Airfoil assembly with spacer and tie-spar

1. An airfoil assembly comprising:

at least one airfoil that has a hollow interior;

first and second platforms between which the airfoil is disposed;

at least one tie-spar that extends along an axis through the first platform, the hollow interior of the airfoil, and the second platform, and there is a thermal expansion difference D between a thermal expansion T 1 of the tie-spar in the axial direction and a combined thermal expansion T 2 of the airfoil and the first and second platforms in the axial direction; and

a spacer portion arranged between a first end of the tie-spar and the first platform, and the spacer portion has a thermal expansion T 3 in the axial direction that is greater than the thermal expansion difference D such that the spacer portion maintains the tie-spar under tension and clamps the first and second platforms on the airfoil, wherein a second end of the tie-spar abuts the second platform.

2. The airfoil assembly as recited in claim 1 , wherein the spacer portion has an aspect ratio of length-to-width of greater than one, with the length being along the axial direction and the width being perpendicular to the axial direction.

3. The airfoil assembly as recited in claim 1 , wherein at least one of the first and second platforms extends partially in the hollow interior of the airfoil.

4. The airfoil assembly as recited in claim 1 , wherein the spacer portion includes a central through-hole, through which the tie-spar is received.

5. The airfoil assembly as recited in claim 1 , wherein the spacer portion is outboard of the first platform with respect to the hollow interior of the airfoil.

6. The airfoil assembly as recited in claim 1 , wherein the hollow interior of the airfoil has multiple cavities, and the at least one tie-spar includes multiple tie-spars that extend, respectively, through the multiple cavities.

7. The airfoil assembly as recited in claim 1 , wherein there is an annular clearance gap between an exterior of the tie-spar and an interior of the spacer portion.

8. The airfoil assembly as recited in claim 7 , wherein the exterior of the tie-spar and the interior of the spacer portion each include a thermal barrier coating.

9. The airfoil assembly as recited in claim 1 , further comprising a baffle in the hollow interior of the airfoil and through which the tie-spar extends.

10. The airfoil assembly as recited in claim 9 , wherein the baffle extends from the hollow interior of the airfoil to an attachment portion external of the hollow interior.

11. The airfoil assembly as recited in claim 1 , further comprising a clip that abuts a bearing face of the tie-spar and a surface of the spacer portion to lock the tie-spar under tension.

12. The airfoil assembly as recited in claim 1 , further comprising a classified spacer mounted on the tie-spar.

13. The airfoil assembly as recited in claim 12 , wherein the classified spacer is an end cap mounted on an end of the tie-spar.

14. The airfoil assembly as recited in claim 1 , wherein the airfoil includes a radial wall that has protruding radial arms that partially extend around one of the first and second platforms.

15. A gas turbine engine comprising:

an airfoil assembly that includes:

at least one airfoil that has a hollow interior;

first and second platforms between which the airfoil is disposed;

at least one tie-spar that extends along an axis through the first platform, the hollow interior of the airfoil, and the second platform, and there is a thermal expansion difference D between a thermal expansion T 1 of the tie-spar in the axial direction and a combined thermal expansion T 2 of the airfoil and the first and second platforms in the axial direction; and

a spacer portion arranged on the tie-spar between a first end of the tie-spar and the first platform, and the spacer portion has a thermal expansion T 3 in the axial direction that is greater than the thermal expansion difference D such that the spacer portion maintains the tie-spar under tension and clamps the first and second platforms on the airfoil, wherein a second end of the tic-spar abuts the second platform.

16. A method for making an airfoil assembly, the method comprising:

arranging at least one tie-spar to extend along an axis through a first platform, a hollow interior of an airfoil, and a second platform, there being a thermal expansion difference D between a thermal expansion T 1 of the tie-spar in the axial direction and a combined thermal expansion T 2 of the airfoil and the first and second platforms in the axial direction; and

maintaining the tie-spar under tension to clamp the first and second platforms on the airfoil by using a spacer portion arranged on the tie-spar between a first end of the tie-spar and the first platform, and the spacer portion has a thermal expansion T 3 in the axial direction that is greater than the thermal expansion difference D to maintain the tie-spar under tension and clamp the first and second platforms on the airfoil, wherein a second end of the tie-spar abuts the second platform.

17. An airfoil assembly comprising:

at least one airfoil that has a hollow interior;

first and second platforms between which the airfoil is disposed;

at least one tie-spar that extends along an axis through the first platform, the hollow interior of the airfoil, and the second platform, and there is a thermal expansion difference D between a thermal expansion T 1 of the tie-spar in the axial direction and a combined thermal expansion T 2 of the airfoil and the first and second platforms in the axial direction;

a threaded member configured to threadably mate with a threaded portion at a first end of the tie-spar to secure the tie-spar; and

at least one spacer portion arranged on the tie-spar, and the spacer portion has a thermal expansion T 3 in the axial direction that is greater than the thermal expansion difference D such that the spacer portion maintains the tie-spar under tension and clamps the first and second platforms on the airfoil.

18. The airfoil assembly of claim 17 , wherein the threaded member is a threaded end cap.

19. The airfoil assembly of claim 18 , wherein the first end of the tie-spar extends through the first platform, and further comprising a classified spacer arranged between the threaded end cap and the first platform.

20. The airfoil assembly of claim 19 , wherein the threaded end cap and the classified spacer comprise a single component.

21. The airfoil assembly of claim 18 , wherein the threaded end cap includes a recess configured to receive the threaded portion of the tie-spar, and a land surface surrounding the recess, the land surface configured to serve as a bearing surface that receives and end of the at least one spacer portion.

22. The airfoil assembly of claim 17 , wherein the threaded member is part of the first platform.