Ducted fan gas turbine engine with variable area fan duct nozzle

摘要

The fan duct of a ducted fan gas turbine engine is provided with a secondary duct at least partly within the downstream end of the primary duct. The secondary duct is provided with means such as flaps 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.