Geared gas turbine engine
An engine for an aircraft includes an engine core having a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan having a plurality of fan blades; a fan shaft; a gearbox that receives an input from the core shaft and outputs drive to the fan via the fan shaft so as to drive the fan at a lower rotational speed than the core shaft, the gearbox being an epicyclic gearbox having a sun gear, a plurality of planet gears, a ring gear, and a planet carrier on which the planet gears are mounted; and a gearbox support arranged to mount the gearbox within the engine. The fan shaft, core shaft, gearbox and the gearbox support together may form a transmission.
1. A gas turbine engine for an aircraft comprising:
an engine core comprising a turbine, a compressor, a gearbox, a gearbox support arranged to mount the gearbox within the gas turbine engine, and a core shaft connecting the turbine to the compressor;
a fan located upstream of the gas turbine engine core, the fan comprising a plurality of fan blades; and
a fan shaft;
the gearbox being arranged to receive an input from the core shaft and to output drive to the fan via the fan shaft 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 plurality of planet gears are mounted, and the gearbox having an overall gear mesh stiffness;
the fan shaft, the core shaft, the gearbox, and the gearbox support together forming a transmission having an effective linear torsional stiffness,
and wherein a gear mesh to transmission stiffness ratio of:
the
overall
gear
mesh
stiffness
of
the
gearbox
the
effective
linear
torsional
stiffness
of
the
transmission
is greater than or equal to 0.34 and less than or equal to 11.0.
2. The gas turbine engine of claim 1 , wherein either:
(i) the fan has a fan diameter in the range from 240 to 280 cm, and the gear mesh to transmission stiffness ratio is in the range from 1.4 to 2.7; or
(ii) the fan has a fan diameter in the range from 330 to 380 cm, and the gear mesh to transmission stiffness ratio is in the range from 0.5 to 4.6.
3. The gas turbine engine of claim 1 wherein the gearbox has a gearbox diameter defined as the pitch circle diameter of the ring gear, and the gearbox diameter is in the range from 0.55 m to 1.2 m.
4. The gas turbine engine of claim 1 wherein at least one of:
(i) a gear mesh stiffness between the plurality of planet gears and the ring gear is greater than or equal to 1.40×10 9 N/m and less than or equal to 1.05×10 10 N/m; and
(ii) a gear mesh stiffness between the plurality of planet gears and the sun gear is greater than or equal to 1.20×10 9 N/m and less than or equal to 9.5×10 9 N/m.
5. The gas turbine engine according to claim 1 , wherein:
the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft;
the gas turbine engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor; and
the second turbine, the second compressor, and the second core shaft are arranged to rotate at a higher rotational speed than the first core shaft.
6. The gas turbine engine according to claim 1 , wherein the planet carrier comprises a forward plate and a rearward plate and pins extending therebetween, each respective pin being arranged to have a planet gear mounted on each respective pin between the forward plate and the rearward plate, and wherein the planet carrier further comprises lugs extending between the forward and rearward plates, the lugs being arranged to pass between adjacent planet gears.
7. The gas turbine engine according to claim 1 , wherein:
(i) the gearbox comprises an odd number of planet gears; and/or
(ii) the fan has a fan diameter greater than 240 cm and less than or equal to 380 cm.
8. A gas turbine engine for an aircraft comprising:
an engine core comprising a turbine, a compressor, a gearbox, a gearbox support arranged to mount the gearbox within the gas turbine engine, the gearbox support having an effective linear torsional stiffness, and a core shaft connecting the turbine to the compressor;
a fan located upstream of the gas turbine engine core, the fan comprising a plurality of fan blades; and
a fan shaft;
the gearbox being arranged to receive an input from the core shaft and to output drive to the fan via the fan shaft 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 plurality of planet gears are mounted, and the gearbox having an overall gear mesh stiffness; and
wherein a gear mesh to gearbox support stiffness ratio of:
the
overall
gear
mesh
stiffness
of
the
gearbox
the
effective
linear
torsional
stiffness
of
the
gearbox
support
is greater than or equal to 6.5×10 −2 and less than or equal to 2.6×10 1 .
9. The gas turbine engine of claim 8 wherein the gear mesh to gearbox support stiffness ratio is greater than or equal to 2.6×10 −1 and less than or equal to 2.6×10 1 .
10. A gas turbine engine for an aircraft comprising:
an engine core comprising a turbine, a compressor, a gearbox, a gearbox support arranged to mount the gearbox within the gas turbine engine, and a core shaft connecting the turbine to the compressor, the core shaft having an effective linear torsional stiffness;
a fan located upstream of the gas turbine engine core, the fan comprising a plurality of fan blades; and
a fan shaft, the fan shaft having an effective linear torsional stiffness;
the gearbox being arranged to receive an input from the core shaft and to output drive to the fan via the fan shaft 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 plurality of planet gears are mounted, and the gearbox having an overall gear mesh stiffness;
and wherein:
(i) a gear mesh to fan shaft stiffness ratio of:
the
overall
gear
mesh
stiffness
of
the
gearbox
the
effective
linear
torsional
stiffness
of
the
fan
shaft
is in the range from 0.3 to 1.6; or
(ii) a gear mesh to core shaft stiffness ratio of:
the
overall
gear
mesh
stiffness
of
the
gearbox
the
effective
linear
torsional
stiffness
of
the
core
shaft
is greater than or equal to 0.20 to 90.