AIRCRAFT HYBRID PROPULSION SYSTEM

An aircraft hybrid propulsion system (5) comprises an internal combustion engine (10), an electric motor (28) a propulsor (12) and a combining gearbox (36). The internal combustion engine (10) is coupled to a first input (62) of the combining gearbox (36), the electric motor (28) is coupled to a second input (64) of the combining gearbox (36), and the propulsor (12) is coupled to an output (68) of the combining gearbox (36), such that the propulsor (12) is driveable in use by either or both of the internal combustion engine(10) and the electric motor (28). Each of the internal combustion engine (10) and the electric motor (28) is coupled to its respective input by a respective clutch (50, 52).