Ducted fan gas turbine engine with secondary duct

The fan duct 12 of a ducted fan gas turbine engine 10 is provided with a secondary duct 24 at least partly within the downstream end of the primary duct. The secondary duct 24 is provided with means such as a translatable, jet pipe 30, flaps (34)(Fig.2) or (36)(figs. 3 and 4), whereby the airflow therethrough may be varied to suit flight requirements of an associated aircraft, in a way which will control the maximum diameter of the free stream tube airflow at the intake of the engine, thus effectively reducing the frontal area of the fan duct, and therefor, drag. Flow from the secondary duct 24 may be diverted into the main by-pass flow (fig. 2) or the core flow (figs. 3 and 4), via conduits (38) in the latter case.