Geared turbofan engine gearbox arrangement
A turbofan engine according to an exemplary aspect of the present disclosure includes, among other things, a fan having a plurality of blades, and a transmission is configured to drive the fan. 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 about 0.40.
1. A turbofan engine comprising:
a fan having a plurality of blades rotatable about a longitudinal axis;
a transmission configured to drive the fan; and
a first spool and a second spool, wherein:
the plurality of fan blades have a peak tip radius R T ;
the plurality of fan blades have an inboard leading edge radius R H at an inboard boundary of a flowpath;
a ratio of R H to R T is less than 0.40;
said first spool comprises:
a first pressure turbine; and
a first spool shaft coupling the first pressure turbine to the transmission;
said second spool comprises:
a second pressure turbine;
a first compressor; and
a second spool shaft coupling the second pressure turbine to the first compressor;
the engine comprises a plurality of main bearings wherein:
a first of said main bearings engages a static support and a forward hub of the second spool; and
a second of said main bearings engages the first spool shaft and the forward hub of the second spool;
the fan is a single-stage fan; and
a ring gear of the transmission is mounted to rotate with the fan as a unit.
2. The turbofan engine of claim 1 , wherein:
each fan blade of the plurality of fan blades has a leading edge and a trailing edge;
a splitter is positioned along the flowpath through the turbofan engine and having a leading rim separates a core branch of the flowpath from a bypass branch of the flowpath;
an inboard boundary of the core branch of the flowpath has a radius R II at an axial position of the splitter rim;
the inboard boundary of the core branch of the 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 branch of the flowpath to the radius R II is less than 1.2.
3. The turbofan engine of claim 1 , wherein:
each fan blade of the plurality of fan blades has a leading edge and a trailing edge;
a splitter is positioned along the flowpath through the turbofan engine and having a leading rim separates a core branch of the flowpath from a bypass branch of the flowpath;
an inboard boundary of the core branch of the flowpath has a radius R II at an axial position of the splitter rim;
the inboard boundary of the core branch of the 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 turbofan engine of claim 3 , wherein:
said ratio of the radius R I to the radius R II is 0.55-1.0.
5. The turbofan engine of claim 4 , wherein:
the plurality of fan blades are non-variable.
6. The turbofan engine of claim 5 , further comprising:
a variable fan nozzle.
7. The turbofan engine of claim 6 , wherein:
the forward hub extends forward from a disk of the first compressor.
8. The turbofan engine of claim 7 , wherein:
the forward hub extends forward from a bore of the disk of the first compressor.
9. The turbofan engine of claim 1 , wherein:
a separation of a transverse centerplane of the first bearing and a transverse centerplane of the second bearing is less than a radius (R B ) of the first bearing.
10. The turbofan engine of claim 1 , wherein:
a first seal, seals the first bearing and a second seal seals the second bearing to isolate a transmission compartment ahead of the first bearing relative to the longitudinal axis and the second bearing from a region behind the first bearing and the second bearing relative to the longitudinal axis.
11. The turbofan engine of claim 1 , wherein:
the transmission comprises:
a sun gear mounted to rotate with the first shaft;
said ring gear;
a plurality of intermediate gears between the sun gear and the ring gear; and
a carrier holding the intermediate gears.
12. The turbofan engine of claim 11 , wherein:
a third of said main bearings is a thrust bearing engaging the first spool shaft; and
a fourth of said main bearings is a non-thrust roller bearing engaging an aft end of the first spool shaft.
13. The turbofan engine of claim 1 , wherein:
said second pressure turbine is a high pressure turbine; and
said first compressor is a high pressure compressor.
14. The turbofan engine of claim 13 , wherein:
the first pressure turbine has three to five blade stages.
15. The turbofan engine of claim 14 , wherein:
the second spool shaft engages at least two of said main bearings, at least one of which is a thrust bearing.
16. The turbofan engine of claim 15 , wherein the ratio of R H to R T is less than 0.30.
17. A turbofan engine comprising:
a fan having a plurality of blades rotatable about a longitudinal axis;
a transmission configured to drive the fan; and
a first spool and a second spool, wherein:
the plurality of fan blades have a peak tip radius R T ;
the plurality of fan blades have an inboard leading edge radius R H at an inboard boundary of a flowpath;
a ratio of R H to R T is less than 0.40;
said first spool comprises:
a first pressure turbine; and
a first shaft coupling the first pressure turbine to the transmission;
said second spool comprises;
a second pressure turbine;
a first compressor; and
a second spool shaft coupling the second pressure turbine to the first compressor;
the engine comprises a plurality of main bearings wherein:
a first of said main bearings engages a static support and a forward hub of the second spool; and
a second of said main bearings engages the first shaft and the forward hub of the second spool; and
the first bearing and the second bearing are behind the transmission relative to the longitudinal axis.
18. The turbofan engine of claim 17 , wherein:
the transmission comprises:
a sun gear mounted to rotate with the first shaft;
a ring gear mounted to rotate with the fan;
a plurality of intermediate gears between the sun gear and the ring gear; and
a carrier holding the intermediate gears.
19. The turbofan engine of claim 17 , wherein:
the fan is a single-stage fan.
20. The turbofan engine of claim 17 , wherein the ratio of R H to R T is less than 0.30.
21. A turbofan engine comprising:
a fan having a plurality of blades;
a transmission configured to drive the fan; and
a first spool and a second spool, wherein:
the plurality of fan blades have a peak tip radius R T ;
the plurality of fan blades have an inboard leading edge radius R H at an inboard boundary of a flowpath;
a ratio of R H to R T is less than 0.40;
said first spool comprises:
a first pressure turbine; and
a first spool shaft coupling the first pressure turbine to the transmission;
said second spool comprises;
a second pressure turbine;
a first compressor; and
a second spool shaft coupling the second pressure turbine to the first compressor;
the first compressor has a rear hub engaging a bearing;
said bearing engages the first shaft; and
another bearing engages the first compressor and the first shaft.
22. The turbofan engine of claim 21 , wherein:
the transmission comprises:
a sun gear mounted to rotate with the first shaft;
a ring gear mounted to rotate with the fan;
a plurality of intermediate gears between the sun gear and the ring gear; and
a carrier holding the intermediate gears.
23. The turbofan engine of claim 21 , wherein:
the fan is a single-stage fan.
24. The turbofan engine of claim 23 , wherein the ratio of RH to RT is less than 0.30.