Geared turbofan engine gearbox arrangement

1. A turbofan engine ( 20 ) comprising:

a fan ( 28 ) having a plurality of blades;

a transmission ( 60 ) configured to drive the fan; and

three spools,

wherein:

the fan blades have a peak tip radius R T ;

the fan blades have an inboard leading edge radius R H at an inboard boundary of the flowpath;

a ratio of R H to R T is less than 0.40;

said three spools comprise:

a first spool comprising:

a first pressure turbine ( 50 ); and

a first shaft ( 56 ) coupling the first pressure turbine to the transmission;

a second spool comprising;

a second pressure turbine ( 48 );

a first compressor ( 42 ); and

a second spool shaft ( 54 ) coupling the second pressure turbine to the second spool compressor;

a core spool comprising:

a third pressure turbine ( 46 );

a second compressor ( 44 ); and

a core shaft ( 52 ) coupling the third pressure turbine to second compressor; and

a combustor ( 45 ) is between the second compressor and the third pressure turbine;

the engine comprises a plurality of main bearings wherein:

a first ( 160 ) of said main bearings engages a static support ( 164 ; 164 ′) and a forward hub ( 236 ) of the second spool; and

a second ( 162 ) of said main bearings engages the first shaft and the forward hub of the second spool;

the fan is a single-stage fan; and

a ring gear ( 82 ) of the transmission is mounted to rotate with the fan as a unit.

2. The engine of claim 1 wherein:

each fan blade has a leading edge and a trailing edge;

a splitter ( 159 ) is positioned along a flowpath through the engine and having a leading rim separates a core branch ( 506 ) of the flowpath from a bypass branch ( 510 ) of the flowpath;

an inboard boundary of the core flowpath has a radius R II at an axial position of the splitter rim;

the inboard boundary of the core flowpath has a radius R I at a leading stage of blades of the first compressor; and

a ratio of an axial length L 10 between the splitter rim and the leading stage of blades of the first compressor at the inboard boundary of the core flowpath to the radius R II is less than 1.2.

3. The engine of claim 1 wherein:

each fan blade has a leading edge and a trailing edge;

a splitter ( 159 ) is positioned along a flowpath through the engine and having a leading rim separates a core branch ( 506 ) of the flowpath from a bypass branch ( 510 ) of the flowpath;

an inboard boundary of the core flowpath has a radius R II at an axial position of the splitter rim;

the inboard boundary of the core flowpath has a radius R I at a leading stage of blades of the first compressor; and

a ratio of the radius R I to the radius R II is greater than 0.50 and is less than 1.0.

4. The engine of claim 3 wherein:

said ratio of the radius R I to the radius R II is 0.55-1.0.

5. The engine of claim 1 wherein:

the fan blades are non-variable.

6. The engine of claim 1 further comprising:

a variable fan nozzle ( 35 ).

7. The engine of claim 1 wherein:

the forward hub extends forward from a disk of the first compressor.

8. The engine of claim 7 wherein:

the forward hub extends forward from a bore ( 237 ) of the disk of the first compressor.

9. The engine of claim 1 wherein:

a separation of a transverse centerplane ( 524 ) of the first bearing and a transverse centerplane ( 526 ) of the second bearing is less than a radius (R B ) of the first bearing.

10. The engine of claim 1 wherein:

a first seal ( 290 ) seals the first bearing and a second seal ( 292 ) seals the second bearing to isolate a transmission compartment ( 286 ) ahead of the first bearing and the second bearing from a region ( 288 ) behind the first bearing and the second bearing.

11. The engine of claim 1 wherein:

the transmission comprises:

a sun gear ( 80 ) mounted to rotate with the first shaft;

said ring gear ( 82 );

a plurality of intermediate gears ( 84 ) between the sun gear and the ring gear; and

a carrier ( 86 ) holding the intermediate gears.

12. The engine of claim 1 wherein:

a third of said main bearings is a thrust bearing ( 170 ) engaging the first spool shaft.

