Aircraft engine

A propulsor for an aircraft, comprising:

• a fan comprising a plurality of fan blades;
• a gearbox;
• a power unit for driving the fan via the gearbox, wherein the gearbox is arranged to receive an input from the power unit via a core shaft and output drive to a fan shaft so as to drive the fan at a lower rotational speed than the core shaft;
• and
• a fan shaft mounting structure arranged to mount the fan shaft within the propulsor, wherein the fan shaft mounting structure comprises at least two supporting bearings connected to the fan shaft, wherein:
• the output of the gearbox is at a gearbox output position and the input to the fan is at a fan input position;
• a first bearing separation distance (d1) is defined as the axial distance between the input to the fan and the closest bearing of the at least two supporting bearings in a rearward direction from the fan;
• and
• a first bearing separation ratio of:
• the
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• distance
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• axial
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• distance
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• fan
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• position
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• gearbox
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• output
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• d
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• is greater than or equal to 1.6×10−1, and the axial distance between the fan input position and the gearbox output position (d4) is greater than or equal to 0.43 m.

A method of operating a gas turbine engine for an aircraft comprising:

• an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor;
• a fan located upstream of the engine core, the fan comprising a plurality of fan blades;
• a gearbox that receives an input from the core shaft and outputs drive via an output of the gearbox to a fan shaft so as to drive the fan via an input to the fan at a lower rotational speed than the core shaft;
• and
• a fan shaft mounting structure arranged to mount the fan shaft within the engine, wherein the fan shaft mounting structure comprises at least two supporting bearings connected to the fan shaft, wherein:
• the output of the gearbox is at a gearbox output position and the input to the fan is at a fan input position;
• a first bearing separation distance (d1) is defined as the axial distance between the input to the fan and the closest bearing of the at least two supporting bearings in a rearward direction from the fan;
• and
• a first bearing separation ratio of:
• the
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• first
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• bearing
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• 
• separation
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• distance
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• (
• d
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• )
• the
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• axial
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• distance
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• between
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• the
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• fan
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• input
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• position
• and
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• the
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• gearbox
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• output
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• position
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• (
• d
• 4
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• is greater than or equal to 1.6×10−1, and the axial distance between the fan input position and the gearbox output position (d4) is greater than or equal to 0.43 m, the method comprising operating the gas turbine engine to provide propulsion for the aircraft under cruise conditions.