AIRCRAFT PROPULSION SYSTEM

An aircraft propulsion system (5) comprises a propulsor (12), a motor (28) and a reduction gearbox (16) coupled to a prime mover (28) at an input side, and the propulsor (12) at an output side. The reduction gearbox (16) is configured to provide a reduction ratio between the input and output. The reduction gearbox is configured such that the input side rotates in an opposite direction to the output side, and the prime mover (28), motor (28), propulsor (12) and reduction gearbox (16) are configured such that gyroscopic forces of the propulsor, motor, prime mover and reduction gearbox generated during aircraft manoeuvres and / or propulsion system failures are substantially cancelled.