GB847286A - Improvements in or relating to air intakes - Google Patents

Abstract

847,286. Jet-propulsion plant. HOBSON Ltd., H. M. Oct. 14, 1958 [Dec. 17, 1957], No. 39205/57. Class 110 (3). [Also in Group XXIX] A supersonic air intake 10 includes a lip 13 and a centre body 11 situated opposite the lip and defining with the latter the entry to the air intake, an oblique shock wave A being formed when air at supersonic speed enters the air intake. A pressure-sensing probe 18 is located just outside the lip of the air intake and a device responsive to changes in the pressure ratio Pr/Ppo is provided for adjusting the shape of the centre body 11 so as to maintain, throughout a given range of Mach number the oblique shock wave on the lip of the air intake, Ppo being the pressure sensed by the probe 18 and Pr being the ram pressure at a point 19 in advance of the centre body. The pressureresponsive device may comprise a microjet 30 as shown in Fig. 3a, which comprises a flexible diaphragm 23 carrying a rod 32, the upper side of the diaphragm being subjected to pressure Pr and the lower side to pressure KPpo which is a predetermined proportion of the signal pressure Ppo. This latter pressure is applied through a pre-set inlet orifice 24 of an air potentiometer, the outlet orifice 25 being of variable area dependent on the position of a tapered needle 26 mounted on the rod 32 attached to the diaphragm. The rod 32 serves to actuate the relay valve of the hydraulic actuator 12 which varies the shape of the centre body 11. The microjet device acts on the pilot valve of an hydraulic servo mechanism. The inlet or outlet of the microjet may be modified in dependence on a Mach number signal. Thus in Fig. 3b, a second microjet 27, modified to operate as a Mach number sensor, is arranged to vary in response to changes in Mach number and by means of a needle 31 to vary the size of the inlet orifice 24 to the main microjet 30. The pressures Pr and P po are applied to the microjet 30 as in Fig. 3a. Pressures Pm and Po are applied to the Mach number sensor 27, Pm. and Po being the total and static pressures respectively picked up by a Mach number probe. The sensor 27 comprises two diaphragms 28, 29 of different areas, the pressures being applied as indicated. In the arrangement shown in Fig. 3c, the position of the piston 33 of the hydraulic actuator 12 is taken as a measure of Mach number. Movement of the piston 33 varies the size of the inlet orifice 24 to the main microjet 30 by means of a needle 34 actuated by a cam 35, the position of which is controlled by piston 33. In a similar arrangement, the area of the outlet orifice 25 of the main microjet 30 is controlled in dependence on the position of the hydraulic actuator 12 and of the associated relay valve 36. In the case of the normal shock wave B, a sensor operating at all Mach numbers on a pressure ratio approximating to unity could give the desired result. A microjet 130, Fig. 4, having three diaphragms 23A, 23B, 23C is provided. The pressure P pn sensed by the probe 20 disposed just inside the lip 13 is applied between diaphragms 23A, 23B. The static pressure Ps sensed by the probe 21 on the centre body 11 is applied to the top of the diaphragm 23C. The servo pressure Psp sensed by the probe 22 located inside the air intake is applied between the diaphragms 23B, 23C and the pressure KPsp is applied to the lower side of the diaphragm 23A. The rod 32 is connected to the relay valve 37 of the actuator 14 which controls a valve 15 for spilling air from the air intake.