Airfoil for a flying wind turbine

1. An airfoil for an airborne wind turbine comprising:

a main wing adapted for attachment to an electrically conductive tether having a first end adapted for attachment to the main wing and a second end adapted for attachment to a ground station, where a trailing edge of the main wing is formed at an intersection of a top surface and a curvilinear bottom surface of the main wing;

a trailing element positioned behind the main wing and pivotable about a pivot point positioned beneath the trailing element;

wherein a chord line of the airfoil has a length that is measured from the leading edge of the main wing to a trailing edge of the trailing element;

wherein when the main wing and trailing element are positioned in a first flying position, a slot gap exists between a trailing edge of the main wing and the leading edge of the trailing element;

wherein the main wing includes a chord line having a length measured from the leading edge of the main wing to the trailing edge of the main wing;

wherein the main wing has a maximum thickness that is 17-26% of the length of the chord line of the airfoil; and

wherein a length of the main wing extending from a point that is located at 5-11% along the length of the chord line of the airfoil to a point that is located at 40% along the length of the chord line of the airfoil has a thickness that is 90% or more of the maximum thickness of the main wing.

2. The airfoil of claim 1 , wherein when the trailing edge of the trailing element is rotated about the pivot point 30 degrees from the first flying position a slot gap exists between a trailing edge of the main wing and the leading edge of the trailing element, the slot gap having a width that is the same as the width of the slot gap when the airfoil is in the first flying position.

3. The airfoil of claim 1 , wherein when the trailing edge of the trailing element is rotated about the pivot point 40 degrees from the first flying position a slot gap exists between a trailing edge of the main wing and the leading edge of the trailing element, the slot gap having a width that is the same as the width of the slot gap when the airfoil is in the first flying position.

4. The airfoil of claim 1 , wherein the chord line of the airfoil does not intersect the trailing element, other than the trailing edge of the trailing element, when the airfoil is in the first flying position.

5. The airfoil of claim 1 , wherein the pivot point is located beneath a lower surface of the trailing element.

6. The airfoil of claim 1 , wherein the main wing has a maximum thickness that is 19-21% of the length of the chord line of the airfoil.

7. The airfoil of claim 1 , wherein a pressure distribution of the airfoil at a near-stall flight condition is such that the pressure profile expressed as C p of an upper surface of the main wing increases from the leading edge of the main wing towards a trailing edge of the main wing with a positive pressure gradient having a curved shape until it reaches a pressure recovery at a transition point, and an early pressure recovery is concave and a later pressure recovery is convex or flat; and

wherein a pressure profile expressed as C p of an upper surface and a lower surface of the trailing element has a generally triangular pressure distribution with a peak near the leading edge of the trailing element.

8. The airfoil of claim 1 , wherein a secondary thickness of the main wing at a point that is located at a position that is 43% of the length of the chord line of the main wing is 95% or more of the maximum thickness of the main wing closer to the leading edge of the main wing, and,

wherein a tertiary thickness of the main wing equidistant from the maximum thickness of the main wing as the secondary thickness is also 95% or more of the maximum thickness of the main wing.

9. The airfoil of claim 1 , wherein over 20% of the overall length of the chord line of the airfoil has a thickness that is 95% of the maximum thickness of the main wing.

10. The airfoil of claim 1 , wherein a length of the main wing extending from a point that is located at 11% along the length of the chord line of the airfoil to a point that is located at 40% along the length of the chord line of the airfoil has a thickness that is 90% or more of the maximum thickness of the main wing.

11. The airfoil of claim 1 , wherein a length of the main wing extending from a point that is located at 5% along the length of the chord line of the airfoil to a point that is located at 40% along the length of the chord line of the airfoil has a thickness that is 90% or more of the maximum thickness of the main wing.

12. An airfoil for an airborne wind turbine comprising:

a main wing adapted for attachment to an electrically conductive tether having a first end adapted for attachment to the main wing and a second end adapted for attachment to a ground station, where a trailing edge of the main wing is formed at an intersection of a top surface and a curvilinear bottom surface of the main wing;

a trailing element positioned behind the main wing and pivotable about a pivot point;

wherein a chord line of the airfoil has a length that is measured from a leading edge of the main wing to a trailing edge of the trailing element;

wherein when the main wing and trailing element are positioned in a first flying position a slot gap exists between a trailing edge of the main wing and the leading edge of the trailing element;

wherein the pivot point is located beneath a lower surface of the trailing element;

wherein the main wing has a maximum thickness that is 17-26% of the length of the chord line of the airfoil; and

wherein a length of the main wing extending from a point that is located at 5-11% along the length of the chord line of the airfoil to a point that is located at 40% along the length of the chord line of the airfoil has a thickness that is 90% or more of the maximum thickness of the main wing.

13. The airfoil of claim 12 , wherein when the trailing edge of the trailing element is rotated about the pivot point 30 degrees from the first flying position a slot gap exists between a trailing edge of the main wing and the leading edge of the trailing element, the slot gap having a width that is the same as the width of the slot gap when the airfoil is in the first flying position.

14. The airfoil of claim 12 , wherein when the trailing edge of the trailing element is rotated about the pivot point 40 degrees from the first flying position a slot gap exists between a trailing edge of the main wing and the leading edge of the trailing element, the slot gap having a width that is the same as the width of the slot gap when the airfoil is in the first flying position.

15. The airfoil of claim 12 , wherein the chord line does not intersect a portion of the trailing element, other than the trailing edge of the trailing element, when the airfoil is in the first flying position.

16. The airfoil of claim 12 , wherein a length of the main wing extending from a point that is located at 11% along the length of the chord line of the airfoil to a point that is located at 40% along the length of the chord line of the airfoil has a thickness that is 90% or more of the maximum thickness of the main wing.

17. The airfoil of claim 11 , wherein a length of the main wing extending from a point that is located at 5% along the length of the chord line of the airfoil to a point that is located at 40% along the length of the chord line of the airfoil has a thickness that is 90% or more of the maximum thickness of the main wing.