Patent GB-766833-A (GB)
Title: Improvements in and relating to automatic control of aircraft power plants
IPC: F02K7/10
Filed: 1954-07-15
Abstract: 766,833. Jet propulsion plant. LEDUC, R. July 15, 1954 [July 15, 1953], No. 20712/54. Class 110 (3). [Also in Groups XIX, XXIX and XXXII] This invention relates to improvements in the thrust regulating means for an aircraft power plant claimed in Specification 663,952. These improvements consist in (a) providing in the case of an aircraft powered by a thermopropulsive duct automatically operating means for ensuring that the " maximum heating " temperature of the combustion chamber, i.e. the temperature at which the thrust attains its optimum value is not exceeded despite rough handling of the pilot's control; (b) providing means to compensate for the intrinsic elasticity of the capsules or bellows used in the apparatus; and (c) providing manually controlled means for varying the leverage exerted by the aneroid capsules 1, 2 responsive respectively to the ambient static pressure Po and the total ram pressure Pt such that the bellows or capsules may be balanced dynamically in all positions. In Fig. 1, the aneroid capsules 1, 2 are connected to a lever 5, the fulcrum 6 of which is adjusted by a manual control member 7 as in Specification 663,952. The projecting end of the lever 5 is linked to a floating lever 9 connected to a piston valve 10 controlling a servo-piston 18 and also to a rod 21 the lower end of which bears a roller 20 engaging a cam 19 operated by the piston 18. The piston 18 adjusts a fuel admission valve (not shown) and so regulates the power plant as to keep the Mach number corresponding to the aircraft's true air speed at a predetermined value selected by the pilot. The cam 19 and rod 21 operate on the lever 9 as a follow-up control to reset the valve 10. If overheating occurs due to incorrect handling of 'the manual control 7, control of the servopiston 18 by the valve 10 is prevented by a further piston valve 29 in series with the valve 10. The valve 29 is operated by a lever 26 subject to the opposed actions of two further capsules 22, 23. The capsule 22 is responsive to the difference between total ram pressure Pt and ambient static pressure Po and the capsule 23 is responsive to the difference between total ram pressure Pt and the static pressure P1 at the entrance to the thermopropulsive duct. The ratio Pt-Po/Pt-P1 rises with the combustion chamber temperature and has a determinate valve at the so-called " maximum heating " temperature corresponding to optimum thrust. The position of the fulcrum 27 of the lever 26 is chosen so that at the determinate value of the ratio the lever 26 is balanced in the position shown and the valve 29 does not interfere with the control of the servo-piston 18 by the valve 10. If overheating occurs the valve 29 is depressed so that the piston 18 is hydraulically locked in its adjusted position. If the combustion chamber temperature continues to rise, the valve 29 will be depressed further so as to connect the right-hand end of the piston 18 to exhaust and so reduce the fuel supply. Fig. 2 shows an arrangement for compensating for the intrinsic elasticity of a capsule 37 in a rigid casing 45 to which the lower end of the capsule is anchored by a stem 51. The upper end of the capsule carries a stem 38 to which is pinned a sleeve 39 having a flange 46 engaged by two levers 49, 50 arranged synimetrically with their axes 43, 41 parallel but at right angles to the stem 38. The outer ends of the levers are connected by a pair of tension springs 44, the unstretched length of which is equal to the distance 2a between the axes 41, 43. The springs 44 are also chosen so that the ratio of the force required to compress the capsule through a given length to the force required to stretch the springs an equal length is 4n<SP>2</SP> where n is the ratio of the length of the outer arm n1 of one of the levers 49, 50 to the inner arm 1. This arrangement may be applied to any or all of the capsules 1, 2, 22, 23. In Fig. 3, the rapsules 1, 2 of Fig. 1 are arranged in casings 5, 55, 54. The free end of the capsule 2 has a stem 56 pivoted at 4 to a lever 57 connected at 8 to the floating lever 9. The stem 62 of the capsule 1 is pivoted to a straight lever 59 having a pivot 60 fixed with respect to the casing 55. The casing 55 may be turned by a hand-operated lever 61 so that the end of the lever 59 engages the lever 57 at an adjustable point 6 whereby the leverage exerted by the capsule 1 on the lever 57 is varied. It is shown in the Specification that the ratio Po/Pt is proportional y/x where x and y are the distances of the pivots 58, 60 respectively from the adjustable point of contact 6. As there is no rigid connection between the moving parts associated with the respective capsules each may be independently balanced dynamically.