Convergent-divergent plug nozzle

In a gas turbine engine including means for suppressing infrared radiation from the interior of said engine, said means comprising,

• a propulsive nozzle including an inner plug having a longitudinal section which diverges from a first diameter at the nozzle inlet to a maximum diameter and converges therebeyond;
• a casing surrounding said plug and forming a duct concentric with said plug;
• flap means pivotally connected to said casing and forming an extension thereof;
• said plug, casing, duct and flap means defining an annular nozzle coverging to a throat and diverging therebeyond wherein in a subsonic flight the flap means are disposed convergently with respect to each other and form in combination with the plug a flow path of minimum divergence for the hot gas stream, and at supersonic flight speeds are displaced outwardly to form a flow path of maximum divergence with respect to said plug;
• said flap means including a plurality of main flaps defining said throat and a plurality of secondary flaps, said secondary flaps comprising inner and outer wall members, said outer wall members being pivotally connected to the downstream end of said casing and said inner wall members being pivotally connected to the downstream end of said outer wall members, said inner and outer wall members forming a cavity therebetween;
• said nozzle including means for causing the downstream ends of said outer wall members in said subsonic flight conditions to have a diameter no greater than the said maximum diameter of said plug;
• said nozzle thereby effectively suppressing infrared radiation from the interior of said engine.