High power epicyclic gearbox and operation thereof

1. 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, the fan having a fan axial centreline;

a gearbox that is configured to:

receive an input from the core shaft, and

output drive to a fan shaft via an output of the gearbox 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 engine, the fan shaft mounting structure comprising at least two supporting bearings connected to the fan shaft, wherein:

the fan comprises 22, 24 or 26 fan blades;

a system radial bending stiffness is defined as:

1

(

1

a

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

mounting

⁢

structure

)

+

(

1

a

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

at

⁢

the

⁢

output

⁢

of

⁢

the

⁢

gearbox

)

;

a system tilt stiffness is defined as:

1

(

1

a

⁢

tilt

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

mounting

⁢

structure

)

+

(

1

a

⁢

tilt

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

at

⁢

the

⁢

output

⁢

of

⁢

the

⁢

gearbox

)

;

and

either: (i) the system radial bending stiffness is greater than or equal to 3.90×10 6 N/m; or (ii) the system tilt stiffness is greater than or equal to 1.10×10 5 Nm/rad.

2. The gas turbine engine according to claim 1 , wherein a fan shaft mounting radial bending stiffness ratio of:

the

⁢

system

⁢

radial

⁢

bending

⁢

stiffness

the

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

⁢

the

fan

⁢

shaft

⁢

mounting

⁢

structure

is in the range from 1.0×10 −3 to 4.0×10 −1 .

3. The gas turbine engine according to claim 1 , wherein a fan shaft mounting tilt stiffness ratio of:

the

⁢

system

⁢

tilt

⁢

stiffness

the

⁢

tilt

⁢

stiffness

⁢

of

⁢

the

fan

⁢

shaft

⁢

mourting

⁢

structure

is in the range from 1.5×10 −3 to 5.0×10 −1 .

4. The gas turbine engine according to claim 1 , wherein at least one of the following is satisfied:

a) the system radial bending stiffness is in a range from 3.90×10 6 N/m to 1.40×10 9 N/m;

b) the radial bending stiffness of the fan shaft mounting structure is greater than or equal to 7.00×10 8 N/m; and

c) the radial bending stiffness of the fan shaft at the output of the gearbox is greater than or equal to 4.00×10 6 N/m.

5. The gas turbine engine according to claim 1 , wherein at least one of the following is satisfied:

a) the gearbox has a gear ratio of between 3 and 3.1;

b) an axial distance between an input to the fan and a closest bearing of the at least two supporting bearings in a rearward direction from the fan is in a range from 0.12 m to 0.40 m;

c) a fan tip loading is configured to be in a range from 0.30 to 0.34 at cruise conditions, where the fan tip loading is defined as dH/U tip 2 , where dH is an enthalpy rise across the fan and U tip is a translational velocity of a fan tip of the fan; and

d) the at least two supporting bearings comprise a first supporting bearing and second supporting bearing, wherein both of the first and the second supporting bearings are located at positions forward of the gearbox.

6. The gas turbine engine according to claim 1 , wherein at least one of the following is satisfied:

a) the fan has a diameter in a range of 220 cm to 240 cm;

b) a first bearing separation product defined as:

a first bearing separation distance×an axial distance between a fan input position and a gearbox output position

is in a range from 5.2×10 −2 m 2 to 2.6×10 −1 m 2 ;

c) the fan blades are manufactured using a titanium based metal; and

d) a temperature of a flow at an exit to the combustor is configured to be greater than 1600K at cruise conditions.

7. 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, the fan having a fan axial centreline;

a gearbox that is configured to:

receive an input from the core shaft, and

output drive to a fan shaft via an output of the gearbox 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 engine, the fan shaft mounting structure comprising at least two supporting bearings connected to the fan shaft, wherein:

the fan blades are manufactured using a titanium based metal;

a system radial bending stiffness is defined as:

1

(

1

a

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

mounting

⁢

structure

)

+

(

1

a

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

at

⁢

the

⁢

output

⁢

of

⁢

the

⁢

gearbox

)

;

a system tilt stiffness is defined as:

1

(

1

a

⁢

tilt

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

mounting

⁢

structure

)

+

(

1

a

⁢

tilt

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

at

⁢

the

⁢

output

⁢

of

⁢

the

⁢

gearbox

)

;

and

either: (i) the system radial bending stiffness is greater than or equal to 3.90×10 6 N/m; or (ii) the system tilt stiffness is greater than or equal to 1.10×10 5 Nm/rad.

8. The gas turbine engine according to claim 7 , wherein a fan shaft mounting radial bending stiffness ratio of:

the

⁢

system

⁢

radial

⁢

bending

⁢

stiffness

the

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

⁢

the

fan

⁢

shaft

⁢

mounting

⁢

structure

is in a range from 1.0×10 −3 to 4.0×10 −1 .

9. The gas turbine engine according to claim 7 , wherein a fan shaft mounting tilt stiffness ratio of:

the

⁢

system

⁢

tilt

⁢

stiffness

the

⁢

tilt

⁢

stiffness

⁢

of

⁢

the

fan

⁢

shaft

⁢

mounting

⁢

structure

is in a range from 1.5×10 −3 to 5.0×10 −1 .

