any design suitable for the purpose described herein each engine nozzle 70 is equipped with a shutter arrangement consisting of pivotable louvers 72 better seen in fig7 operated by suitable actuators such as hydraulic actuators not shown in the drawings between an open position shown in solid lining wherein the louvers 72 are oriented edge wise to the engine exhaust gases so as to offer minimum resistance to the gas flow through the nozzle and a closed condition shown in dotted lining in which the louvers 72 are transverse to the exhaust gas flow effectively closing flow through nozzle 70 actuation of the valves 66 and nozzle louvers 72 are linked so that when one is open the other is closed the open condition of the duct valves 66 is associated with a closed condition of the nozzle louvers 72 and the engine gases both bypass air and engine core exhaust are fully diverted through the side ducts 58a b 68a b into the annular spaces 42 44 for driving the fans 36 38 respectively in order to develop vertical thrust through the fan duct 26 for sustaining the aircraft 10 in hover and vertical flight in the closed condition of the duct valves 66 associated with an open condition of the nozzle louvers 72 all engine exhaust is directed to the engine nozzles 70 for developing forward thrust during winged flight intermediate positions of both the valves 66 and nozzle louvers 72 result in combined vertical and forward thrust during transitional phases of flight.