Turbofan engine bearing and gearbox arrangement

1. A turbofan engine comprising:

a fan;

a fan drive gear system;

a fan shaft coupling the fan drive gear system to the fan;

a low spool comprising:

a low pressure turbine; and

a low shaft coupling the low pressure turbine to the fan drive gear system;

a core spool comprising:

a high pressure turbine;

a compressor; and

a core shaft coupling the high pressure turbine to the core spool compressor;

a first bearing engaging the fan shaft, the first bearing being a thrust bearing;

a second bearing engaging the fan shaft on an opposite side of the fan drive gear system from the first bearing, the second bearing being a roller bearing; and

a third bearing engaging the low spool shaft and the fan shaft.

2. The engine of claim 1 wherein:

the third bearing is a thrust bearing.

3. The engine of claim 1 wherein:

the first bearing is a tapered roller bearing oriented to resist at least forward movement of the fan shaft.

4. The engine of claim 1 further comprising:

a fourth bearing engaging the low shaft and a fixed frame; and

a fifth bearing engaging the low shaft and an intermediate spool shaft.

5. The engine of claim 4 , wherein:

the fourth bearing and fifth bearing are roller bearings.

6. The engine of claim 4 wherein:

the fixed frame is aft of the low pressure turbine.

7. The engine of claim 4 further comprising:

a sixth bearing engaging the intermediate spool shaft and the case;

a seventh bearing engaging the core spool shaft and the case; and

an eighth bearing engaging the core spool shaft and the case.

8. The engine of claim 7 , wherein:

the sixth bearing and seventh bearing are thrust bearings.

9. The engine of claim 1 wherein:

the low spool shaft engages the third bearing and two additional bearings.

10. The engine of claim 1 wherein:

a centerplane of the third bearing is behind a centerplane of the second bearing by a distance no more than 15% of a radius of the second bearing.

11. A turbofan engine comprising:

a fan;

a fan drive gear system having a gear carrier; and

a fan shaft coupling the fan drive gear system to the fan;

a low spool comprising:

a low pressure turbine; and

a low shaft coupling the low pressure turbine to the fan drive gear system; and

a core spool comprising:

a high pressure turbine;

a compressor;

a core shaft coupling the high pressure turbine to the core spool shaft,

wherein:

the fan shaft is mounted to rotate with the gear carrier as a unit and said unit engages a first bearing forward of the gear carrier and engages a second bearing aft of the gear carrier; and

a third bearing engaging the unit and the low shaft.

12. The engine of claim 11 wherein:

said first bearing is a tapered roller bearing oriented to resist forward movement of the unit; and

said second bearing is a roller bearing engaging the unit and a fixed case structure.

13. The engine of claim 11 , wherein:

a centerplane of the third bearing is behind a centerplane of the second bearing by a distance no more than 15% of a radius of the second bearing.

14. The engine of claim 11 , further comprising:

a fourth bearing engaging the low shaft and a fixed frame; and

a fifth bearing engaging the low shaft and an intermediate spool shaft.

15. The engine of claim 14 , wherein:

the fourth and fifth bearing are roller bearings.

16. The engine of claim 14 wherein:

the fixed frame is aft of the low pressure turbine.

17. The engine of claim 14 further comprising:

a sixth bearing engaging the intermediate spool shaft and the case;

a seventh bearing engaging the core spool shaft and the case; and

an eighth bearing engaging the core spool shaft and the case.

18. The engine of claim 17 , wherein:

the sixth bearing and seventh bearing are thrust bearings.

19. The engine of claim 11 , wherein:

the first bearing is thrust bearing and the second bearing is roller bearing.

20. A turbofan engine comprising:

a fan delivering air into a bypass duct and into a core engine;

a fan drive gear system having a gear carrier; and

a fan shaft coupling the fan drive gear system to the fan and said fan shaft mounted to rotate with said gear carrier as a unit;

the core engine including a low spool comprising:

a low pressure turbine;

a low pressure shaft having a forward end with an outer periphery coupling the low pressure turbine to the fan drive gear system at an inner periphery of a sun gear in said fan drive gear system; and

a high spool comprising:

a high pressure turbine;

a compressor; and

a high pressure shaft coupling the high pressure turbine to the compressor,

wherein:

a first bearing forward of the fan drive gear system, and supporting said fan shaft and said fan drive gear system and a second bearing aft of the fan drive gear system, and supporting the fan drive gear system.

21. The engine of claim 20 , wherein there is a flexible connection supporting said fan drive gear system relative to a static housing.

22. The engine as set forth in claim 21 , wherein said high pressure turbine having one or two stages.

23. The engine as set forth in claim 22 , wherein said low pressure turbine having three or more stages.

24. The engine as set forth in claim 23 , wherein said low pressure shaft having a spline connection to said sun gear.

25. The engine as set forth in claim 21 , wherein said low shaft has a flexible portion.

26. The engine as set forth in claim 20 , wherein said high pressure turbine having one or two stages.

27. The engine as set forth in claim 26 , wherein said low pressure shaft having a spline connection to said sun gear.

28. The engine as set forth in claim 20 , wherein said low pressure shaft having a spline connection to said sun gear.