GB818201A - Suppression of jet propulsion engine exhaust noise - Google Patents

Abstract

818,201. Jet propulsion nozzles. UNITED AIRCRAFT CORPORATION. May 27, 1957 [June 1, 1956], No. 16708/57. Class 110 (3). A jet propulsion engine comprises a tailpipe, an inner body substantially concentric with the tailpipe to form a gas passage, a plurality of hollow vanes each having a relatively large aperture in one side and a plurality of relatively small holes in another side and means to move the vanes between a clustered inoperative position in which they form a downstream continuation of the inner body and an outward operative position in which the large apertures are connected to the gas passage and the small holes discharge in a downstream direction. The exhaust gases from a gas turbine jet propulsion engine pass through a passage formed between the tailpipe 20 and an inner body 28 to atmosphere. The inner body 28 is axially movable and carries a number of fin-type vanes 22 which have a large single holes 24 in the forward edge and a plurality of small hole 26 in the trailing edge. When the vanes 22 are in the retracted position, top half of Fig. 2, they are clustered downstream of the inner body 28 to form a conical continuation of it. The exhaust gases then pass to atmosphere through the outlet 38. When noise suppression is desired, compressed air from the gas turbine compressor is supplied through the annular space between fixed members 48, 50 to the space 54. The pressure on the piston 56 causes the cylinder 58 and the inner body 28 to be moved forwardly to the position shown in the lower half of Fig. 2. This causes the vanes 22 to move about pivots 64 so that their inlet apertures 24 are connected to the exhaust gas passage. The exhaust gases are discharged to atmosphere through the small nozzles 26. Troughs 42, attached to or forming part of the tail pipe 20, are provided to block off the spaces between the hollow vanes 22 when they are in the operative position. Guide vanes 44 may be provided in the vanes 22. The flow characteristics through the outlet 38 are made the same as those through the holes 26 and for this purpose, the gas passage between the inner body 28 and tail pipe 20 is of greater radial dimension Ro when the vanes 22 are operative than the radial dimension Rr when the vanes 22 are inoperative. In a modification, Fig. 5 (not shown), the nozzle is of convergent-divergent form when the vanes 22 are in the inoperative position. In this arrangement the vanes 22 carry the sealing flaps which block the gaps between the vanes when they are in the operative position. Pivoting flaps are also provided to block off the apertures 24 when the vanes 22 are in the inoperative position. In a further modification, Fig. 11 (not shown), an additional set of hollow vanes is pivoted on the outside of the tail pipe 20. In this arrangement, when the vanes are in the operative position, the outer set of vanes block the gaps between the inner set of vanes so that no sealing flaps are required. The outer flaps, when inoperative, are enclosed by a nacelle having automatically operated doors through which the vanes pass in moving between the operative and inoperative positions.