Composite airfoil

1. An airfoil comprising:

a first ceramic matrix composite core with a first Young's Modulus; and

an outer section comprising a second ceramic matrix composite, at least partially surrounding the core with a second Young's Modulus, wherein the first Young's Modulus is higher than the second Young's Modulus;

wherein the first ceramic matrix composite core comprises first fibers configured to preferentially reinforce a span of the airfoil along a longitudinal axis between a root and a tip;

wherein the outer section comprises a plurality of two-dimensional plies comprising second fibers; and

wherein a Young's Modulus of the first fibers is higher than a Young's Modulus of the second fibers along the span of the airfoil.

2. The airfoil of claim 1 , further comprising an additional section between the core and the outer section, the additional section comprising third fibers, wherein a Young's Modulus of the additional fibers is lower than the Young's Modulus of the first fibers along the span and higher than the Young's modulus of the second fibers along the span.

3. The airfoil of claim 1 , wherein the first fibers in the core include a three-dimensional woven core, a unidirectional weave, a plurality of two-dimensional woven fabric plies, or a combination thereof.

4. The airfoil of claim 1 , wherein the core is molded.

5. The airfoil of claim 1 , wherein an outer surface of the outer section defines a leading edge, a trailing edge, a suction side and a pressure side of the airfoil.

6. The airfoil of claim 1 , wherein the airfoil is turbine blade or vane configured for installation in a hot section of the gas turbine engine downstream of a combustor.

7. A method of forming a composite airfoil, the method comprising:

forming a core comprising a first ceramic matrix composite with a first Young's Modulus along a span of the airfoil along a longitudinal axis between a root and a tip;

forming an outer section comprising a second ceramic matrix composite, with a second Young's Modulus along the span of the airfoil; and

joining the core with the outer section so that the core is surrounded by the outer section, wherein the first Young's Modulus is higher than the second Young's Modulus.

wherein the ceramic matrix composite core comprises first fibers configured to preferentially reinforce the span of the airfoil;

wherein the outer section comprises a plurality of two-dimensional plies comprising second fibers; and

wherein a Young's Modulus of the first fibers is higher than a Young's Modulus of the second fibers along the span of the airfoil.

8. The method of claim 7 , wherein the step of forming the core comprises:

forming the core through one of: a plurality of two-dimensional plies formed with first fibers, a mold of a plurality of first fibers and a three-dimensional weave of first fibers.

9. The method of claim 8 , wherein the first fibers in the plurality of first plies are substantially unidirectional.

10. The method of claim 8 , wherein the step of forming the outer section comprises:

forming a plurality of plies with second fibers.

11. The method of claim 10 , wherein a Young's Modulus of the first fibers is higher than a Young's Modulus of the second fibers.

12. The method of claim 7 , wherein the outer section forms a pressure side, suction side, leading edge and trailing edge of the airfoil.

13. The airfoil of claim 7 , further comprising:

forming at least one additional section comprising at least a third ceramic matrix composite, the at least one additional section comprising at least third fibers configured to preferentially reinforce the span, wherein a Young's Modulus of the at least third fibers along the span is lower than the Young's Modulus of the first fibers along the span and higher than the Young's modulus of the second fibers along the span; and

joining the at least one additional section between the core and the outer section.