GB875517A - Propelling nozzles for jet propulsion gas turbine engines - Google Patents

Abstract

875,517. Jet-propulsion nozzles. ROLLSROYCE Ltd. June 3, 1960 [June 12, 1959], No. 20277/59. Class 110 (3). A jet-propulsion nozzle comprising a main variable-area nozzle adapted to be mounted at, or to form part of, the downstream end of the jet pipe and an annular air duct surrounding the main nozzle provided with a secondary variable-area nozzle such that air discharged from the secondary nozzle forms an annular stream closely surrounding the jet gases discharged through the main nozzle, has means for varying the effective areas of the main and secondary nozzles which permits the effective area of the secondary nozzle to be adjusted independently of that of the main nozzle when the latter has a predetermined value. The invention is described with reference to a gas turbine engine having reheat in the jet exhaust pipe. A jet pipe 14 has a main variable-area propelling nozzle 16 formed at its downstream end. The engine and jet pipe are enclosed with a nacelle 38 which defines a by-pass passage 18 supplied with air from the engine compressor. A second variable-area nozzle 20 is provided at the downstream end of the passage 18 and the air flowing through the passage is discharged through the nozzle 20 as an annular stream closely surrounding the jet gases. The outlet end of the nozzle 16 is defined by a series of pivoted flap members 22. Each flap member 22 carries a roller 28 which co-operates with one face of a cam plate 30. The cam plates 30 are disposed in an inclined position and are carried by threaded spindles 32 forming parts of screw jacks 42. The jacks are operated together by an annular ring 44 having internal gear teeth 45. The cam plates 30 are connected together by frusto-conical rings 31. A strut 34 on each cam plate has a roller 35 which engages in a flap 36 mounted on further flap members 37. The flap members 37 are spaced downstream of the member 22 to form a duct 40 communicating with the by-pass passage 18. Each cam plate 30 has a portion 48 which is parallel to the axis of the nozzle 16 so that it is possible to adjust the position of the flaps 37 without moving the flaps 22. This allows the position of the flaps 37 to be finely adjusted to reduce thrust losses. The cam plates may have a flat portion at each end. If desired a flat portion may be formed on each cam plate at a point midway of its length whereby fine adjustment of the flaps 37 under cruise conditions can be obtained.