There is a hybrid soft-wing concept-space between a full parafoil, and a single-skin kite; based on Kline-Fogelman (KF) airfoils, which incorporate backward-facing steps. Its been gradually confirmed, despite skeptics, that select versions do in fact enhance performance (RC modelers have not doubted). A particular KF variant of interest to kite wing design, the KFm-1, has a section like a conventional foil, but with a step mid-chord, on the underside.

To make such a wing, select a high AR COTS parafoil and add a single-skin aft "skirt" to extend the TE, doubling the area. Rig new D-lines to the new TE. The neatest way to increase angle of attack is to draw the TE center down into a sort of keel, with the wingtips remaining relatively washed-out; otherwise, a scalloped edge results.

The KF Soft Kite may be a superior trade-off, a synergism even, between the luff-resistant double-skin parafoil against the lighter, simpler, cheaper single-skin wing.

• CC BY NC SA         ~Dave Santos         28June2013              AirborneWindEnergy/message/9468

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• Terms and aspects:   
• Related links and concepts:
  • KFm-1 performance is well reported in this linked master's thesis Enhancing the aerodynamic performance of stepped airfoils by Ranganadhan Voona, 2012.   [PDF document]
  • Kline Fogleman airfoils
  • KFm
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• Commentary is welcome:
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