Patent GB-806210-A (GB)
Title: Fuel supply systems for ram jet power units of aircraft
Inventor: COOPER PETER JOHN
IPC: F02K7/10
Filed: 1956-04-23
Abstract: 806,210. Jet propulsion plant. NAPIER & SON Ltd., D. April 8, 1957 [April 23, 1956], No. 12424/56. Class 110 (3). [Also in Group XXIX] A fuel supply system for a ram jet comprises means for delivering fuel through a metering orifice to a burner in the ram jet, a fuel supply regulator which maintains the pressure drop across the metering orifice at a constant value, a device sensitive to Pitot pressure for adjusting the size of the metering orifice and hence the fuel flow as a function of the Pitot pressure and a flight Mach number sensing unit which operates at a predetermined Mach number to increase the size of the metering orifice independently of the orifice adjusting device so that the function relating fuel flow to Pitot pressure is automatically changed when this Mach number is attained. Fuel is supplied to a number of ram jets arranged along the wing of an aircraft by a pair of centrifugal fuel pumps driven by an air turbine. The discharge pressure of these pumps is maintained constant by throttling the air turbine exhaust. The fuel then passes through a metering pressure drop regulator 23, Fig. 2, and a metering unit 33, Fig. 3, to the burners of the ram jets. The fuel enters the pressure drop regulator at the volute 24 and passes through the ports 26, 29 to the discharge pipes 31, 32. The area of flow through the ports 26, 29 is controlled by the piston 27. The pressure in the discharge pipes 31, 32 acts on the underside of the piston and a spring 38 and the pressure on the discharge side of the metering unit on the top side of the piston. The piston 27 is in equilibrium when the pressure drop across the metering unit equals the loading of the spring 38. The loading of the spring 38 can be reduced by operation of the pilot's control 35. In its normal position a movable abutment piston 40 is held against a fixed stop 41 by fluid pressure in the chamber 42. Operation of the control 35 reduces the loading of the spring 47 which allows the valve 43 to rise and fluid to escape from the chamber 42. The piston 40 rises until equilibrium is re-established. The metering unit 33, Fig. 3, comprises a ported inner sleeve 50 slidable within an upper outer sleeve 51 and a lower outer sleeve 52. The ends of the outer sleeves are separated by a gap 53 the length of which can be altered by longitudinal movement of the lower outer sleeve 52. The area of the metering orifice 34 is determined by the position of the inner sleeve 50 relative to the gap 53 and the size of the gap. The inner sleeve 50 is moved by a servomotor 61. The control valve 62 of the servomotor is controlled by an evacuated capsule 63 enclosed in a chamber 64 subject to Pitot pressure through a pipe 65 containing a Mach number sensing unit of known construction. Up to a predetermined Mach number, say 3.0, the capsule 63 changes length and operates the control valve 62 to position the inner sleeve 50. The lower sleeve 52 is movable in response to another flight Mach number sensing unit which is also of known construction and controls a valve in a pipe 76. When a predetermined Mach number is reached, say 1.1 fluid is admitted to above the piston 77 and the sleeve 52 drawn downwardly a predetermined amount. The arrangement is such that up to a first predetermined Mach number (say 1.1) the fuel flow is controlled in accordance with a particular function of the Pitot pressure. Above this Mach number the fuel flow is controlled in accordance with another function of the Pitot pressure until a second predetermined Mach number is reached. At this point the second Mach number sensing unit opens a bleed-off valve in the pipe 65 so that the pressure to which the capsule 63 is exposed is falsified and in less than the Pitot pressure. The fuel supply is thereby reduced. The control 35 may be used by the pilot to reduce but not increase the fuel flow set by the automatic system.