731,524. Jet propulsion plant. POWER JETS (RESEARCH & DEVELOPMENT), Ltd., and NAPIER & SON, Ltd., D. Jan. 17, 1952 [Jan. 17, 1951], No. 1342/51. Class 110 (3). [Also in Group XXIX] A combustion control system for an aircraft jet-propulsion plant, e.g. a ram jet device, controls the fuel supply during flight according to the expression Af(P 1 )#P 2 CP 1 , where P 1 is the static ambient atmospheric pressure, P 2 is a pressure, e.g. Pitot pressure, dependent upon the speed of flight, f(P 1 ) is a desired function of P 1 , and A and C are constants. An over-riding control regulates the fuel supply during initial flight conditions, e.g. during launching. Also, above a certain altitude means becomes operative for limiting the Mach number attained by the aircraft. A simplified representation of certain essential features of the invention is shown in Fig. 3, in which a member 13 ported at 13a to coact with an annular port 10a to form a metering orifice 10b is actuated through a lever 18 by an evacuated capsule 15 subject to static pressure P 1 . The port 13a is so shaped that the are of the metering orifice varies according to the desired function f(P 1 ) of P 1 . The pressure difference across the metering orifice is controlled by a regulating valve 2 upstream of the orifice and connected therewith by a conduit 5. The valve 2 is actuated by a diaphragm 7 subject to the pressure difference across the metering orifice and to the force of a spring 8 having a movable abutment 20 which is adjusted, through a lever 24, link 23 and floating lever 22, by the capsule 15 and by a capsule 21 subject to Pitot pressure P 2 . By this means the pressure difference across the metering orifice is controlled according to the expression (P 2 - CP 1 ) and the rate of flow of fuel varies as Af(P 1 )#P 2 - CP 1 . In the full system shown in Figs. 1, 2, fuel is delivered by a pump 57 driven by an air turbine 58 to the regulating valve 2 and thence through a conduit 5 and a device 76 to conduits 5b, 5c leading to metering orifices 10, 75. In the event of excessive fuel pressure being generated by the pump 57 a spring-loaded valve 59 is opened to admit fuel to a spring-loaded servo-piston 63 which throttles the exhaust from the air turbine. The regulating valve 2 is operated by a servopiston 2a controlled by a piston valve 28 having a connection through a lever 29 with the diaphragm 7 which is connected by a conduit 90, 5e with the pressure upstream of the metering orifice and by a conduit 9 with the downstream pressure. The metering orifice 10 is adjusted by the capsule 15 subject to static pressure and acting through a servo-device 34 with moving-seat follow-up. The metering orifice 75 is adjusted simultaneously through a lever 55 pivoting about a connection to a servopiston 54. As in Fig. 3 the spring abutment 20 is adjusted by the capsule 15 through the lever 24 which has an adjustable fulcrum 25, link 23 and floating lever 22. The latter is also actuated by a servo-piston 46 controlled by a piston valve 42 which is connected by a lever 40 with a diaphragm 38 subject on its upper face to Pitot pressure P 2 and on its lower face to static pressure P 1 . The means 51 for limiting the Mach number attained by the aircraft is subject to the pressures P 1 and P 2 and operates the metering orifice 75 in the closing direction through the servo-piston 54 when a certain Mach number is exceeded. To prevent operation of the means 51 below a predetermined altitude it is connected to the Pitot pressure through conduits 72a and 101 having a restriction 72 and a leakage path 72b controlled by a piston 69. The piston 69 is spring-urged to vent the passage 72b so that the Pitot pressure is not communicated to the means 51. However, at a particular altitude, an abutment 37 moved by the servo-device 34 engages an extension of the piston 69 and depresses it,to such extent that a pressure liquid port in the wall of the cylinder in which the piston 69 operates is exposed 'by the piston, whereupon the latter is fully depressed by the liquid pressure to close the passage 72b and render the means 51 operative. The device 76 operates to enable fuel to be supplied at aircraft speeds below normal, e.g. during, launching.. When the system is at rest a hollow piston 77 and a piston-valve 79 are urged by springs 78, 80 towards the left-hand end of a housing so that the valve 79 interrupts communication between a pressure conduit 4a and conduits 81 and 4c to relieve pressure on plungers 83, 88, 96, allowing them to be operated by loading springs 84, 89, 97 respectively. Thus, the plunger 83 increases the compression of the spring 8, the plunger 88 connects the conduit 90 to a conduit 5d instead of to the conduit 5e whereby the diaphragm 7 is subject to the pressure difference across -orifices 10, 76b in series, and the plungers 96 open ported piston valves 93 which distribute fuel to burner conduits 95 and are normally opened against springs 94 by fuel pressure. When the fuel pump is put into operation fuel leaks through an orifice 77b in the piston 77 causing the latter to move'gradually to the position shown and operate the valve 79. The opening 77a in the piston 77 is so shaped that the orifice 76b is initially fully open, but the first part of the movement of the piston causes the port to be restricted. Continued movement of the piston causes the port to be opened gradually.