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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 » Mon Mar 11, 2019 1:24 am

Its slowly coming together.
I first sewed together upper and lower skin for every cell. Then I connected all cells and added vents. Now i sew in all the ribs with D-Ribs and straps. I find this method really easy and accurate, I never have cloth under the sewing machine this way. I try to find a good compromise with using as less double sided tape as possible and good enough accuracy. Four cells take me around 2h with all this internal structure. A long way to go with 33 cells .. I decided to have 7 vents, 5 relatively close to the middle and 2 at the tips. Hope this will be enough. I decided to not go for the trailing edge battens for means of simplicity. But Im really happy with my leading ede reinforments, its so easy to sew around the leading edge now when sewing ribs in... They are really stiff and not much heavyer than leading edge battens due to the dyneema composite I use.
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kitexpert
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Re: DIY AR6 closed cell Quadrifoil Style

Postby kitexpert » Mon Mar 11, 2019 11:54 am

Your work is progressing well :thumb:

For accurate sewing you could or should use alignment points for example for every 10%. But if you can do it without it is fine (ends of the seams are not out of alignment). Shapes of the cells and ribs are not very difficult to sew for that kind of design.

Your method or sewing order is different to how I've used to do it. It looks efficient though, four cells in 2h is not bad at all.

Seven vents should be enough, even five would do. LE reinforcement using stiff fabric is ok, but with plastic chord it can be done easier and a bit lighter in weight. Quite often it is possible to slide chord inside seam allowance which is easiest way to do it.

Good luck

Schietwedder
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Re: DIY AR6 closed cell Quadrifoil Style

Postby Schietwedder » Fri May 10, 2019 12:21 pm

Sailmaking season hit hard, but now i could find some time and finish this kite.
Lets see how it flies next weekend. I could not test it because of strong winds this week.
If it flies well I will hand it over to some more skilled kiters than me.
It is 1.3Kg for 6m2 incl. Mixer which is quite light I think.
Mainly I wonder if AR6 and rectangular shape work well as well as if I get some information about my new profile which i want to use in a AR5 12m design mentioned earlier.
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kitexpert
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Re: DIY AR6 closed cell Quadrifoil Style

Postby kitexpert » Fri May 10, 2019 3:12 pm

That kite looks actually quite impressive in its own way :thumb: I'm quite sure it is much better try than what I did long time ago and I really hope you can get some positive feedback from it, not just negative. Anyway it is valuable to know what not to do in the future.

Interesting to see what kind of shape your kite will take in the air.

Wingtip air intakes could have been quite a lot more to the center. You could have have it on cell 5 instead but anyway it is not that critical.

A question: how much tension do you have in your span wise straps, I mean how much thinner strap is compared to a cell?

Good luck for your tests :thumb:

Schietwedder
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Re: DIY AR6 closed cell Quadrifoil Style

Postby Schietwedder » Fri May 10, 2019 4:28 pm

Hi, thanks for the feedback.
Yes I know with the tip air intakes i actually don´t know anymore why I put them there but it wont have a negative effect I think/hope. It had something to do with that the blue cloth (because it was a recycled reserve parachute which has not been used) It was so hard to sew (silicone coated and very thin) that I put vents in the orange cloth which was 41g and a lot more stiff. But could have put it on cell 4 indeed. Is there any point why most production kites have them more towards the center other than that the tip cells are comperatvely small so a vent there would not be as efficient in area, and maybe that the flow is more spanwise towards the tips than towards the center-though that should be a relatively small effect on LE.

Strap tension:
I made some material test before with the strap, so I put 20Kg on a 100mm long section of the internal strap and measured the strain (delta). It was 3mm (3%) so I think i went to that value + a millimeter safety. So under no circumstance the strap would have more strain than a 25cm wide section of the lower skin which I also tested. -> Strap takes the load always induced by the bridle.)
The lower skin is not the same width- chordwise of course with skin tension and canopy curve so I went to different strap lengths on A,B and C straps but 4% is the delta.
I then also calculated the angle of the D-Ribs and the resulting shortening of the D-Ribs so that it is in tune with strap tension which was also some millimeters. Otherwise it could have happened that the D-Ribs don´t transfer so much loads or the kite would get a bit zick-zack shaped in the air.

