Improvements in or relating to aircraft jet propulsion units

870,853. Gas-turbine engines; jet-propulsion engines. NAPIER & SON Ltd., D. May 22, 1958 [July 3, 1957], No. 21206/57. Class 110 (3). In a turbine and compressor assembly forming part of an aircraft jet-propulsion unit the turbine and compressor rotors are coupled to one another through a uni-directional clutch whereby the compressor may overrun the turbine or free-wheel or windmill when the turbine is stationary. The engine shown is a combined gas turbine and ram-jet unit and comprises an axial-flow compressor 15 mounted on a shaft 27 which may be connected to the shaft 29, on which the turbine 30 is mounted, by means of a unidirectional clutch 28. The turbine 30 is supplied with combustion gases from a rocket-type combustion chamber 32, hydrogen peroxide being supplied to the catalyst chamber 31 and kerosene fuel being burned in the resulting mixture of steam and oxygen. The exhaust gases from the turbine pass through ducts 33 to enter the main combustion chamber 17, finally discharging through propulsion nozzle 19. The compressor 15 when driven by the turbine, takes in air through the annular intake 13 and diffuser passage 14 and discharges it to the annular duct 16 from which it enters the main combustion chamber 17 where kerosene fuel supplied through injectors 18 is burned in it. The hot combustion gases discharge through the propulsion nozzle 19 which is controlled by an axially-movable bullet 20. During this operation the annular air duct 35 formed around the compressor 15 between the outer casing 10 and the outer wall of the compressor is closed at its downstream and by means of the pivoted flap valves 36. Also, the flap valves 41 are open in the chain-dotted position so as to provide an additional annular air intake around the main intake 13. At a certain flight velocity, the supply of fuel and oxidant to the rocket-type combustion chamber is cut-off so that the turbine stops and the clutch 28 is moved so that the compressor 15 can windmill without rotating the turbine. At the same time, the flap valves 36 are opened and the flap valves 41 are closed so that ram air flows through the intake 13, diffuser passage 14, the compressor channel, and the annular passage 35, through the annular passage 16 to the main combustion chamber 17, the supply of kerosene fuel through the injectors 18 being continued, so that the engine functions simply as a ram-jet unit. During this operation, the compressor outlet guide vanes 39 are rotated on their pins to the f