Wing tip device

1. A wing tip device for fixing to the outboard end of a wing, the wing defining a wing plane, the wing tip device comprising:

an upper wing-like element projecting upwardly with respect to the wing plane and having a trailing edge; and

a lower wing-like element fixed with respect to the upper wing-like element and having a root chord and a trailing edge, the lower wing-like element root chord intersecting with the upper wing-like element, and the lower wing-like element projecting downwardly from the intersection,

wherein the upper wing-like element is larger than the lower wing-like element and the trailing edge the lower wing-like element is adjacent the trailing edge of the upper wing-like element at the intersection,

wherein an included angle between the upper and lower wing-like elements at the intersection is less than, or equal to, 160 degrees, and

wherein the lower wing-like element has an element planform area less than approximately 25% of the upper wing-like element planform area.

2. A wing tip device according to claim 1 , wherein an included angle between the wing plane and the lower wing-like element is at least 110 degrees.

3. A wing tip device according to claim 1 , wherein the included angle between the upper and lower wing-like elements at the intersection is at least 80 degrees.

4. A wing tip device according to claim 1 , wherein the lower wing-like element is substantially planar.

5. A wing tip device according to claim 1 , wherein the lower wing-like element is substantially non-planar.

6. A wing tip device according to claim 1 , wherein the lower wing-like element has wing twist.

7. A wing tip device according to claim 1 , wherein the lower wing-like element has a sweep back angle.

8. A wing tip device according to claim 1 , wherein the upper wing-like element includes a substantially planar portion.

9. A wing tip device according to claim 8 , wherein the upper wing-like element is substantially planar.

10. A wing tip device according to claim 8 , wherein the upper wing-like element further includes an arcuate transition portion adapted to smoothly blend the outboard end of the wing into the substantially planar portion of the upper wing-like element.

11. A wing tip device according to claim 8 , wherein the upper wing-like element further includes a non-planar curved wing tip extension adapted to smoothly blend the outboard end of the wing into the substantially planar portion of the upper wing-like element.

12. A wing tip device according to claim 1 , wherein the upper wing-like element is a substantially non-planar curved wing tip extension.

13. A wing tip device according to claim 1 , wherein the upper wing-like element has a sweep back angle.

14. A wing tip device according to claim 1 , wherein the intersection between the lower wing-like element and the upper wing-like element is at the outboard end of the wing.

15. A wing tip device according to claim 1 , wherein the intersection between the lower wing-like element and the upper wing-like element is outboard of the outboard end of the wing.

16. A wing having an outboard end and a wing tip device in accordance with claim 1 fixed to its outboard end.

17. An aircraft having a wing according to claim 16 .

18. A method of fitting, or retro-fitting, a wing tip device to a wing, the method comprising fixing a wing tip device in accordance with claim 1 to the outboard end of a wing.

19. A method of modifying a wing tip device fixed to, or for fixing to, the outboard end of a wing, the wing defining a wing plane, the existing wing tip device comprising an upper wing-like element projecting upwardly with respect to the wing plane and having a trailing edge, and the method comprising providing a lower wing-like element smaller than the upper wing-like element and having a root chord and a trailing edge, and fixing the lower wing-like element to the upper wing-like element such that: the lower wing-like element root chord intersects with the upper wing-like element, and the lower wing-like element projects downwardly from the intersection; and that the trailing edge of the lower wing-like element is adjacent the trailing edge of the upper wing-like element at the intersection; and that an included angle between the upper and lower wing-like elements at the intersection is less than, or equal to, 160 degrees, and that the lower wing-like element has an element planform area less than approximately 25% of the upper wing-like element planform area.

20. A method of operating a wing having a wing tip device fixed to the outboard end of the wing, the wing defining a wing plane, and the wing tip device comprising:

an upper wing-like element projecting upwardly with respect to the wing plane and having a trailing edge; and

a lower wing-like element fixed with respect to the upper wing-like element and having a root chord and a trailing edge, the lower wing-like element root chord intersecting with the upper wing-like element, and the lower wing-like element projecting downwardly from the intersection,

wherein the upper wing-like element is larger than the lower wing-like element and the trailing edge of the lower wing-like element is adjacent the trailing edge of the upper wing-like element at the intersection,

wherein an included angle between the upper and lower wing-like elements at the intersection is less than, or equal to, 160 degrees, and

wherein the lower wing-like element has an element planform area less than approximately 25% of the upper wing-like element planform area, and

the method comprising subjecting the wing to aerodynamic loads such that the wing shape undergoes aeroelastic deformation to a state in which wing bending causes rotation of the wing tip device about the wing root such that the tip of the lower wing-like element extends further outboard in the spanwise direction than the tip of the upper wing-like element.