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DIY Foil Kites

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kitexpert
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Re: DIY Foil Kites

Postby kitexpert » Sat Jul 11, 2020 8:37 pm

downunder wrote:
Sat Jul 11, 2020 3:41 am
Hi guys

Quick question, I think some sort of double sided tape is used for panels, or LEI tube. Which kind of it is it? Do I order one from extremetextil

And how is it possible that the needle is not "gunked" with a glue?

Cheers
Yes, double side tape is used and it really makes sewing easier. It is a thin layer of elastic plastic with glue on both sides and peel off strip on one side. Width is 6 to 10mm. It is quite cheap stuff.

Glue sticking to the needle can be a problem, causing drop stitches and even thread breakages. Wiping needle with oily rag or solvent helps for a while. Also keeping sewing uninterrupted and pretty fast may help. Avoiding stopping needle down may help also.

I think glue is bigger problem when repair work is done through spinnaker tape on both sides. There may be differences between sewing machines also how they tolerate it, but if needle is sticky it is not good.

kitexpert
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Re: DIY Foil Kites

Postby kitexpert » Sat Jul 11, 2020 8:44 pm

Rein de Vries wrote:
Sat Jun 13, 2020 1:53 pm
For the lower skin I made the following design. 4 rows for the bridles and also various straps on the billowed surface. I used the ideas on the latest commercial models here and there.

lowerS.png

Also applying H ribs on the center cell and 75% finger ribs on the other cells I have now quite some internal structure for stiffness of the wing. In SP it looks like this. AR ~ 6.3 using 45 cells on 5m2 flat.

HF5.png

Using the billow settings below, I expect about the right strap tension is found. Thinking about dacron band (3-4 cm) for the straps. Is this the commonly used material for it?

billow.png

My uncertainty is still mainly with the airfoil shape. I changed a bit the measured shape using the idea below to find a more positive moment as well.

adjust.png
airfoil2.png

I would expect if you know what to look at in the lift drag diagrams from Xfoil / Javafoil, one could develop the airfoil in a more educated manner. Does anyone have further insights on this? I still feel it is a rather large guess to just start with a certain shape, be it this measured and adapted shape or some known airfoil (e.g. MH91).

The top developers of this world probably use computational fluid dynamics (CFD) programs to test on the stability of their designs I would expect. My experience is that the camber is quickly to large leading to instability like front collapses. On the other hand I measured up to over 3% of camber on some very succesfull models, so it should be possible. If I use the mod as given above, the camber is reduced but the pitching moment goes up, leading to stability at the cost of lift. :roll:
This is an ambitious plan because kite type is far from easy. Having that many cells and inner parts make kite very laborious to make.

Dacron band is an overkill, straps don't have to be that strong. It is quite heavy stuff. Usually straps are of same material as ribs and diagonals.

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Schietwedder
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Re: DIY Foil Kites

Postby Schietwedder » Mon Jul 13, 2020 10:29 pm

First test today.
I'm really happy, flew out of the bag without any adjustments in the mixer just setting up the depower.

Didn't manage to frontstall it even by pulling extra on the front lines when fully depowered. Flies really far to the sides if the wind window without collapsing, gonna make some gopro footage the following days when its a bit ligther. Today it was too big for the buggy in 15 knots once gaining some apparent, everyone else was on 6-9m depower foils or 3-5m handlekites but i coukdnt wait to get it in the air of course :)))
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Re: DIY Foil Kites

Postby loco4viento » Tue Jul 14, 2020 12:19 am

I think that’s fantastic.
Great job!
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Rein de Vries
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Re: DIY Foil Kites

Postby Rein de Vries » Tue Jul 14, 2020 4:17 pm

Very much impressed! Looking forward to the gopro footage :D
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Schietwedder
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Re: DIY Foil Kites

Postby Schietwedder » Sat Jul 18, 2020 5:43 pm

Thanks for the comments, and advice on design from this thread! Especially Kitexpert who helped with bridle design.
Some more close ups,
A bit less wind, so I could test it against some PL Aero V1 and Sonic FR's.
I had some direct upwind and downwind reaching legs against a Sonic FR 15m.
The performance is really good, the sonic was faster of course but not by much.

On a 3km downwind leg the sonic gained 150m on me, and on the upwind a bit more maybe 200-300m, but I could go the same height/angles which shows that L/D should be ok.
Bearing in mind the 15m sonic race kite vs 11.6m2 DIY freeride that is a really solid kite I think.
The surface and billowing couldn't be much better the trailing edge is really sharp without mini ribs and there are no major wrinkles.

That's it for the straight line performance and optics,
for the handling and maneuvers I will give it to some kite foilers who have better kite skills than me, I'm more at home on the land and snow, just learning my first steps on the kiteboard :D
After this kite which is the 5th DIY kite and the first one which really works beyond my expectations I will make some more of the same type in different sizes in winter I guess so I have a DIY depower foilkite quiver.
The next one will be a 8.5m2- 9m2 and then maybe a 15-18m one for really light winds, but maybe I should use the time and money more efficently and go sailing instead when its so light, the 12m should work from a few knots once I learn to foil.

Videos will follow next days when I have better internet.


Best Regards,
Niklas
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kitexpert
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Re: DIY Foil Kites

Postby kitexpert » Sat Jul 18, 2020 6:23 pm

Your kite looks very good indeed! Congrats :thumb:
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Schietwedder
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Re: DIY Foil Kites

Postby Schietwedder » Mon Jul 20, 2020 1:27 pm

Here is the video of the build and first tests.



If you want to build yours too contact me at info@schietwedderunlimited.de and I see if I can help you.

Best regards, Niklas
Last edited by Schietwedder on Mon Nov 02, 2020 6:08 pm, edited 1 time in total.
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downunder
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Re: DIY Foil Kites

Postby downunder » Mon Jul 20, 2020 1:40 pm

Nice touch building the bar as well !

Congrats!
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Re: DIY Foil Kites

Postby Regis-de-giens » Tue Jul 21, 2020 11:18 pm

Bravo
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