Fan rotor support

1. A turbofan engine comprising:

an engine case, the engine case defining a centerline and a gaspath within the engine case;

a fan having a circumferential array of fan blades;

a fan case encircling the fan blades radially outboard of the engine case;

a plurality of fan case vanes extending aftward and outward from the engine case to the fan case, the fan case vanes having a characteristic sweep angle (θ 1 ) of less than 75° relative to the engine centerline;

a forward frame comprising a plurality of vanes radially across the gas path;

a shaft;

a transmission coupling the shaft to a fan shaft to drive the fan;

a stationary forward hub structure; and

a fan bearing assembly coupling the stationary forward hub structure to the fan shaft, wherein:

the stationary forward hub has a characteristic angle (θ 3 ) of 55-70° relative to the centerline;

there is only a single stage of said fan case vanes and wherein fan rotor loads are transmitted at least partially via internal bending moments in the single stage of said fan case vanes; and

in section, a line between a center of the bearing assembly and a mounting structure on the fan case does not go more than half the local chord of an airfoil of the fan case vanes ahead of the vanes at any point along the airfoil.

2. The engine of claim 1 wherein the engine bypass ratio is greater than about 4.0.

3. The engine of claim 1 wherein:

the transmission is an epicyclic transmission.

4. The engine of claim 1 wherein:

the transmission has a circumferential array of gears having a centerplane;

the fan has a front bearing and a rear bearing, the rear bearing having a centerplane; and

a distance (L 1 ) between the gear centerplane and the rear fan bearing centerplane is less than about 1.5 times an axial length (LG) of the gears of the array.

5. The engine of claim 1 wherein:

the transmission has a circumferential array of gears having a centerplane;

the fan has a bearing system including a front bearing and a rear bearing; and

a distance (L 2 ) between the gear centerplane and the center of the fan bearing system is less than about 2.5 times an axial length (L G ) of the gears of the array.

6. The engine of claim 1 wherein:

a torque box couples the fan case vanes to the forward frame.

7. The engine of claim 6 wherein:

the torque box is formed by an outboard portion of the forward frame, inboard portions of the fan case vanes, and an aft web.

8. The engine of claim 1 wherein:

the fan case vanes characteristic sweep angle (θ 1 ) is 55-70° relative to the centerline.

9. The engine of claim 1 wherein:

the forward hub structure tapers forwardly and inwardly from a mounting flange coupling the forward hub structure to the forward frame to a center of the fan bearing assembly.

10. The engine of claim 1 wherein:

an overall conical profile from the forward hub structure to the fan case passes entirely locally through the fan case vanes.

11. The engine of claim 1 wherein:

the engine has at least one compressor section, a combustor, and at least one turbine section; and

the shaft is a turbine shaft.

12. The engine of claim 11 wherein:

the at least one compressor section comprises a high pressure compressor section and a low pressure compressor section;

the at least one turbine section comprises a high pressure turbine section and a low pressure turbine section;

the shaft is a low pressure turbine shaft coupling the low pressure turbine section to the low pressure compressor section; and

a high pressure shaft couples the high pressure turbine section to the high pressure compressor section.

13. The engine of claim 1 further comprising:

a flexure structure mounted to the forward frame and coupled to the transmission to counter torque.

14. The engine of claim 1 wherein:

the fan bearing assembly is a duplex tapered roller bearing assembly and a bellows spring engages an outer race of at least one of the bearings of the duplex tapered roller bearing.

15. An aircraft comprising:

a wing;

the engine of claim 1 ; and

a pylon mounting the engine to the wing.

16. The aircraft of claim 15 wherein:

the pylon is mounted to the fan case and the engine case.

17. A turbofan engine comprising:

an engine case;

a gaspath through the engine case;

a fan having a circumferential array of fan blades;

a turbine;

a shaft coupled to the turbine;

a fan case encircling the fan blades radially outboard of the engine case;

only a single stage of fan case vanes extending aftward and outward from the engine case to the fan case, the fan case vanes having a characteristic sweep angle (θ 1 ) of less than 75° relative to the engine centerline;

a forward frame comprising a plurality of vanes radially across the gaspath;

a stationary forward hub structure;

an epicyclic transmission coupling the shaft to a fan shaft to drive the fan and having:

a star carrier;

a flange structure coupling the engine case to the star carrier and comprising:

an outboard flange mounted to the engine case;

an inboard flange spaced rearwardly of the outboard flange;

a plurality of fingers extending from the inboard flange to engage the star carrier; and

an axially compliant and radially compliant flexure between the outboard flange and the inboard flange; and

a fan bearing assembly coupling the stationary forward hub structure to the fan shaft,

wherein an overall conical profile from the forward hub structure to the fan case passes entirely locally through the fan case vanes.

18. The engine of claim 17 wherein the engine bypass ratio is greater than about 4.0.

19. A turbofan engine comprising:

an engine case, the engine case defining a centerline and a gaspath within the engine case;

a fan having a circumferential array of fan blades;

a fan case encircling the fan blades;

a shaft;

a transmission coupling the shaft to the fan to drive the fan;

a stationary forward hub structure;

a fan bearing assembly coupling the forward hub structure to a fan shaft;

a support frame coupling the fan case, the engine case, and the stationary hub and including a plurality of supports radially across the gaspath; and

only a single stage of fan case vanes extending aftward and outward from the support frame to the fan case, the fan case vanes having a characteristic sweep angle (θ 1 ) of less than 75° relative to the engine centerline,

wherein:

an overall conical profile from the forward hub structure to the fan case passes entirely locally through the fan case vanes.

20. The engine of claim 19 wherein the engine bypass ratio is greater than about 4.0.

21. The engine of claim 1 wherein, in said section, said line does not go more than 20% of the local chord of the airfoil of the fan case vanes ahead of the vanes at any point along the vanes.

22. The engine of claim 1 wherein, in said section, the line falls locally within the airfoil along the entire airfoil.

23. The engine of claim 19 wherein:

fan rotor loads are transmitted via internal bending moments in the single stage of said fan case vanes.

24. The engine of claim 1 wherein:

wherein said fan rotor loads are transmitted via internal bending moments only in the single stage of said fan case vanes.

25. The turbofan engine of claim 1 wherein:

there is only a single said circumferential array of fan blades.