PURPOSE: To strengthen the thrust of an aircraft by providing a vortex generating mechanism at the rear of a main wing to accelerate the mixture of engine exhaust stream flowing along the upper surface of the main wing and the stream along the lower surface of the main wing flowing into the upper surface of the flap.

CONSTITUTION: The exhaust nozzle 2 of an engine 1 installed at the front upper portion of a main wing 4 incorporates an opening 2a formed in flat manner laterally to flow the exhaust 3 along the upper surface of the wing 4. When the flap 5 is lowered to predetermined downward angle, the air stream flowing along the lower surface of the wing 4 is partly passed through a throat 7 formed between the trailing edge of the main wing 4 and the front edge of the front flap 5a to thus flow toward the upper surface of the flap. It will mix with the exhaust stream 3 of the engine to become the stream 10 having large momentum to then flow into downward so as to obtain strengthened thrust. A vortex generator 8 provided at the trailing edge of the main wing 4 generates vortex 9 to accelerate the mixture of the exhaust stream 3 with the induction flow 6 so as to strengthen the thrust.