GB920328A - Improvements relating to silencers for jet propulsion engines - Google Patents

Abstract

920,328. Jet propulsion nozzles. FAIREY CO. Ltd. Aug. 17, 1959 [Aug. 29, 1958], No. 27860/58. Class 110 (3). A jet propulsion nozzle silencer comprises an open-ended tubular shell having a number of generally longitudinally extending tubes let into its wall, the tubes being inwardly inclined to the axis of the shell from front to rear and leading in through apertures formed in the wall of the shell, the leading edge of each tube being cut away obliquely level with the exterior surface of the shell to form an elongated inlet aperture exposed to the atmosphere at or adjacent to its leading end, and each tube having a discharge aperture constituted by its rear end within the wall of the shell, the tubes being arranged in side by side relationship around the axis of the shell with their rear ends arranged in a ring with the rear end of the shell so as to define a discharge nozzle whose mouth has a central aperture of reduced crosssection. The invention is described with reference to a jet propulsion engine adapted to be mounted at the tips of the rotor blades of a helicopter. The silencer, Fig. 1, comprises a shell 10 having a series of elongated apertures 11 adapted to receive tubes 12 of generally cylindrical form, which extend obliquely through the apertures into the interior of the shell where they are grouped in side by side relationship around the axis of the shell to which axis each tube is slightly inclined inwardly in the direction from front to rear. The tubes 12 are riveted and welded at 15 to the rear end of the shell and are reinforced by horseshoe-shaped members 17. The radially inner portion of the rear end of each tube is deformed to form a troughed lip 18. The edges 19 of adjacent tube ends are spaced apart to define a generally star-shaped nozzle mouth having a small central aperture 22 and radial slots 23, each leading to a minor discharge aperture 24. Stiffening ribs 29 are formed on the shell 10 between the apertures 11. The tubes 12 are spaced apart along their whole length to form passages leading to apertures 24. The interior of the nozzle formed by the main central discharge passage 30 and the auxiliary passages is lined by an air-cooled liner 33 shaped to conform to the interior of the silencer. A narrow space 35 about one-tenth of an inch in minimum width is maintained between the surface of the liner and the surfaces of the tubes 12 and shell 10. The downstream edge of the line 33 stops well short of the downstream ends of three of the tubes 12 but extends practically as far as the extreme edges of the lips 18 of the remaining four tubes 12, which tubes need additional cooling due to the proximity of the spar of the rotor on which the engine is mounted. Compressed air from the combustion air supply to the combustion chamber is led into the space 35 through ports 47. The liner 33 may be perforated. The diameter of the central aperture 22 is preferably between one-tenth and onetwentieth of the total discharge area of the silencer as described in Specification 885,713.