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DIY Foil Kites

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Schietwedder
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Re: DIY Foil Kites

Postby Schietwedder » Wed Aug 11, 2021 10:06 am

Hi Liam,
Nice Analysis! How did you get the Kite 3d model into XFLR?

I only used 2D Profile analysis right now to get the profile polars (cm Vs alpha and smooth pressure peak at the upper skin are the most important to minimise frontal collapses and Backstalls) latter has to be done with a mix of billowed profile and flat profile though otherwise there is not really a point in analysing it. Cm Vs alpha is most important (stability)

I had a look on your profile. It is suited a handlekite with fixed bridle more and might run into a lot of frontal collapses when used as a depower wing as it has a lot of camber really far back in the wing.
I would be very surprised if it would work.

I did not do any analysis yet with your profile as I don't have much time ATM but from experience I see some big issues there using a similar profile in my first kites. They only worked with fixed bridle at a rather big AoA in order to not collapse.

If you want you can get the profile Rein and me are using which is proven in practice.

The alternation in bird body shape looks better now!

D-Ribs: No you can't choose where to put them Surfplan puts them automatically between all bridle points with a larger cell spacing than 2.
But you don't have to cut all the D-Ribs out of course when printing the patterns. Nothing will be changed with the kite shape with or without d ribs.

Best Regards
Niklas
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Liam1
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Re: DIY Foil Kites

Postby Liam1 » Wed Aug 11, 2021 10:25 am

I made the 3d model by adding wing segments in xflr, I didn't import the model so it's just a rough approximation. I did read that cm/alpha should have a negative slope for stability indeed which mine doesn’t have, current x_CoG is at about 0.91m and I can't seem to get a negative slope that goes through cm=0 by changing the placement of the wings, changing the body (I even removed it) or adding weights so I'll try adding a bit of reflex to see if that can make it stable.
I didn’t know that cm/alpha was such a big deal for kites as well because in my mind the positive lift would make sure there would be tension on the lines keeping the kite from collapsing. That may also be why the profile was said to be great for kitesurfing and would have great stability. I’ll send you an email about your profile because then I can at least compare it to the one I currently use.

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Re: DIY Foil Kites

Postby Liam1 » Tue Aug 17, 2021 9:29 pm

So I think/hope this will be the last post before I start building the kite. My main question now is if it’s possible to see the total needed material, Surfplan does give total bridle length and top and bottom skin area but I don’t see the area needed for the ribs etc, I currently just add half of the top+bottom skin but that’s just a guess so if it’s possible to get a more accurate area that would be great.

About the ripstop I currently plan to use:
Skytex, I currently plan on using the 38 gram but can get 32 for 50 cents more and 27 for another 50 cents more, I have the 38 grams selected because I heard/read the lighter fabrics were harder to work with, is the difference really that big or would it be worth it to get the lighter fabric for better performance? (7,90 euro (1.5m2) for the 38 in case anyone was wondering)

If there are other tips/tricks/pitfalls for the building process, sewing guides etc, they’re of course welcome.

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Schietwedder
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Re: DIY Foil Kites

Postby Schietwedder » Wed Aug 18, 2021 12:14 am

Hi Liam,
For my 9m I ordered a 9,5m long roll of skytex 40 hard coating for the ribs, straps and D-Ribs which was just enough.
I did not put in all the D-ribs SP suggested, only about half where it was really neccesairy for the loads.

The Skytex is pretty easy to work with no matter what weight, there´s not really a difference. It is PU coated on both sides so its not so slippery and glue sticks to it as apposed to silicone coated which would be a difficult cloth to work with.

Depends on what you want, for a super light wind kite I would use 27 but only for the upper and lower skins. For a robust kite 38. Ribs straps and d ribs should be hard coated or a heavy(stiff) fabric as they take all the load and form a rigdid frame.

Some things to know before (if you not already know)
Vents if sewn like on FLysurfer to the ribs will need some special sewing sequence because you need to work from each vent to the outside so if your kite has 5 vents you need to split it in 7 pieces which you sew together in the end
All other vents that are like socks sewn to an opening in the upper/lower skin can be sewn in without segmenting the kite too much.

Otherwise get some 6mm sticky tape to allign things every 40 cm or so with a 4cm taoe strip and use the alignment points tool for that in SP before printing patterns.

You can print patterns as overlay on A0 and go to a copyshop, its way more accurate then glueing 400 pages of a4 together.
Just lay the cloth on the pattern then, the pattern will shine through.

Use a lot of reinforcments of light dacron or insignia sailcloth tape where you think they are needed, better safe then sorry.

Think about a wide enough (4cm at least) drainage channel at the ribs in the back of the kite for the water to exit.

I would recommend doing LE Battens, you can get some 2,4mm Alucut (Round) Nylon wire from Ratioparts which works well! 15-20m will do depending on how long they are in each cell.

I always make some sketch before sewing of the sequence so I know I don´t have a brain twist.

Work as accurate and structured as you can, then you will make the least faults if you are doing ne step at atime over and over again.

@rein de vries: You got some more tips or experience from your kite you would recommend?

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Re: DIY Foil Kites

Postby ieism » Wed Aug 18, 2021 1:56 am

I like this project, you guys are awesome. I don't plan on making a kite myself but if anyone needs large format prints in Europe I can do that for you as I have a print shop in Amsterdam. No charge, just send me a Pm and we'll figure out the file format..

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Re: DIY Foil Kites

Postby Rein de Vries » Sat Aug 21, 2021 3:15 pm

Nothing to add from my side Niklas, you said it all quite thoroughly. Uh yes, one thing, the more builders the more fun! Awesome :thumb:

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Re: DIY Foil Kites

Postby Liam1 » Fri Aug 27, 2021 8:28 pm

Sorry for the late response, I sadly have bad news. I have to put the project on hold due to personal problems (Nothing too serious), I hope to continue it towards the end of the year...
Once again thanks for all the help and even though I haven't been able to actually make a kite yet, I already learned a lot!!

Best regards, Liam

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Schietwedder
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Re: DIY Foil Kites

Postby Schietwedder » Mon Sep 27, 2021 7:51 pm

Finished off the 9m, I have to say it's my favourite kite yet.
I did not change much from the 6m it's basically the same design just attachment points of A B C and D slightly different so there is more camber induced by the mixer, also relatively long C wires and 40g Skytex hard for the structure as opposed to 32g and no c wires in the 6m

The biggest difference the upwind performance. There is definitely more race kite or at least high performance freeride genes in it. Even on the twintip and surfboard I never even went close to those angles of any kites I've ridden (haven't ridden pure race kites they will be of course much better). I just find it very remarkable for the low AR of 5.1. On the downside it has have slightly less turning ability compared to the 6 (it's also 3m2 bigger of course so that will be the main reason) and a bit more weight due to the heavier structure,more reinforcements and c wires, slightly less drift because of weight mainly and it's eager to fly further forward in the WW. Kind of expectable when a kite is getting more performant that it also has some downsides. I'll greatly take the performance and boosting ability though. It already is my favourite kite so far, and I'm really happy to have completed my 6,9,11 DIY foilkite quiver.

There may or may not be a 16.5m2 AR 6.5 super light weight design and a CNC machine on its way, more info when it's available.
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Schietwedder
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Re: DIY Foil Kites

Postby Schietwedder » Mon Sep 27, 2021 8:06 pm

And a really shaky mobile phone video

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Re: DIY Foil Kites

Postby Liam1 » Tue Sep 28, 2021 9:51 am

Looks nice, how much wind was there? It sounds like a lot but looking at the kite I wouldn't say so, something like 8 knts I would expect?


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