Gearboxes for aircraft gas turbine engines

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 configured to receive an input from the core shaft and provide an output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox comprising:
• a sun gear;
• a plurality of planet gears surrounding and engaged with the sun gear;
• and
• a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin, wherein:
• the journal bearing has a diametral clearance that is between 0.1% and 0.3% of a diameter of the journal bearing;
• the gearbox has a gear ratio in the range 3 to 3.9;
• the ratio of the radius of the fan blade at the hub to the radius of the fan blade at the tip is in the range 0.25 to 0.33;
• and
• the gas turbine engine is configured such that during operation a maximum operating sliding speed of each journal bearing is in the range 30 m/s to 50 m/s.

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 configured to receive an input from the core shaft and provide an output drive to the fan so as to drive the fan at a lower rotational speed than the core shaft, the gearbox comprising:
• a sun gear;
• a plurality of planet gears surrounding and engaged with the sun gear;
• and
• a ring gear surrounding and engaged with the plurality of planet gears, each of the plurality of planet gears being rotatably mounted around a pin of a planet gear carrier with a journal bearing having an internal sliding surface on the planet gear and an external sliding surface on the pin, wherein:
• the journal bearing has a diametral clearance that is between 0.1% and 0.3% of a diameter of the journal bearing;
• the gearbox has a gear ratio of at least 4.2;
• and
• the gas turbine engine is configured such that during operation at least one of the following is true:
• 1) a maximum operating sliding speed of each journal bearing is in the range 30 m/s to 50 m/s;
• and 2) a maximum specific load of each journal bearing is in the range 5 MPa to 20 MPa.