GB723406A - Improvements in or relating to aircraft jet engine cooling system - Google Patents

Abstract

723,406. Gas-turbine jet-propulsion engines. NORTHROP AIRCRAFT, Inc. Dec. 29, 1952, No. 32835/52. Class 110 (3). [Also in Group XXXIII] An aircraft having a gas-turbine jet-propulsion engine having a shroud surrounding at least a portion of the engine through which cooling air is passed from the engine inlet duct to the jet-propulsion nozzle which acts as an ejector, has means for admitting cooling air at atmospheric pressure to the shroud when both the inlet duct and the outlet in the jet-propulsion nozzle are at negative pressure. Air is supplied to the intake 11 of a gas-turbine jet-propulsion engine through a short inlet duct 10. The front end of the intake 11 is spaced from the rear end of the duct 10 by spacers 15 which form an annular inlet to the duct 17. A shroud 18 cantilevered from a flange 19 on the engine casing extends rearwardly around the combustion and turbine section 21 and tail pipe section 22 to an opening 6 which is beyond the rear of the tail pipe 22. The shroud 18 forms a cooling space 17a to which air is led by a duct 16a having flame traps 20. With the engine running the jet of hot gases passing through the propulsion nozzle 24 will cause a negative pressure to be developed at the rear end of the shroud and air to be drawn through the passages 17, 17a. When the airplane is stationary with the engine running, a negative pressure is also developed in the inlet duct 10. A flap valve 31, Fig. 4, at the inlet duct then opens and air flows through the duct 16a and then divides; part flows forwardly through the passage 17 to the inlet duct 10 and part flows rearwarldy through the duct 17a towards the jet-propulsion nozzle. When the aircraft is in flight, a positive ram pressure exists in the duct 10, and a negative pressure at the rear end of the shroud. The cooling air will then flow as shown in Fig. 2 from the duct 10, passage 17, inlet duct 16a and passage 17a to the propulsion nozzle. To cause the flap valve 31 to open and close under the correct conditions, the duct 16a has its inlet 30 arranged in the engine casing 3 at a position where the pressure is zero when the aircraft is stationary and negative when the aircraft is in flight. The valve 31 is preferably formed of impregnated cloth attached to a flush plate 33 but it may be formed by a hinged metal door. With the arrangement described, the normal heat-insulating blanket may be replaced by a polished stainless-steel heat shield 35 supported from the shroud 18 by members 36. A baffle 39 is provided to equalize the air flow around the engine. Specification 591,736 is referred to.