CMC aerofoil

1. An aerofoil comprising:

first and second tubular Ceramic Metal Composite (CMC) cores extending along a longitudinal axis of the aerofoil; and

an outer CMC layer surrounding the first and second tubular CMC cores and defining an outer shape of the aerofoil having leading and trailing edges,

wherein fibres within a wall of the second tubular CMC core extend to the trailing edge of the aerofoil.

2. The aerofoil of claim 1 , comprising one or more air cooling passages connecting an inner volume of the second tubular CMC core to an external surface of the aerofoil.

3. The aerofoil of claim 2 , wherein the aerofoil comprises an inner concave external surface and an outer convex external surface, a plurality of air cooling passages connecting the inner volume of the second tubular CMC core to the inner concave external surface.

4. The aerofoil of claim 2 , wherein a plurality of air cooling passages pass through a wall of the second tubular CMC core.

5. The aerofoil of claim 2 , wherein the one or more air cooling passages are defined by one or more gaps between adjacent facing portions of the inner surface of the second tubular CMC core.

6. The aerofoil of claim 5 , comprising an insert between the adjacent facing portions of the inner surface of the second tubular CMC core.

7. The aerofoil of claim 5 , wherein a plurality of air cooling passages are defined by corrugations of the inner surface of the second tubular CMC core.

8. The aerofoil of claim 6 , wherein a plurality of air cooling passages are defined by passages within the insert.

9. The aerofoil of claim 8 , wherein the insert comprises a ceramic foam.

10. The aerofoil of claim 9 , wherein the insert comprises plenums forming the plurality of air cooling passages.

11. A method of forming a CMC aerofoil, comprising the steps of:

providing first and second tubular CMC cores;

surrounding the first and second tubular CMC cores with an outer CMC layer to define an outer shape of the aerofoil having leading and trailing edges, wherein fibres within a wall of the second tubular CMC core extend to the trailing edge of the aerofoil; and

consolidating the first and second CMC cores with the outer CMC layer to form the CMC aerofoil.

12. The method of claim 11 , comprising the step of forming one or more air cooling passages connecting an inner volume of the second tubular CMC core to an external surface of the aerofoil.

13. The method of claim 12 , wherein the aerofoil comprises an inner concave external surface and an outer convex external surface, the method comprising forming a plurality of air cooling passages connecting the inner volume of the second tubular CMC core to the inner concave external surface.

14. The method of claim 12 , comprising forming a plurality of air cooling passages passing through a wall of the second tubular CMC core.

15. The method of claim 12 , wherein the one or more air cooling passages are defined by one or more gaps between adjacent facing portions of the inner surface of the second tubular CMC core.

16. The method of claim 15 , comprising providing an insert between the adjacent facing portions of the inner surface of the second tubular CMC core.

17. The method of claim 15 , comprising forming a plurality of air cooling passages by corrugations of the inner surface of the second tubular CMC core.

18. The method of claim 16 , wherein a plurality of air cooling passages are defined by passages within the insert.

19. The method of claim 1 , wherein the insert comprises a ceramic foam.

20. The method of claim 19 , wherein the insert comprises plenums forming the plurality of air cooling passages.