Bearing for axial stiffening

1. A hub for a tail rotor system, the hub comprising:

a body configured to couple to a mast of the tail rotor system;

a trunnion disposed within the body;

first and second shafts disposed on opposite sides of the trunnion;

first and second end plates secured to the body; and

first and second end bearings, the first end bearing disposed between the first shaft and the first end plate and the second end bearing disposed between the second shaft and the second end plate.

2. The hub of claim 1 , wherein the first and second end bearings are elastomeric bearings comprising alternating layers of rubber and metal shims.

3. The hub of claim 2 , wherein the alternating layers of each of the first and second end bearings are oriented normal to an axis passing through a central axis of the first and second shafts.

4. The hub of claim 1 , wherein the first and second end plates comprise a dome and at least a portion of the first and second end bearings are disposed within the domes of the first and second end plates, respectively.

5. The hub of claim 4 , wherein each of the first and second end bearings comprise retainers that connect the first and second end bearings to the first and second end plates, respectively.

6. The hub of claim 1 , further comprising:

first and second elastomeric bearings, the first elastomeric bearing being disposed on the first shaft and the second elastomeric bearing being disposed on the second shaft; and

first and second mounting rings, the first mounting ring disposed between the first elastomeric bearing and an inner wall of the body and the second mounting ring disposed between the second elastomeric bearing and the inner wall of the body.

7. The hub of claim 6 , wherein:

the first and second end bearings each comprise a face that contacts an end of the first and second shafts, respectively; and

the faces of the first and second end bearings do not contact the first and second elastomeric bearings.

8. The hub of claim 6 , wherein the first and second shafts are frustoconical in shape and the first and second elastomeric bearings comprise alternating layers of shims that form concentric rings with the frustoconical first and second shafts, respectively.

9. The hub of claim 1 , wherein each of the first and second end bearings comprise retainers that connect the first and second end bearings to the first and second end plates, respectively.

10. A hub for a tail rotor, the hub comprising:

a body configured to couple to a mast;

a trunnion disposed within the body;

first and second shafts disposed on opposite sides of the trunnion;

first and second elastomeric bearings, the first elastomeric bearing being disposed on the first shaft and the second elastomeric bearing being disposed on the second shaft;

first and second mounting rings, the first mounting ring disposed between the first elastomeric bearing and an inner wall of the body and the second mounting ring disposed between the second elastomeric bearing and the inner wall of the body;

first and second end plates secured to the body, the first and second end plates each comprising a dome; and

first and second end bearings, the first end bearing disposed between the first shaft and the first end plate and the second end bearing disposed between the second shaft and the second end plate.

11. The hub of claim 10 , wherein the first and second end bearings are elastomeric bearings comprising alternating layers of rubber and metal shims.

12. The hub of claim 11 , wherein the alternating layers of each of the first and second end bearings are oriented normal to an axis passing through a central axis of the first and second shafts.

13. The hub of claim 10 , wherein at least a portion of the first and second end bearings are at least partially disposed within the domes of the first and second end plates, respectively.

14. The hub of claim 10 , wherein each of the first and second end bearings comprise retainers that connect the first and second end bearings to the first and second end plates, respectively.

15. The hub of claim 10 , wherein:

the first and second end bearings each comprise a face that contacts an end of the first and second shafts, respectively; and

the faces of the first and second end bearings do not contact the first and second elastomeric bearings.

16. The hub of claim 10 , wherein the first and second shafts are frustoconical in shape and the first and second elastomeric bearings comprise alternating layers of shims that form concentric rings with the frustoconical first and second shafts, respectively.

17. A method of improving a rotor system, the method comprising:

providing a body configured to couple to a mast of the rotor system;

placing a trunnion within the body, the trunnion comprising first and second shafts;

placing first and second elastomeric bearings on the first and second shafts, respectively;

placing first and second end bearings adjacent to the first and second shafts; and

securing first and second end plates to the body so that the first and second end bearings are disposed between the first and second end plates the first and second shafts, respectively;

wherein the first and second end bearings adjust a spring rate of the rotor system along a central axis passing through centers of the first and second elastomeric bearings to move a natural frequency of the rotor system along the central axis away from a fundamental natural frequency of the rotor system.

18. The method of claim 17 , wherein each end bearing of the first and second end bearings comprises a retainer that connects each end bearing to one end plate of the first and second end plates.

19. The method of claim 17 , wherein:

each end bearing of the first and second end bearings comprises a face that contacts one shaft of the first and second shafts; and

the faces of the first and second end bearings do not contact the first and second elastomeric bearings.

20. The method of claim 17 , wherein each end plate of the first and second end plates comprises a dome that houses at least a portion of the first and second end bearings, respectively.