Abstract: An aircraft propulsion system comprises a propulsor, a motor and a reduction gearbox coupled to a prime mover at an input side, and the propulsor at an output side. The reduction gearbox 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, motor, propulsor and reduction gearbox 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.

Abstract: An aircraft propulsion system comprises a propulsor, a motor and a reduction gearbox coupled to a prime mover at an input side, and the propulsor at an output side. The reduction gearbox 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, motor, propulsor and reduction gearbox 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.

Abstract: A procedure defining a balancing strategy includes: providing a computer model which predicts the vibration amplitude at a given axial position along the spool when the spool is rotated at a given rotational speed; using the model to predict respective vibration amplitudes at the given axial position for different axial positions of a unit unbalance applied to the spool; plotting the predicted vibration amplitudes as data points on a graph of vibration amplitude against axial position of the applied unit unbalance; using the graph to identify axial positions which are more or less likely to contribute to flexing of the spool at the given rotational speed when mass is added or removed from the first rotor module to reduce imbalances at the axial positions; and defining a balancing strategy based on the identification.

Abstract: A procedure defining a balancing strategy includes: providing a computer model which predicts the vibration amplitude at a given axial position along the spool when the spool is rotated at a given rotational speed; using the model to predict respective vibration amplitudes at the given axial position for different axial positions of a unit unbalance applied to the spool; plotting the predicted vibration amplitudes as data points on a graph of vibration amplitude against axial position of the applied unit unbalance; using the graph to identify axial positions which are more or less likely to contribute to flexing of the spool at the given rotational speed when mass is added or removed from the first rotor module to reduce imbalances at the axial positions; and defining a balancing strategy based on the identification.