Reliable gearbox for gas turbine engine

A method of operation of 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;
• and
• a gearbox arranged to receive an input from the core shaft and to output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox being an epicyclic gearbox comprising a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the planet gears are mounted, the planet carrier having an effective linear torsional stiffness and the gearbox having a gear mesh stiffness between the planet gears and the ring gear, and wherein:
• the product of the effective linear torsional stiffness of the planet carrier and the gear mesh stiffness between the planet gears and the ring gear is greater than or equal to 5.0×1018 N2m−2
• the method comprising operating the gas turbine engine to provide propulsion under cruise conditions.

A propulsor for an aircraft comprising:

• a fan comprising a plurality of fan blades;
• a gearbox;
• and
• a power unit for driving the fan via the gearbox;
• wherein the gearbox is an epicyclic gearbox arranged to receive an input from a core shaft driven by the power unit and to output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, and comprises a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the planet gears are mounted, the planet carrier having an effective linear torsional stiffness and the gearbox having a gear mesh stiffness between the planet gears and the ring gear, and wherein:
• the product of the effective linear torsional stiffness of the planet carrier and the gear mesh stiffness between the planet gears and the ring gear is greater than or equal to 5.0×1018 N2m−2.