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DIY Foil Kites

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stefmoris
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DIY Foil Kites

Postby stefmoris » Sun Dec 06, 2015 1:35 am

After learning a lot from my first attempt,

link to Kiteforum Post

I decided to make two new kites, free ride for hydrofoils, in time for a trip to Baja this winter:

6.5 M2, 19 cells, 5.2 aspect ratio, 1.22 kg.

11 M2, 27 cells, 5.7 aspect ratio, 1.92 kg.

I've made many changes and what I hope will be improvements, and designed in some subtle differences between the two new ones to maximise my learning. I've reduced the cell count (maybe too much?) and added mini ribs for a clean trailing edge release. I'm also using leading edge battens on all ribs now instead of mylars. For my abilities and design goals( I'm an intermediate hydrofoiler and beginner with foil kites), I think a low cell count should work ok for me.

I'm giving my kite creations a name now, "lecca-lecca" which means lollipop in Italian. I have a day job but enjoy being out on my own creations.

I'll be at North Beach in Los Barilles the week before Christmas if any body wants to talk shop, take them for a ride (assuming they work!!), and drink a beer.

I'm looking forward to finally trying other foil kites on the trip as well.

Click on the pics to go to the high res version if you want to zoom in on the details.

:) -stef

Image

Image

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fpvSB
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Re: DIY Foil Kites

Postby fpvSB » Sun Dec 06, 2015 3:56 am

Absolutely awesome. This is something I might be able to convince my mom to make once designed :lol:

Did you end up using standard reflex instead of adding a bunch? Sadly from what I've seen, high cell counts are where it's at for foil kites. The ribs spanning from leading to trailing edge give much more structure.

Then again, I haven't spent hundreds of hours building/designing/flying/tuning these, so feel free to disregard my comments.

Very impressed with your work

foilholio
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Re: DIY Foil Kites

Postby foilholio » Sun Dec 06, 2015 4:09 am

Awesome effort. I love the huge cells with miniribs. This looks to be a really good new development in foil kites, weight is so important.

Notice your material costs are more than a complete kite from Pansh. Really shows the mark ups in our distribution system.

The construction time on the 16m at 116hours is immense. Paying a factory slave a dollar or so an hour is really going to add up. You start to understand why so many brands are scared to make/sell foils.

With the brains required to grasp this all, you could probably become a doctor. Though with some of the doctors I have met I wonder if they could grasp this :-o

ozchrisb
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Re: DIY Foil Kites

Postby ozchrisb » Sun Dec 06, 2015 5:42 am

I started a 9m 45 cell kite months ago, and I wish I'd just done 20 and dribs or 1/2 ribs or something. All those cells add up to a lot of cutting and prep, the sewing time isn't really the issue. If you're not racing you won't need them, and even if you are I think it's worth seeing if you can make a high performance low cell count kite. The savings would be huge. Well done, hope to compare kites one day ;)

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!

Postby foilholio » Sun Dec 06, 2015 7:02 am

What program did you use chris? was it hard to learn?

I see stef used Solidworks , some guys on tubelesskiteforum use Rhino.

From my limited repairing, cutting is a huge pain. A laser cutter would be a godsend for the whole kite. Taping seams is also annoying, some type of strong fast acting glue on a stick would be nice. I have tried all the craft types and they suck.

It's a pity you guys couldn't just send your designs to someone like Pansh and have them make them up! Sewing is hardly the most exciting of activities.

stefmoris
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Re: DIY Foil Kites

Postby stefmoris » Sun Dec 06, 2015 11:14 pm

Thanks everyone for the wonderful comments :)

fpvSB:
I took out some reflex in the tail for more bar pressure but made the chin/leading edge higher so there will still be an overall positive pitching moment.

Foilholio:
Yeah material costs are high, and the high IVA/VAT here in Italy does not help! But of course I just do it for the satisfaction for now so I feel like the overall value is still cheaper than a new bought kite! I'm getting faster but still can't seem to get below 40 minutes per cell (taping is 30 of those minutes). And that is a simple cell, vents are 1.5 hours for me. I actually like the paper backed seamstick tape because I can batch prep things, and then the paper backing really helps in the tricky areas like leading edges and the final trailing edge. (I pull the two sides taught with my fingers, and then pull the paper backing out.

