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DIY AR6 closed cell Quadrifoil Style

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Schietwedder
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Re: DIY AR6 closed cell Quadrifoil Style

Postby Schietwedder » Sat Feb 29, 2020 2:27 pm

I got some more time in the mountains on Lake Resia with some nice gentle breeze which was good for tweaking the 6m.


As you can see the kite shape and skin tension is quite good -for a diy first try proof of concept of course (very smooth surface, low billow, good internal pressure. Some creases in the tips but I dont mind.

Im very happy for the leading edge because in my previous kites it tended to collapse/fold down. I think it was a combination of wrong profile (very unstable), low internal pressure, A-lines too far forward, and no LE stiffeners in previous kites. I tried to address all 4 issues and that seems to be solved now.

But I have a question or maybe you have some ideas with the stability and wing twist.

As also can be seen in the pictures the rectangular intended shape bends quite a lot like a banana backwards in the tips. A sign of excessive drag in the tips.
And why that could be?
-Rectangular canopy shape of course to a degree but this is kind of the concept of this kite especially related to the manufacturing time so it can't be changed.
-High AoA in the tips (they never ever collapse)

The tips never collapse but so does the middle it flips quite often on the edge of the window when the breeze is gusty. I'm used to this behaviour from the high AR thin Race kites on buggys. You just brake them a little or pull the bar and it pops back.

But maybe I could add gradualy AoA in the midle of the kite and decrease it simultaneously step by step as long as the tips stay relatively stable. This could also result in not tensioning the Leading edge so much by this backwards banan shape.
If you take a high AR piece of paper, bend it like the canopy curve and then also bend it back in the tips you can see that the tension in the LE tends to flip/front stalls the LE in the middle of the Kite. Now when you fly into a lull or turbulence the pressure lift releases from the kite but the tensiom in the LE flips the kite. (To a degree also depends a lot on the profile and moment coefficent of course)

What are your thoughts on this topic?
How are other relatively high AR thin profile kites twisted? More AoA in the tips or in the midle?
What else can be done to minimize drag in the tips and increasing the depower range by means of bridle tuning?

Schietwedder
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Re: DIY AR6 closed cell Quadrifoil Style

Postby Schietwedder » Sat Feb 29, 2020 2:28 pm

Pictures on previous page
Schietwedder wrote:
Sat Feb 29, 2020 2:19 pm
Pictures of latest test

foilholio
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Re: DIY AR6 closed cell Quadrifoil Style

Postby foilholio » Sat Feb 29, 2020 4:32 pm

Most kites pull more on the tips, its a fact of the cord taper which you don't have.

kitexpert
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Re: DIY AR6 closed cell Quadrifoil Style

Postby kitexpert » Sat Feb 29, 2020 4:54 pm

Yes, some banana effect certainly can be seen. I think I warned earlier for some "monkey business" and also said it is optimistic to assume kite with that shape will have some constant AoA through the wing. When kite bends like that it really is difficult to say what AoA it has or what is the tow point/CoL because they change from the middle to the wingtips. I'm afraid there is not much to be done by bridle adjustments, but you can always try.

Kite making is not an easy hobby, but you will learn a lot and have some real success eventually.

Banana effect is best to be avoided carefully when making kites - especially if AR is higher - by using shapes and strutures which are proven in practice. However I suggest not even trying very high AR diy kites because they are so difficult, for example if airfoil is not suitable it will result a failure or very difficult to use kite.

Mid-Low AR foil kite is much easier concept and they can give quite respectful performance. There is lot of design work there to be done, much more room for different choices than in high AR kites.


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