Propulsion systems for low observable aircraft

A propulsion system for an aircraft having a body, the aircraft operable to transition between thrust-borne lift in a VTOL orientation and wing-borne lift in a forward flight orientation, the propulsion system comprising:

• a turboshaft engine disposed within the body, the engine having a turboshaft mode and a turbofan mode, the engine configured to generate engine exhaust;
• a lift fan system disposed within the body, the lift fan system including at least one ducted fan;
• a forced air bypass system disposed within the body, the forced air bypass system configured to generate bypass air;
• a transmission disposed between the engine and the forced air bypass system, the transmission engaging the engine with the forced air bypass system when the engine is in the turbofan mode and disengaging the engine from the forced air bypass system when the engine is in the turboshaft mode;
• and
• an exhaust system coupled to the engine and the forced air bypass system;
• wherein, in the VTOL orientation, the engine is in the turboshaft mode coupled to the lift fan system such that the engine provides rotational energy to the at least one ducted fan generating the thrust-borne lift;
• and
• wherein, in the forward flight orientation, the engine is in the turbofan mode coupled to the forced air bypass system such that the bypass air combines with the engine exhaust in the exhaust system to provide forward thrust generating the wing-borne lift.