I totally agree on the laser cutter. I bought my low budget pen plotter off ebay, with the intent of one day converting it into a laser cutting table. I've design and built my own cnc router before so I know what it will take. For me it would shave about 6 hours off the whole process, but more importantly let me work to much higher tolerances. Right now, even with some modifications I made to my plotter, I still get some material slippage every now and then. It would be another 60 hour project in itself though so not sure when I'll do it, but one day for sure.

These are tedious projects -and I certainly spend more time designing and building things, than time on the water, but
that is what the sport is for me and how I enjoy it most.

ozchrisb:
Awesome, I'd love to see your kite and compare notes. Agreed, the sewing is minor compared to all the prep, taping, and moving material around. Who knows, maybe low cell counts will show some other advantages too other than just time, weight, and material cost savings - perhaps it will park deep in the window and truck downwind. We shall see :)

kitexpert
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Re: DIY Foil Kites

Postby kitexpert » Mon Dec 07, 2015 1:18 am

Well, I'm worried about cell count/AR ratio. If cell is very wide, some nasty effects may arise. Some kind of basic rule for max cell width is the same as max airfoil height for that cell. So, front view (front projection) of the cell should look squarish. Then D-ribs are at 45 degree angle at the highest point of the cell. Too much cells is almost impossible, some russian kites have about 80.

Miniribs help some amount.

Old kites, spinnaker sails, parachutes or gliders may be a good source for cheap fabric. Ribs can be made not airtight material.

I think you should have done one kite at the time for that concept. To make two so similar - and for my judgement very risky trys - is a bit foolish. But I admire your attitude - and sometimes we all must learn hard way.

"I took out some reflex in the tail for more bar pressure but made the chin/leading edge higher so there will still be an overall positive pitching moment."

This sounds a bit too unprecise. Why don't you use real kite design program, where you can adjust profile thickness, camber and max height location freely? At what stage of the making do you mod your airfoils?

Sheeted out all foil kites have light bar pressure, sheeted in (to the limit of backstall) there is surely enough of it. For long kite trips usually too much.

"I think it's worth seeing if you can make a high performance low cell count kite." -ozchrisb
"This looks to be a really good new development in foil kites, weight is so important." -foilholio

If it was possible, it would have been done years and years ago. Low cell count bulges cells, airfoil shape is getting lost. It can also distort kite spanvise, LE <-> TE. 19 cells is adequate for low aspect kite. High cell count (high AR, high L/D) is more important than low weight for high performance kite - and Speeds, sonics, chronos etc. are already light weight kites.

D-ribs main function is to get bridle more economical, tidier and having less drag. Your (ozchrisb) 45 cell kite will have quite a huge amount bridle lines, if it does not have D-ribs. That is a bit controversial to the idea of high cell count efficient kite. Modern foilkites do not have unsupported ribs.

For my knowledge half-cell D-ribs are not used in kites nowadays. And actually FS and Pansh use H-ribs, which are a bit lighter and simpler than D-ribs.

fpvSB
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Re: DIY Foil Kites

Postby fpvSB » Mon Dec 07, 2015 3:14 am

From the other thread
stefmoris wrote:I used the sheet metal tools in Solidworks then added billow manually.
FXLR5 for analyzing the profiles (just for stagnation point and 0 lift AOA)
Lightwave for visual candy and such -stef

stefmoris
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Re: DIY Foil Kites

Postby stefmoris » Mon Dec 07, 2015 6:29 pm

Kitexpert:
All valid points.

I'll report back after my trip towards the end of December with pictures and video and we can all learn something from my low cell count, high aspect attempt. :) -stef

kitexpert
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Re: DIY Foil Kites

Postby kitexpert » Mon Dec 07, 2015 8:33 pm

I really hope those kites will work. I can see much positive, especially I like 2D shape of your kites. I think it's improved from your first kite.

And anyway, those two kites have miniribs and LE battens. How much they counter low cell count, it is hard to say. Good things of course.

All the best for your try.


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