Supersonic aircraft turbofan

A method of operating a supersonic aircraft having a turbofan engine which provides propulsive thrust to the supersonic aircraft over a range of flight operations including a transonic push operation during which the supersonic aircraft transitions from subsonic flight to supersonic flight, and a supersonic cruise operation, which has a relatively lower thrust than the transonic push operation, the turbofan engine including:

• an engine core including, in flow series, a compressor, a combustor, and a turbine;
• a fan located upstream of the engine core;
• a supersonic intake configured to decrease air velocities of incoming air to subsonic velocities at an inlet to the fan formed by the intake;
• a bypass duct surrounding the engine core, the fan being configured to generate a core airflow to the engine core and to generate a cold bypass airflow through the bypass duct;
• a variable mixer configured to mix a hot exhaust gas flow exiting the engine core with the cold bypass airflow exiting the bypass duct, the mixer being configured to vary a cross-sectional area of a hot inlet of the mixer for the hot exhaust gas flow and a cross-sectional area of a cold inlet of the mixer for the cold bypass airflow to change a ratio of an amount of the hot exhaust gas flow relative to an amount of the cold bypass airflow that is mixed by the mixer;
• and
• a thrust nozzle located rearwards of the mixer, the thrust nozzle being configured to discharge the exhaust gas flow and the bypass airflow mixed by the mixer, the thrust nozzle having a variable area throat defining a cross- sectional throat area, the thrust nozzle being configured to controllably vary the throat area,
• the method comprising:
• performing a ground subsonic take-off operation by controlling the thrust nozzle to reduce the throat area of the variable area throat, which increases the thrust of the turbofan engine;
• and
• transitioning the supersonic aircraft after the take-off operation to perform an off-the-ground subsonic climb operation by controlling the thrust nozzle to increase the throat area of the variable area throat, and controlling the mixer to increase the cross-sectional area of the hot inlet and decrease the cross-sectional area of the cold inlet, which increase the amount of hot exhaust gas flow in the ratio of the hot exhaust gas flow relative to the cold bypass airflow, such that a value of (AHOTafter/ACOLDafter)/(AHOTbefore/ACOLDbefore) is in a range from 1.1 to 2.5, wherein AHOT is the cross-sectional area of the hot inlet of the mixer, ACOLD is the cross-sectional area of the cold inlet of the mixer, and subscripts “before” and “after” denote respectively immediately before and immediately after the relative increase in cross-sectional area of the hot inlet.