All these calculations are quite simple to do on a rectangular/constant canopy curve kite but get really complicated and confusing in more complex geometries, so I like this concept very much.

kitexpert
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Re: DIY AR6 closed cell Quadrifoil Style

Postby kitexpert » Fri May 10, 2019 5:04 pm

Schietwedder wrote:
Fri May 10, 2019 4:28 pm
Hi, thanks for the feedback.
Yes I know with the tip air intakes i actually don´t know anymore why I put them there but it wont have a negative effect I think/hope. It had something to do with that the blue cloth (because it was a recycled reserve parachute which has not been used) It was so hard to sew (silicone coated and very thin) that I put vents in the orange cloth which was 41g and a lot more stiff. But could have put it on cell 4 indeed. Is there any point why most production kites have them more towards the center other than that the tip cells are comperatvely small so a vent there would not be as efficient in area, and maybe that the flow is more spanwise towards the tips than towards the center-though that should be a relatively small effect on LE.

Strap tension:
I made some material test before with the strap, so I put 20Kg on a 100mm long section of the internal strap and measured the strain (delta). It was 3mm (3%) so I think i went to that value + a millimeter safety. So under no circumstance the strap would have more strain than a 25cm wide section of the lower skin which I also tested. -> Strap takes the load always induced by the bridle.)
The lower skin is not the same width- chordwise of course with skin tension and canopy curve so I went to different strap lengths on A,B and C straps but 4% is the delta.
I then also calculated the angle of the D-Ribs and the resulting shortening of the D-Ribs so that it is in tune with strap tension which was also some millimeters. Otherwise it could have happened that the D-Ribs don´t transfer so much loads or the kite would get a bit zick-zack shaped in the air.

All these calculations are quite simple to do on a rectangular/constant canopy curve kite but get really complicated and confusing in more complex geometries, so I like this concept very much.
For the bridle configuration of your kite better (or more elegant) location for wingtip air intake is cell no 5, because that is free from dribs which can even interfere how valve works. Just a detail but if you can choose why not to choose better one. But like you wrote you had your own reasons because of the fabrics you used.

Usual locations of air intakes work well, wingtips inflate without problems from quite far away located air intakes. If it is not needed it saves weight and costs to not have them closer to wingtips.

I'm afraid you didn't consider billowing of the cells in your strap length calculations. Value of 3% is very low tension, it should be perhaps twice or triple of that. But these values depend on cell width and are AFAIK quite a lot results of practical tests. Cell shape control is certainly one of the most difficult things in foil kite (and PG) design. Too long straps don't do much, fortunately there is not harm either.

Your worry with the length of dribs is in principle correct but in practice some mm deviation is insignificant. If there wasn't dribs at all there would be many cms of deformation with bridles on every three cells and your cell width, that would be easily seen and it'd have a bad effect to how kite flies.

Lower (and upper) skin shapes come from the double curvature of your wing. The more you have canopy curve and air foil camber, the more shape upper and lower skins have and more they differ from each other.

Schietwedder
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Re: DIY AR6 closed cell Quadrifoil Style

Postby Schietwedder » Sat May 11, 2019 9:56 am

Yeah makes sense with the billow, I also remember measuring the strap tension on a Jojo wings Racemaster kite which was close to the value i used. It was 2 months ago dont remember exactly anymore.
But how much dictates billow the lower skin because two positive pressures act against each other (outside and inside) it should be smaller than on the upper side.

kitexpert
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Re: DIY AR6 closed cell Quadrifoil Style

Postby kitexpert » Sat May 11, 2019 11:21 am

Schietwedder wrote:
Sat May 11, 2019 9:56 am
Yeah makes sense with the billow, I also remember measuring the strap tension on a Jojo wings Racemaster kite which was close to the value i used. It was 2 months ago dont remember exactly anymore.
But how much dictates billow the lower skin because two positive pressures act against each other (outside and inside) it should be smaller than on the upper side.
Ok, good to hear you have measured how much tension there is in some kite. And it should be remembered there have been many fully functional kites without any straps, even though straps are nowadays considered quite important.

You could measure how much your kite loses wingspan when it is inflated compared to when it just lays uninflated.

There is slight over pressure inside kite anyway, so I don't see much if at all difference between upper and lower skins in that respect. If kite has a lot of canopy curve there will be more tension spanwise, then upper skin may billow actually less, at least in some area.


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