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How safe is kite foiling?
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Post new topic   Reply to topic    Northwest Kiteboarding -> Gorge / Portland / Oregon Coast
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Since 21 Jan 2006
1979 Posts
not really an
XTreme Poster

PostTue Sep 14, 21 7:38 am     Reply with quote

Nak wrote:
tinyE wrote:
Nak wrote:
The sharp trailing edges have no value other than to cut you.

coming from someone who has spent more than a decade on foils, i can tell you this statement is NOT true. The trailing edge will be a huge cause of drag, which probably isn't very noticeable when you have a kite pulling you, but it makes a big difference in other applications!!!

So you're saying a squared 1 - 1.5 mm thick trailing edge will cause a huge increase in drag over a razor sharp trailing edge? Could you explain how you determined this as I've seen nothing to indicate this in any of the papers I've read, nor has taking the edge of my foil's trailing edges caused any noticeable increase in drag. A sharp trailing edge is certainly easy to achieve compared to other shapes, but is not the preferred trailing edge shape according to any study I've seen. The "Donaldson Trailing Edge" shape seems to hold that distinction.

I'll agree with you that a poor trailing edge shape will both cause drag and sing, but a 1mm thick squared trailing edge should not cause any noticeable increase in drag over a sharp edge. I think you'd find the drag increase difficult to measure even with the proper equipment; any miniscule advantage certainly isn't worth the hazard involved with sharp edges. As an example, look at Lift eFoils. Certainly they have spent more on engineering than most, and have considerable incentive to reduce drag in order to increase ride time. Their trailing edges are definitely not razor sharp.

TBH, I think the perception that sharp trailing edges are superior is a case of confirmation bias. Sure take a rounded trailing edge and sand it to a razor edge and you'll reduce drag. (Rounded trailing edges have horrible drag and sing as well.) But how many sports enthusiasts have actually tested different shapes in a "current tunnel" and measured the results? Fortunately, their are numerous engineering studies that have done just this.

Let me add tinyE that I'm not doubting your word or your experience. You've been an intelligent poster here and a valuable part of the community. I'm just wondering if you've actually tested a sharp edge compared to a variety of other trailing edge shapes.

i have been through the testing more than you care to know! Smile after about 8 years of sit down foiling, tuning the trailing edge was the single most beneficial thing we found you could do to your wings. that said, there is a point of diminishing returns, but it's not before it's sharp. We had completely different conditions though, and going through the wake was a huge reveal on drag and "suck down" (where the lift would completely go away and the board would seemingly stick to the water). Kiting has different conditions, so you may get away with a duller trailing edge. I'm just saying, in general, the sharper the rear of the foil, the cleaner it performed (for us sit down foilers).

there were also benefits from sharpening the leading and trailing edges of the Tbar, but we found if you got it too sharp, the foil would "hunt"....same with the leading edge of the would "hunt", or move around really quick in jerky motions

we also found that the winglets actually caused a little drag, from the vortex created behind them. Sit down foiling has gone to thicker wings with no winglets....again, totally different application and forces.... I think kiting is much different on the foils

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