Hybrid aircraft propulsion system
A hybrid aircraft propulsion system. The system comprises a gas turbine engine comprising a compressor, a combustor, one or more turbines, a shaft coupled to one of the turbines, and a bypass fan mechanically driven by the shaft. The system further comprises an electrical generator mechanically coupled to the shaft, and an auxiliary propulsor mechanically coupled to an electric motor and electrically coupled to the electric generator. At maximum power, the gas turbine engine is configured to produce a turbine entry temperature at maximum power between 1800 Kelvin and 2000 Kelvin, the engine comprises a fan bypass ratio of between 4:1 and 13:1, and the generator is configured to absorb between 10% and 60% of the mechanical power generated by the turbine.
1. A hybrid aircraft propulsion system comprising:
a gas turbine engine comprising a compressor, a combustor, one or more turbines, a shaft coupled to one turbine of the one or more turbines, and a direct drive bypass fan mechanically driven by the shaft;
an electrical generator mechanically coupled to the shaft;
an auxiliary propulsor mechanically coupled to an electric motor, and electrically coupled to the electric generator;
wherein, at maximum power of the gas turbine engine:
the gas turbine engine is configured to produce a turbine entry temperature between 1800 Kelvin and 2000 Kelvin,
the gas turbine engine comprises a fan bypass ratio of between 5:1 and 10:1, and
the generator is configured to absorb between 10% and 60% of mechanical power generated by the one turbine,
wherein the direct drive bypass fan has a fan tip pressure ratio at the maximum power of the gas turbine engine of greater than 1.1 and less than 1.4,
wherein a ratio of the fan bypass ratio to a turbine pressure ratio of the one turbine is between 1 and 2,
wherein the one turbine has a turbine pressure ratio that is greater than 5, and
wherein the one turbine comprises between three stages and six stages, inclusive of three stages and six stages.
2. The system according to claim 1 , wherein the direct drive bypass fan is coupled to the one turbine such that the bypass fan and one turbine rotate at the same rotational speed in use.
3. The system according to claim 1 , wherein the auxiliary propulsor is configured to ingest a boundary layer airflow in flight.
4. The system according to claim 1 , wherein the one turbine comprises a low pressure turbine and the compressor comprises a low pressure compressor, wherein the gas turbine engine further comprises a high pressure compressor and a high pressure turbine.
5. The system according to claim 4 , wherein the shaft comprises a low pressure shaft, wherein the low pressure turbine is coupled to the low pressure compressor, the generator and the direct drive bypass fan by the low pressure shaft, and the high pressure turbine is coupled to the high pressure compressor by a high pressure shaft.
6. An aircraft comprising a hybrid aircraft propulsion system according to claim 1 .
7. The aircraft according to claim 6 , wherein the auxiliary propulsor is located such that an inlet is located adjacent an aft region of the aircraft, and comprises an outlet adjacent an aft portion of the aircraft.