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DIY Arc Speed 5.5 from foilmaker

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Rein de Vries
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DIY Arc Speed 5.5 from foilmaker

Postby Rein de Vries » Sun Sep 08, 2019 6:18 pm

Hey!

After building a nicely flying speed 3.3 Arc a few years ago I finished the 5.5m2 version recently. I am however a bit disappointed with the flying characteristics which seem to be less good as the 3.3m2. The 5.5 has difficulty opening up and shows 'hand clapping' behaviour. Releasing the steer lines and letting it fly up and fill resolves most of this however. What happens during flight is more of an issue unfortunately. Once it gains some speed it suddenly claps out of the air by I think wind from the other side of the kite. It consequently inverts frequently which makes it hard to recover.

A lot of steering line tension seems to help a bit but I think this is actually not how it is meant to fly. Anyone any experience or idea how to deal with this? :)

http://home.kpn.nl/sieger001/freaks.nl/ ... nen_e.html

Thanks!
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kitexpert
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Re: DIY Arc Speed 5.5 from foilmaker

Postby kitexpert » Sun Sep 08, 2019 8:02 pm

I worked with arcs back in the day and your issues with your kite sound familiar. Unfortunately.

Shortly said your kite shoulder and wingtip area seem to have wrong shaped airfoil and therefore also upper and lower skins are not of correct shape. These differences can be large, in a big kite easily up to 30-50cm spanwise (at some zone).

Arcs are by far the most difficult concept of traction kites because practically only kite shape decides whether it flies or not. If shape is wrong it will be even totally unstable or have to be flied keeping back line tension high. Then it struggles between flying and back stalling. Also inflation may suffer when AoA have to be kept so high. Ideally your kite should be quite stable without back line tension at all.

So not much to do here except redesign and do it again.

BTW foilmaker is a primitive design program, not much sense to use it.

merl
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Re: DIY Arc Speed 5.5 from foilmaker

Postby merl » Sun Sep 08, 2019 8:13 pm

Try a top skin tuck. That used to fix the clapping in smaller arcs back in the day. You shorten the top skin of the cells around the shoulders one on each side. Make a diamond shape about 2/3 of the length of the cell and 4 cm wide in the centre of the cell.. Make the wide point of the diamond 1/3 from the top of the cell. Put double sided tape along one side and close it. Add tape to the outside and test it. If it works then sew it up from the inside.

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Re: DIY Arc Speed 5.5 from foilmaker

Postby kitexpert » Sun Sep 08, 2019 8:29 pm

Image

Flying ARC plan should look something like that

Rein de Vries
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Re: DIY Arc Speed 5.5 from foilmaker

Postby Rein de Vries » Mon Sep 09, 2019 5:44 pm

Thanks! Would this skin tuck technique also work to resolve the other issue I described? Perhaps applied additionally on some other region in the kite? Would like to have it flying :-)

What puzzels me mostly is that the 3.3 version does not show the issue at all! It has the same profile and design i believe.

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Re: DIY Arc Speed 5.5 from foilmaker

Postby foilholio » Mon Sep 09, 2019 11:00 pm

The top skin tuck will alter the shape of the airfoil and fix your problem, though you will likely have to do a lot of them. I do something similar but sew a strip across the width of the cell. It is usually 1 or 2 or 1.5 ripstop squares as that is easy to follow. I will taper it off to nothing when it gets to the cell wall. Flysurfer has a system of making adjustments at the top or bottom skin on the cell wall, seems to work too. Through experimenting you can place adjustments largely anywhere on the cord. I usually start in the middle then if I need more I will do more on other cells or space them out like at a quarter etc. I use them to help make kites fly straight but they also change the stability of the airfoil. They actually alter the camber of the airfoil and as such the effects of camber change are what are achieved. For me steering is more effected at the very tips and is diminished as you move more towards the center of the kite. I will place small adjustment over a few cells so the effect is more distributed. I am usually fixing a problem of the kite not being sewn correctly or having stretched or warped some how so not knowing exactly how or where the problem is and it could be spread all over the cells it is best I think to spread out small adjustments. You can do for instance a series of 1 or 2 ripstop tucks on say 6 or so cells each side all in the centers, then come back and if needed add to the rear 1/4, then front 1/4 and so on. You can fine tune adding one tuck at a time etc. Tape is quite difficult to test with, it may be better to just start adding a few tucks at a time.

Also if you look at kitexperts kite the tips have negative camber where as on yours the camber is positive. Negative camber will force the tip open, positive will collapse it, force it in.

kitexpert
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Re: DIY Arc Speed 5.5 from foilmaker

Postby kitexpert » Mon Sep 09, 2019 11:14 pm

Making skin tucks is quite crude way to adjust kite. It is easy to understand there is not much hope to expect very high performance after that kind of treatment. It makes stress points to the skins which may lead to tears and leaks if kite is really used after it, and of course it adds unnecessary seams. But if kite is bad and kiter knows what he is doing it is better than nothing.

I used tucks as a last resort for the "hopeless ones", it was somehow useful method when studying issues and trying to understand how skin shapes had to be corrected and where.

Upper skin tucks will not help lower skins, they remain ill shaped and bulge respectively. After making tucks inner ribs don't fit to skins that well any more, making again loose and tight spots here and there... Like I said, don't expect your kite look very smooth after making tucks in it.

Those old designs weren't that great: too high AR, too thin airfoils, wrong shaped airfoils, wrong shaped 2-D plan, too low cell count (too wide cells), wrong shaped airfoils in shoulder/wingtip area...

In small sizes arcs are still fun kites, big sizes are more or less obsolete.

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Re: DIY Arc Speed 5.5 from foilmaker

Postby kitexpert » Mon Sep 09, 2019 11:24 pm

The method foilholio describes above is more sophisticated than what I've thought using tucks is. If it is done carefully and in many places of the kite it won't make so bad influence to kite. However ribs are not affected and they will remain their original bad shape causing some negative effect to smoothness and performance, how much it depends. With patience and making test flights between the process no doubt kite can be improved.

Rein de Vries
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Re: DIY Arc Speed 5.5 from foilmaker

Postby Rein de Vries » Tue Sep 10, 2019 6:31 pm

Thank you all for explaining! Think i will try this. Wrt the camber, you mean the kites c shape close to the tips right? This should bent more outward, especially close to the LE i guess. When i pull the break lines the same effect is achieved i saw, and the kite flies better.🙂

merl
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Re: DIY Arc Speed 5.5 from foilmaker

Postby merl » Tue Sep 10, 2019 7:39 pm



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