Apparatus for extracting power from fluid flow

1. An apparatus for extracting power comprising:

a track comprising first and second elongate sections, wherein the first elongate section is positioned above the second elongate section, and wherein a terminal connects the first elongate section to the second elongate section;

an airfoil comprising a suction surface and a pressure surface, wherein the airfoil is coupled to the track so that the pressure surface lies between the suction surface and the track when the airfoil is alternately coupled to the first elongate section, the second elongate section, and the terminal, wherein the airfoil is moveable in opposite directions when alternately coupled to the first elongate section and second elongate section, and wherein a distance from a start to an end of the terminal is shorter than a distance from a start to an end the first elongate section and shorter than a distance from a start to an end the second elongate section; and

a power generator to harvest power from an atmospheric wind through the movement of the airfoil.

2. The apparatus of claim 1 , further comprising a bridle system coupling at least one of the first and second elongate sections to an anchor.

3. The apparatus of claim 2 , wherein the bridle system comprises three bridles directly coupled to at least one of the first and second elongate sections.

4. The apparatus of claim 2 , wherein the bridle system distributes downwind forces caused by the airfoil on at least one of the first and second elongate sections.

5. The apparatus of claim 4 , wherein the bridle system comprises at least one selected from the group consisting of a cable-stayed bridle system, a suspension cable bridle system, a flying anchor point, and a helper pylon.

6. The apparatus of claim 1 , wherein the first elongate section is attached to the second elongate section at bridle attachment points.

7. The apparatus of claim 6 , wherein the first elongate section is rigidly attached to the second elongate section.

8. The apparatus of claim 1 , wherein the airfoil has a first roll to a horizon when the airfoil is coupled to the first elongate section and a second roll to the horizon when the airfoil is coupled to the second elongate section, and wherein the first roll is different from the second roll.

9. The apparatus of claim 1 , wherein the airfoil decelerates when the airfoil transitions from the first elongate section to the terminal, and wherein the airfoil accelerates when the airfoil transitions from the terminal to the second elongate section.

10. The apparatus of claim 1 , wherein the airfoil yaws as it travels along the terminal.

11. The apparatus of claim 1 , further comprising:

a second airfoil moveable with a greater absolute velocity on the first elongate section than an absolute velocity of the first airfoil on the terminal.

12. The apparatus of claim 1 , further comprising a corral that stores the airfoil when not coupled to the track.

13. The apparatus of claim 1 , further comprising a switch for guiding the airfoils off the track.

14. The apparatus of claim 1 , further comprising a third elongate section, and wherein the airfoil is coupled to the third elongate section.

15. A method of extracting power comprising:

providing a track comprising a first elongate section and a second elongate section lower than the first elongate section;

coupling a terminal between the first and second elongate sections, wherein a distance from a start to an end of the terminal is shorter than a distance from a start to an end the first elongate section and shorter than a distance from a start to an end the second elongate section;

coupling an airframe to the track, wherein the airframe comprises a suction surface and a pressure surface, wherein the airframe is coupled to the track so that the pressure surface lies between the suction surface and the track when the airfoil is alternately coupled to the first elongate section, the second elongate section, and the terminal; and

positioning the track so that the airframe travels crosswind to an atmospheric wind.

16. The method of claim 15 , further comprising:

attaching a bridle system to at least one of the first and second elongate sections; and

anchoring the bridle system.

17. The method of claim 16 , wherein the bridle system comprises three bridles, the method further comprising directly attaching the three bridles to at least one of the first and second elongate sections.

18. The method of claim 16 , wherein the bridle system distributes downwind forces caused by the airframe on at least one of the first and second elongate sections.

19. The method of claim 18 , wherein the bridle system comprises at least one selected from the group consisting of a cable-stayed bridle system, a suspension cable bridle system, a flying anchor point, and a helper pylon.

20. The method of claim 15 further comprising attaching the first elongate section to the second elongate section at bridle attachment points.

21. The method of claim 20 , wherein the first elongate section is rigidly attached to the second elongate section.

22. The method of claim 15 , further comprising rolling the airframe at a first angle to a horizon when the airframe is coupled to the first elongate section and rolling the airframe at a second angle to the horizon when the airframe is coupled to the second elongate section, and wherein the first angle is different from the second angle.

23. The method of claim 15 , wherein the airframe decelerates when the airframe transitions from the first elongate section to the terminal, and wherein the airframe accelerates when the airframe transitions from the terminal to the second elongate section.

24. The method of claim 15 , further comprising yawing the airframe as it travels along the terminal.

25. The method of claim 15 further comprising:

coupling a second airframe to the track, wherein the second airframe is moveable with a greater absolute velocity on the first elongate section than an absolute velocity of the first airframe on the terminal.

26. The method of claim 15 , wherein the airframe is coupled to the track so that the suction surface is facing the atmospheric wind.

27. The method of claim 15 , further comprising storing the airfoil in a corral.

28. The method of claim 15 , further guiding the airfoils off the track using a switch.

29. The method of claim 15 , further comprising coupling the airfoil to a third elongate section.