Rotor blade with bonded cover

1. An airfoil comprising:

an airfoil body comprising:

a first side;

a second side opposite of the first side;

a first internal cavity extending into the first side;

a second internal cavity extending into the first side; and

a first rib extending along and between the first internal cavity and the second internal cavity;

an outer cover extending over the first internal cavity, the first rib, and the second internal cavity; and

an inner cover bonded to the outer cover and the body, the inner cover comprising a first coupling element extending along the first internal cavity in cooperative engagement with the first rib;

wherein the inner cover extends into the first internal cavity and away from the outer cover in a first portion;

wherein the inner cover extends over the first rib and adjacent to the outer cover in a second portion; and

wherein the inner cover extends into the second internal cavity and away from the outer cover in a third portion;

and wherein the inner cover further comprises a corrugated stiffener spaced from the first rib along the first internal cavity.

2. The airfoil of claim 1 , further comprising adhesive for bonding the inner cover to the airfoil body and for bonding the outer cover to the inner cover.

3. The airfoil of claim 2 , wherein the coupling element provides shear stress relief for the adhesive during operation of the airfoil.

4. The airfoil of claim 1 , wherein the airfoil body defines a first major surface of the airfoil and the outer cover defines a second major surface of the airfoil.

5. The airfoil of claim 1 , wherein the airfoil body further comprises:

a third internal cavity extending into the first side; and

a second rib extending along and between the second internal cavity and the third internal cavity;

wherein the outer cover extends over the third internal cavity and the second rib.

6. The airfoil of claim 5 , wherein the inner cover further comprises:

a second coupling element extending along the second internal cavity in cooperative engagement with the second rib.

7. The airfoil of claim 1 , wherein the first coupling element comprises a side section extending transversely to the outer cover and a lateral section extending along the outer cover, the side section in cooperative engagement with the first rib.

8. The airfoil of claim 1 , wherein the first coupling element comprises a retainer forming a mechanical coupling in cooperative engagement with an inwardly tapered side of the first rib.

9. The airfoil of claim 1 , wherein the airfoil body defines a concave surface of the airfoil and the outer cover defines a convex surface of the airfoil.

10. A blade comprising:

an airfoil body comprising:

a first side;

a second side opposite of the first side;

a first internal cavity extending into the first side, the first internal cavity having a first internal surface;

a second internal cavity extending into the first side, the second internal cavity having a second internal surface; and

a first rib extending along and between the first internal cavity and the second internal cavity;

an outer cover extending over the first internal cavity, the first rib, and the second internal cavity;

an inner cover bonded to the outer cover and the body, the inner cover including a first corrugated structure in cooperative engagement with the first rib;

a first void between the outer cover and the inner cover; and

a second void between the inner cover and the first internal surface.

11. The blade of claim 10 , wherein the first corrugated structure provides shear stress relief for an adhesive between the outer cover and the inner cover during operation of the blade.

12. The blade of claim 11 , wherein the inner cover further comprises:

a corrugated stiffener spaced from the first rib along the first internal cavity.

13. The blade of claim 10 , wherein the first corrugated structure comprises a side section extending transversely to the outer cover and a lateral section extending along the outer cover, the side section in cooperative engagement with the first rib.

14. The blade of claim 10 , wherein the airfoil body further comprises:

a third internal cavity extending into the first side; and

a second rib extending along and between the second internal cavity and the third internal cavity;

wherein the outer cover extends over the third internal cavity and the second rib.

15. A rotor blade comprising:

a forging defined along a first major surface of the rotor blade;

ribs formed in the forging, the ribs defining an internal cavity therebetween;

an inner cover adhered to the forging over the internal cavity, the inner cover being a sheet having retention elements extending along the internal cavities in mechanical engagement with the ribs wherein the inner cover enters and exits the internal cavity and occupies only a portion of the internal cavity; and

an outer cover adhered to the forging over the inner cover, the outer cover defining a second major surface of the rotor blade, opposite the first major surface of the rotor blade.

16. The rotor blade of claim 15 , wherein the retention elements comprise corrugated structures having side sections extending transversely to the inner cover in mechanical engagement with corresponding sides of the ribs.

17. The rotor blade of claim 15 , wherein the retention elements comprise hook or catch features mechanically coupled to the ribs.

18. The rotor blade of claim 15 , wherein the inner cover comprises corrugated stiffening features spaced from the ribs along the internal cavities.

19. The rotor blade of claim 15 , wherein the inner cover comprises stiffeners having side surfaces transverse to the inner cover, the side surfaces spaced from the ribs along the internal cavity.