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leading edge diameter

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crasher
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leading edge diameter

Postby crasher » Fri May 20, 2005 3:31 am

I'm not an aeronautical engineer but I used to fly airplanes before I realized that I could have a lot more fun for a lot less money kiteboarding.

My basic understanding of an inflatable kite is that it works like the wing of an airplane. In other words,the fact that the leading edge is bigger compared to the trailing edge is the reason why it can generate lift.

So my questions are:

Is my understanding correct?

And, if so, is there some point at which the leading edge becomes so small that the kite will no longer generate lift?

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Dax
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Postby Dax » Fri May 20, 2005 3:43 am

It's not just the LE tube that creates the foil of the wing, the cut of the canopy and shape of struts also create shape that gives the kite lift. This isn't just for the Hellfish, this is for any kite.

The main reason for the LE's and struts being as big as they are is to support the structure of the kite. Some may claim that giving a bigger LE would give you more lift, but ultimately its creating drag and adding a lot of extra weight.

Pretty much all the companies are advertising smaller LE's as features this year. None as small as the LE on the Hellfish though, and none without the need for a 5th line or bridles to support the thinner LE.

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Postby Best R & D » Fri May 20, 2005 6:07 am

Drag, weight, stretch and torque are main factors where we can optimize the ILE kite. Cuben fiber material allows us to achieve better results in these aspects.

Sure we need a profile and the LE needs to be bigger than the TE, but the ratio is important and all other factors of the design need to fit together.
Also we are dealing with single surface kites, so considering the bottom of the LE creates a lower surface is not really appropriate for any ILE kite. I think we can more and more see in the most ILE kites a reduced diameter in the LE.
A problematic that limits to reduce the LE diameter with a 0 -90 aligned fabric is torque/twist. Our fabric fibers are aligned to prevent that.

Dax did some good job in explaining the question


cheers from China ( QC of the Hellfish production)
Peter
kitedesign Bestkiteboarding

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Dax
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Postby Dax » Fri May 20, 2005 6:48 am

Hey good to know my armchair engineering wasn't off.

Thanks as always for coming on the forum Peter. :thumb:

crasher
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Postby crasher » Fri May 20, 2005 2:37 pm

Thank you for your replies.

I understand the benefits of reduced drag and reduced weight.

But my question is:

Is there some point at which the leading edge would become so small that the kite would no longer produce lift or is the ultimate goal to produce a kite with a leading edge diameter of almost nothing?

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Dax
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Postby Dax » Fri May 20, 2005 3:16 pm

Again, there is more to the profile of the foil than the LE tube... so theoretically if the LE tube was paper thin, the kite would still have lift. Like Peter said though, the LE will always be thicker than the TE.

What's the smallest reasonable size? Who knows... maybe the Hellfish is already there.

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Postby Mattdog » Sat May 21, 2005 6:52 am

Further,

In the low velocity regime we are operating in (compared to planes), how much does the LE diameter really make a difference in performance ?

For light wind the advantage is likely mostly less weight, rather than a smaller dia LE. For stronger winds, I guess the advantage(s) diminish.

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Postby kitebored » Sat May 21, 2005 7:51 am

The circular shape of the LE isn't the most aerodynamic. In a perfect world it would be curved like the front of a real airplane wing...

since it can't be the right shape, i imagine that the diameter would make quite a difference.


and while we're talking about a "low speed airfoil" how fast do you think a kite actually goes? I know it's nothing compared to an airplane, but i bet kites can go freeway speeds then they're crossing the window.... maybe?

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Postby sq225917 » Sat May 21, 2005 2:36 pm

i'm betting on a good day some of those 7m kites are ripping through the window at around 50mph, only for short periods of time though.

a small leading edge is an advantage for a kite, but it has to be tied into a decent foil shape. one of the issues peter had to deal with was keeping enough foiling for lift, whilst bringing everything else in line with reduced frontal area and drag.

i'd be pretty keen to see what a double skin hellfish would do.

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Postby Tom183 » Sat May 21, 2005 3:33 pm

Not sure if you've heard of C-Quads and/or NASA Power Wings - these are single-skin kites with basically NO leading edge. The C-Quad has a 1/4-inch fiberglass spar, and the NASA Power Wing is just fabric.

So you can definitely have lift without any leading edge tube.


They don't float though, and the C-Quads are WAAAYYY better than the Power Wings - having that structure in the LE definitely counts for something, no matter how thin it is...


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