An aircraft has a wing 10 supporting at its underside a gas turbine engine 13. A jet pipe 14 of the engine has an exhaust nozzle 15 of rectangular flow area defined by upper and lower panels 16,17 and end walls 18. The upper panel, which is a part common to the nozzle and to a trailing edge portion of the wing, comprises a pair of flaps 20,21 which are pivotal between a position of alignment with the wing 10 and a position in which they are inclined to the wing. A part of the gas flowing through the jet pipe is diverted through a passage 25 into a passage 26 defined between the flaps 20,21 so as to entrain and accelerate air 26A flowing over the wing 10. This increases the lift of the wing at the rear thereof and also increases the thrust developed at the nozzle 15. This in turn helps to compensate for a nose-up moment on the aircraft arising from the thrust 13D2 of the engine passing forward of the centre of gravity 9A of the aircraft.