Abstract: A variable ratio bypass turbojet engine comprising a front fan core engine and a forward fan connected thereto by an inverter valve arrangement which comprises a fixed forward duct system and a fixed after duct system selectively shaped and joined by flapper valve mechanism. The flapper valve mechanism may be actuated so that the bypass ratio of the engine can be varied to produce a low bypass ratio engine during cruise operation mode wherein the front fan air is conducted to the core engine fan and the auxiliary inlet air is discharged overboard, or to a high bypass ratio engine for take-off condition mode wherein the front fan air is discharged to atmosphere through a thrust nozzle and the auxiliary inlet air is directed to the core engine fan.

Abstract: An inverter valve arrangement which comprises a fixed forward duct system having concentric annular passages at its inlet and a fixed after duct system having concentric annular passages at its outlet and each fixed system having selectively shaped adjacent portions which are circumferentially displaced and joined by a plurality of flapper valves. The flapper valves may be actuated so that either series or parallel flow will occur between the concentric annular passages of the systems.