A core engine of a variable cycle gas turbine engine includes a low pressure spool for generating streams of bypass air and pressurized air, and a high pressure spool for further pressurizing the stream of pressurized air to generate streams of combustion air and supercharged auxiliary air. A peripheral case surrounds the engine case to form a peripheral duct. An auxiliary combustor and propulsor are positioned within the peripheral duct. A bleed duct extends from the high pressure spool to the auxiliary combustor. Variable ductwork directs airflow through the bleed duct and peripheral duct in two modes. A first mode comprises directing the stream of auxiliary air to the auxiliary combustor, and directing stream of inlet air through the peripheral duct. A second mode comprises directing the stream of auxiliary air into the stream of bypass air, and preventing inlet air from entering the peripheral duct.