Patent GB-932751-A (GB)
Title: Improvements in air intakes
Inventor: LANE RAYMOND JOHN
IPC: F02C7/042
Filed: 1958-09-01
Abstract: 932,751. Jet propulsion plant. BRISTOL SIDDELEY ENGINES Ltd. Aug. 27, 1959 [Sept. 1, 1958], No. 28067/58. Class 110 (3). [Also in Group XXXIII] An air intake for a power plant comprises a first boundary member and a secondary boundary member forming opposite sides of an intake passage extending through a throat to a diffuser, the first boundary member having upstream of the throat, a leading edge and a flank which faces towards the passage and extends to the throat and the secondary boundary member including a flat lip which extends from its upstream end to the throat and forms with the flank, when the flank and lip are in normal positions, a convergent entry passage to the throat; the flank being articulated to the remainder of the intake for relative tilting from its normal position to increase the size of the throat and the lip being articulated to the remainder of the intake for relative tilting from its normal position to a position in which it defines with the flank a non-convergent entry passage. The intake, which may be used to supply air to power plant of the kind described in Specifications 894,716 and 894,822, is rectangular in cross-section and comprises a passage having a throat 3 and a divergence between walls 4, 5. The upstream end of the wall 4 is defined by a wedge member 6. The flank 7 of the wedge member 6 turned away from the passage is flat and, at the designed Mach number is substantially in alignment with the direction of the relative airstream 2 and with the upper surface 8 of the body. The flank 9 is oblique to the direction 2 and constitutes a curved compression surface. The wall 5 has a lip 10 at its upstream end, is flat and at the designed Mach number in alignment with the direction 2. The position of the lip 10 and obliquity of the flank 9 are so chosen that, at the designed mach number an oblique shock wave 11 extending from the tip of the wedge touches the lip 10 and iso-Mach number lines 13 originating from points on the surface 9 converge to positions along the wall 5 from the lip 10 to the throat 3. At the designed Mach number, the band of air intercepted between the lips 10, 12 is compressed by passage over the surface 9 so that it passes wholly between the lip 10 and the opposed part of the compression surface. As the Mach number is reduced, the oblique shock wave 11 and the iso-Mach number lines 13 spread to make increasing acute angles with the direction 2 and the amount of compression of the air flowing over the surface 9 is reduced. Consequently the whole of the deflected air cannot enter the space between the lip and the opposed part of the compression surface and the lip 10 is at a substantial angle of incidence to the air flowing past it. These conditions lead to excessive drag. To eliminate these defects the compression surface 9 and throat forming part 14 are formed on a wedge 6 which is articulated to the structure 4, 5 so that it can move in a manner which approximates to rotation about an axis 15. The forward part 16 of the upper wall 4 is hinged at 17 to follow the movements of the part 14. By tilting the member 6, the area of the throat 3 is increased and the part of the compression surface 9 opposite the lip 10 becomes more nearly aligned with the direction of the lip. These features reduce the drag. To improve performance under intermediate and take-off conditions, the lip 10 is formed on a forward portion 20, Fig. 4, of the wall 5 which is hinged at 21. The movements of the portion 20 are interrelated with the movements of the member 6 through a cam 22, a cam follower 23, bellcrank 24 and link 25. The member 6 may be actuated by a servomotor in response to signals from a Mach meter as described in Specification 896,982. Openings 26 may be provided for drawing off the boundary layer.