PURPOSE: To adjust a propulsion nozzle to the optimum by arranging a gas turbine jet engine and a ramjet engine in upper and lower position, and providing a partition and a nozzle flap in a exhaust duct with an end of square section.

CONSTITUTION: A gas turbine jet engine 2 and a ramjet engine 3 are arranged in upper and lower positions, a partition 14 extending to a part where a section of a propulsion nozzle 11 is narrowest is provided in the downstream direction between exhaust ducts 8, 10 with an end of square section, and nozzle flaps 12, 13 are fitted to its end. The throttling section and the divergence of the propulsion nozzle 11 are adjusted by flaps 12b, 13a, 13b by closely attaching the flaps 12a, 12b to the partition 14 during the turbo drive, by whole flaps by elevating the flaps 12a, 12b from the partition 14 during the drive of both engines, or by the flaps 12a, 12b by closely attaching the flaps 13a, 13b to the partition 14 during the drive of the ramjet. During the reverse propulsion, the nozzle is closely attached to the partition 14 on both sides of the whole flaps during the reverse propulsion, and a reverse propulsion port upstream of the flap 13a is opened.