secondary air stream and the other part of which moves in response to the speed of the rotary means producing the secondary air stream. As shown, a gas turbine 2, Fig. 1, drives a compressor 1 supplying air to combustion chambers 15 supplied with fuel by a pump 99 through piping 100. The products of combustion after driving the turbine 2 pass through an annular duct 10 to constitute the main propulsion stream, but before leaving the duct 10 they drive the gas turbine element 81 of an augmenter unit 79 carrying also a further compressor or ducted fan 80 which entrains secondary air in an annular duct 11. Secondary fuel supplied by a pump 4 through piping 6 is burned in the secondary air further down the duct 11 to constitute a secondary or augmenting propulsive stream when a particularly high thrust is required, e.g. at take-off or at altitude for operational reasons. The secondary fuel supply is controlled differentially by a spill-off valve 9 in accordance with the velocity of the secondary air and the rotational speed of the fan 80 producing the air flow. This is done by differential gearing 31 shown in detail in Fig. 3. A coarse pitch windmill or anemometer 8 in the duct 11 drives one of the bevel gears 30 of the differential gear through a pinion and crown wheel 22, 23, a shaft 24, spur gears 25, 26, a shaft 101 and bevel gears 28, 29. The augmenter unit 79 drives another bevel gear 35 in the differential gearing through gears 82, 83 (Fig. 1), a shaft 14, skew gearing 32, 33 and a second input shaft 47. To prevent the augmenter unit 79 driving the windmill 8, a friction clutch which may have cooling means, is arranged between the gear 33 and the shaft 47. A third bevel gear 36 of the differential gearing is carried on a cage 37 which rotates on a shaft 7 controlling the valve 9 through a gear 34, and a segmental rack 91 on the shaft 7. The valve assembly 9 is shown in detail in Fig. 5 and comprises a piston valve 65 controlling the connection between a pipe 61 leading from the piping 6 and a pipe 64 leading back to the main fuel tank. The valve 65 is directly-operated by a spring-loaded piston 56 exposed through a passage 59 to the pressure of a servo-fluid, e.g. fuel, under the control of a piston type pilot valve 93. The latter is operated from the shaft 7 through an arm 85, a link 51 and a floating lever 52 which is also coupled to the rod 55 connecting the valve 65 and the piston 56 and acts to restore the valve 93 to its neutral position. Fig. 7 shows a device 48 for varying the angle of incidence of the air on the blades of the windmill 8 located on the upstream side of the latter. It comprises a fixed ring 3 and movable rings 5, 6A between which stator blades 97 are mounted on pins 13. One end of each blade carries a pin 98 restrained in a slot in the fixed ring 3. The inclination of the blades 97 is adjusted by rotating the rings 5, 6 by a rack 69 and a pinion (not shown) operated by a control lever. Fig. 9 shows a modification in which the cage 20 of the differential gear drives the shaft 77 of the gear pump 4 supplying secondary fuel. The differential gear in this case comprises a sun-wheel 71 driven by the windmill 8 through spur gearing 22, 69, an annulus 73 driven by the augmentor through gears 74, 76 and shaft 14, and a planet gear 88 carried by the cage 20. Specification 583,111, [Group XXVI], is referred to.