Dual bypass turbofan gas turbine engine

A dual bypass turbofan gas turbine engine comprising:

• a first fan and a second fan downstream of the first fan through which ambient air is propelled in an aft direction;
• a first bypass duct receiving first bypass air from the first fan, the first bypass duct including a variable area exhaust nozzle;
• a second bypass duct receiving second bypass air from the second fan;
• a core receiving core air from the second fan, the core including in serial flow communication:
• a first compressor pressurizing the core air;
• a heat exchanger facilitating heat removal from the pressurized core air;
• a second compressor further pressurizing the pressurized core air;
• a combustor in which the pressurized core air is mixed with fuel and ignited to generate a stream of combustion gas;
• and
• a turbine extracting energy from the combustion gas, a general flow direction of the combustion gas through the turbine being in a forward direction opposite the aft direction;
• a differential gear train operatively connected to split an input torque received from the turbine between the first fan and the second fan, the differential gear train having:
• an input receiving the input torque from the turbine;
• a first output delivering a first output torque to the first fan and driving the first fan in a first rotational direction;
• and
• a second output delivering a second output torque to the second fan and driving the second fan in a second rotational direction opposite the first rotational direction,
• wherein:
• the first bypass duct includes an upstream outer wall and a downstream outer wall;
• the downstream outer wall partially defines the variable area exhaust nozzle;
• the downstream outer wall is movable relative to the upstream outer wall;
• the downstream outer wall is movable between a stowed position defining a first exhaust nozzle area and a deployed position defining a second exhaust nozzle area larger than the first exhaust nozzle area;
• and
• the upstream outer wall and the downstream outer wall define an outlet therebetween for the first bypass air when the downstream outer wall is in the deployed position.