GB878400A - Improvements in or relating to supersonic aircraft - Google Patents

Abstract

878,400. Fluid-pressure servomotor-control systems. ROLLS-ROYCE Ltd., and ENGLISH ELECTRIC CO. Ltd. Dec. 10, 1959 [Dec. 22, 1958; Feb. 27, 1959], Nos. 41392/58 and 7032/59. Class 135. [Also in Group XXVI] An air intake for a ram jet or a gas-turbine jet-propulsion engine for aircraft capable of supersonic flight at high Mach numbers has a variable geometry and is automatically controlled in the range of high supersonic Mach numbers by an inverted Pitot head having an orifice facing downstream and arranged close to the intake lip sensing the position of the normal shock wave and adjusting a part of the intake structure which affects the position of the normal shock wave so as to keep the wave in the optimum position at or immediately ahead of the intake lip. The air intake shown has a lip 1, a throat 2 with adjoining diffuser passage 3 and an adjustable double ramp 5, 6 pivotally mounted on the fuselage 15 and operated by an hydraulic jack 10. The forward ram 5 has a sharp leading edge 4 from which at high Mach numbers a first oblique shock wave originates which is directed closely ahead of the lip 1, adjacent to which is arranged an inverted Pitot head 7. A static pressure pick-up point 8 is provided on the forward ramp 5 behind the leading edge 4 and is connected to the underside of the diaphragm of a capsule 13, the upper side of which is connected to the Pitot head 7. The diaphragm of the capsule 13 is linked to the control valve 11 of the jack 10 which controls the throat area. An ordinary facing Pitot head is connected by a pipe 17 to the capsule 18 of a Mach motor comprising a bellows 19 and an evacuated capsule 22 which provides an absolute reference pressure. The Mach motor is connected by linkage 21 to a slotted cam 14 which is slidable only from right to left. The cam 14 has a curved narrow portion 14<SP>1</SP>, followed by a straight narrow portion 14<SP>11</SP> and by an enlarged portion 14<SP>111</SP>. A cam follower roller 114 of a diameter corresponding to that of the portions 141, 14<SP>11</SP> is journalled on a lever 20 pivoted at one end to a fixed point and at the other end to a floating lever 12. The lever 12 is pivoted at one end to the control valve 11 and at the other end to a rod 9 connected to the ramp 5 which forms a feed back from the ramps to the jack 10. The limits imposed by the portion 14<SP>111</SP> are such that control of the ramp 5 is not allowed to cause the oblique shock to be detached from the point 4. Downstream in the air intake duct overflow-valve 16 is provided so that if the ramps 5, 6 lie retracted to such an extent that the air pressure in the duct 3 would force the normal shock wave forward of the static pick-up point 8, the air pressure is reduced by the valve 16 opening. The door 16 may be secured by a spring-loaded latch operated by remote control from the pilot's cockpit or automatically, in response to air pressure at high supersonic speed. The arrangement is such that at take-off and low subsonic speed the ramps are controlled in accordance with Mach number. At transonic and low Mach number supersonic speed, the ramp angle is kept constant and at high supersonic speed the ramp angle is controlled so as to maintain the normal shock wave aft of the Pitot head 7. In a modification, Fig. 2 (not shown), a double inverted Pitot head is provided and the shock wave is maintained between the Pitot heads. A spring- loaded latch is also provided to lock the ramps 5, 6 in a low angle position at low speeds. The latch may be connected to a valve connecting the two ends of the jack with one another so as ti disable the jack. In a further modification, Fig. 4 (not shown), having two inverted Pitot heads, the operating diaphragms are arranged so that when the jack 10 pushes the ramps 5, 6 against the air load on them, the control valve is opened wider than when the ramps 5, 6 move in the same direction as the load. In another modification, Fig. 5 (not shown), the ramps 5, 6 are controlled by a piston the pressures on the opposite sides of which are controlled by half-ball valves carried by diaphragms responsive to the differences in pressure between two inverted Pitot heads and the static pressure at the point 8. In an alternative system four inverted Pitot heads are provided. The arrangement is such that if the shock wave is downstream of all the Pitot heads, the ram piston will move to rapidly increase the intake area; if the shock wave is downstream of the two intermediate Pitot heads but upstream of the downstream Pitot head, the piston will move slowly to increase the intake area. When the shock wave is between the intermediate Pitot heads the piston will be locked. If the shock wave is upstream of the intermediate Pitot heads but downstream of the upstream Pitot tube, the piston will move slowly to decrease the intake area and if the shock wave is upstream of the Pitot heads, the piston will move rapidly to decrease the area.