10. The gas turbine engine according to claim 7 , wherein at least one of the following is satisfied:

a) the system radial bending stiffness is in a range from 3.90×10 6 N/m to 1.40×10 9 N/m;

b) the radial bending stiffness of the fan shaft mounting structure is greater than or equal to 7.00×10 8 N/m; and

c) the radial bending stiffness of the fan shaft at the output of the gearbox is greater than or equal to 4.00×10 6 N/m.

11. The gas turbine engine according to claim 7 , wherein at least one of the following is satisfied:

a) the gearbox has a gear ratio of between 3 and 3.1;

b) an axial distance between an input to the fan and a closest bearing of the at least two supporting bearings in a rearward direction from the fan is in a range from 0.12 m to 0.40 m;

c) a fan tip loading is configured to be in a range from 0.30 to 0.34 at cruise conditions, where the fan tip loading is defined as dH/U tip 2 , where dH is an enthalpy rise across the fan and U tip is a translational velocity of a fan tip of the fan; and

d) the at least two supporting bearings comprise a first supporting bearing and second supporting bearing, wherein both of the first and the second supporting bearings are located at positions forward of the gearbox.

12. The gas turbine engine according to claim 7 , wherein at least one of the following is satisfied:

a) the fan has a diameter in a range of 220 cm to 240 cm; and

b) a first bearing separation product defined as:

a first bearing separation distance×an axial distance between a fan input position and a gearbox output position

is in a range from 5.2×10 −2 m 2 to 2.6×10 −1 m 2 ;

c) the fan comprises 22, 24 or 26 fan blades; and

d) a temperature of a flow at an exit to the combustor is configured to be greater than 1600K at cruise conditions.

13. 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, the fan having a fan axial centreline;

a gearbox that is configured to:

receive an input from the core shaft, and

output drive to a fan shaft via an output of the gearbox 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 engine, the fan shaft mounting structure comprising at least two supporting bearings connected to the fan shaft, wherein:

a temperature of a flow at an exit to the combustor is configured to be greater than 1600K at cruise conditions;

a system radial bending stiffness is defined as:

1

(

1

a

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

mounting

⁢

structure

)

+

(

1

a

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

at

⁢

the

⁢

output

⁢

of

⁢

the

⁢

gearbox

)

;

a system tilt stiffness is defined as:

1

(

1

a

⁢

tilt

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

mounting

⁢

structure

)

+

(

1

a

⁢

tilt

⁢

stiffness

⁢

of

the

⁢

fan

⁢

shaft

⁢

at

⁢

the

⁢

output

⁢

of

⁢

the

⁢

gearbox

)

;

and

either: (i) the system radial bending stiffness is greater than or equal to 3.90×10 6 N/m; or (ii) the system tilt stiffness is greater than or equal to 1.10×10 5 Nm/rad.

14. The gas turbine engine according to claim 13 , wherein a fan shaft mounting radial bending stiffness ratio of:

the

⁢

system

⁢

radial

⁢

bending

⁢

stiffness

the

⁢

radial

⁢

bending

⁢

stiffness

⁢

of

⁢

the

fan

⁢

shaft

⁢

mounting

⁢

structure

is in a range from 1.0×10 −3 to 4.0×10 −1 .

15. The gas turbine engine according to claim 13 , wherein a fan shaft mounting tilt stiffness ratio of:

the

⁢

system

⁢

tilt

⁢

stiffness

the

⁢

tilt

⁢

stiffness

⁢

of

⁢

the

fan

⁢

shaft

⁢

mounting

⁢

structure

is in a range from 1.5×10 −3 to 5.0×10 −1 .

16. The gas turbine engine according to claim 13 , wherein at least one of the following is satisfied:

a) the system radial bending stiffness is in a range from 3.90×10 6 N/m to 1.40×10 9 N/m;

b) the radial bending stiffness of the fan shaft mounting structure is greater than or equal to 7.00×10 8 N/m; and

c) the radial bending stiffness of the fan shaft at the output of the gearbox is greater than or equal to 4.00×10 6 N/m.

17. The gas turbine engine according to claim 13 , wherein at least one of the following is satisfied:

a) the gearbox has a gear ratio of between 3 and 3.1;

b) an axial distance between an input to the fan and a closest bearing of the at least two supporting bearings in a rearward direction from the fan is in a range from 0.12 m to 0.40 m;

c) a fan tip loading is configured to be in a range from 0.30 to 0.34 at cruise conditions, where the fan tip loading defined as dH/U tip 2 , where dH is an enthalpy rise across the fan and U tip is a translational velocity of a fan tip of the fan;

d) the at least two supporting bearings comprise a first supporting bearing and second supporting bearing, wherein both of the first and the second supporting bearings are located at positions forward of the gearbox.

18. The gas turbine engine according to claim 13 , wherein at least one of the following is satisfied:

a) the fan has a diameter in a range of 220 cm to 240 cm;

b) a first bearing separation product defined as:

a first bearing separation distance×an axial distance between a fan input position and a gearbox output position

is in a range from 5.2×10 −2 m 2 to 2.6×10 −1 m 2 ;

c) the fan comprises 22, 24 or 26 fan blades; and

d) the fan blades are manufactured using a titanium based metal.