13. The engine of claim 12 wherein:

a fourth of said main bearings is a non-thrust roller bearing ( 172 ) engaging an aft end of the first spool shaft.

14. The engine of claim 1 wherein:

the first pressure turbine has three to five blade stages.

15. The engine of claim 1 wherein:

the second spool shaft engages at least two of said main bearings, at least one of which is a thrust bearing.

16. The engine of claim 1 , wherein the ratio of R H to R T is less than 0.30.

17. A turbofan engine ( 20 ) comprising:

a fan ( 28 ) having a plurality of blades;

a transmission ( 60 ) configured to drive the fan; and

three spools,

wherein:

the fan blades have a peak tip radius R T ;

the fan blades have an inboard leading edge radius R H at an inboard boundary of the flowpath;

a ratio of R H to R T is less than 0.40;

said three spools comprise:

a first spool comprising:

a first pressure turbine ( 50 ); and

a first shaft ( 56 ) coupling the first pressure turbine to the transmission;

a second spool comprising;

a second pressure turbine ( 48 );

a first compressor ( 42 ); and

a second spool shaft ( 54 ) coupling the second pressure turbine to the second spool compressor;

a core spool comprising:

a third pressure turbine ( 46 );

a second compressor ( 44 ); and

a core shaft ( 52 ) coupling the third pressure turbine to second compressor; and

a combustor ( 45 ) is between the second compressor and the third pressure turbine;

the engine comprises a plurality of main bearings wherein:

a first ( 160 ) of said main bearings engages a static support ( 164 ; 164 ′) and a forward hub ( 236 ) of the second spool; and

a second ( 162 ) of said main bearings engages the first shaft and the forward hub of the second spool; and

the first bearing ( 160 ) and the second bearing ( 162 ) are behind the transmission ( 60 ).

18. The engine of claim 17 wherein:

the transmission comprises:

a sun gear ( 80 ) mounted to rotate with the first shaft;

a ring gear ( 82 ) mounted to rotate with the fan;

a plurality of intermediate gears ( 84 ) between the sun gear and the ring gear; and

a carrier ( 86 ) holding the intermediate gears.

19. The engine of claim 17 wherein:

the fan is a single-stage fan.

20. The engine of claim 17 wherein the ratio of R H to R T is less than 0.30.

21. A turbofan engine ( 20 ) comprising:

a fan ( 28 ) having a plurality of blades;

a transmission ( 60 ) configured to drive the fan; and

three spools,

wherein:

the fan blades have a peak tip radius R T ;

the fan blades have an inboard leading edge radius R H at an inboard boundary of the flowpath;

a ratio of R H to R T is less than 0.40;

said three spools comprise:

a first spool comprising:

a first pressure turbine ( 50 ); and

a first shaft ( 56 ) coupling the first pressure turbine to the transmission;

a second spool comprising;

a second pressure turbine ( 48 );

a first compressor ( 42 ); and

a second spool shaft ( 54 ) coupling the second pressure turbine to the second spool compressor;

a core spool comprising:

a third pressure turbine ( 46 );

a second compressor ( 44 ); and

a core shaft ( 52 ) coupling the third pressure turbine to second compressor;

a combustor ( 45 ) is between the second compressor and the third pressure turbine;

the first compressor ( 42 ) has a rear hub ( 174 ) engaging a bearing ( 170 );

said bearing engages the first shaft ( 56 ); and

another bearing ( 162 ) engages the first compressor and the first shaft.

22. The engine of claim 21 wherein:

the transmission comprises:

a sun gear ( 80 ) mounted to rotate with the first shaft;

a ring gear ( 82 ) mounted to rotate with the fan;

a plurality of intermediate gears ( 84 ) between the sun gear and the ring gear; and

a carrier ( 86 ) holding the intermediate gears.

23. The engine of claim 21 wherein:

the fan is a single-stage fan.

24. The engine of claim 21 wherein the ratio of R H to R T is less than 0.30.