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 Post subject: First carbon fiber foil build...mast layup??
PostPosted: Sun Jun 01, 2014 1:02 pm 
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Hey folks,

I am planning on building my first carbon fiber foil and would appreciate any input! I have made a plywood and glass foil which worked great but veeery flexy, and slow. Hoping to make it ‘competitive’ to keep up with other foilers at the local and maybe race.

Planning on making the mast and fuselage first ☺

The plan:
-Shape a 5mm Balsa wood core into a rough eppler 837 profile for the mast
-Shape a 25mm Balsa wood cylinder for the fuselage
-Lay them up separately then join them mortice & tennon style and secure with more carbon layers (not moulding them)
I wasn’t going to vacuum bag it ($$$$) but I saw a trick on the French forum of compressing the fibers onto the mast with 2 bits of mdf and a fitness matt which looked alright.
Also was planning on using heat shrink tape for the fuselage to compress the fibers?


My main question is how many layers should I be aiming for the mast??

Is 6 biaxial 12k and 6 unidirectional 3k (199gram) layers each side with an additional 3 biax and 3 uni layers on the top half sufficient for the mast? Would anyone care to share their layups?

Looking for around 13mm at the base and 15mm at the top of the mast.

How many layers of carbon fiber per mm usually?

Is 3 layers biax and 3 layers uni alright for the fuselage? Has anyone used carbon fiber sleaves for this before?

Also is there much advantage to curing the bits at like 50 degrees Celsius if I am using West System Epoxy (slow hardner)?


Thanks in advance, will try post pics as I go ☺


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Sun Jun 01, 2014 5:51 pm 
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I just had my friend John, who is an experienced composite builder built my first carbon hydrofoil, the strut is made of Hawaiian Koa wood. It is a marine friendly hardwood used to make Wa'a the Hawaiian Canoe that travelled the Pacific Ocean. It is now very stiff with 2 layers of carbon. It is much stiffer than the MHL lift that I use to have, which has only one layer of cosmetic carbon. If you can find Paulownia wood, it is a marine wood light as balsa or you can use hardwood and use less carbon fiber.


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Mon Jun 02, 2014 3:19 am 
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Sounds like you are on the right track with the layup, turtles.

You have to figure out the core on your own though, I think.
For details on wall thickness, it would be worth your time laying up samples and measuring thicknesses and weights yourself.
You can look up other people's results on their blogs or forums, or manufacturers' publications, and even academic papers, but in effect, you are going to be running your own experiment anyway, so you are better off getting your own data in the area of what it takes YOU to hit the benchmarks you select from others' results, or from engineering calculations.


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Mon Jun 02, 2014 2:00 pm 
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Location: rhode island
I agree,
the variations encountered from each persons building style/experience are worth 'quantifying' with some test layups.

one example worth mentioning:
try to get a better description of the material properties for the cloth and resins you are using.
"12K" and "3K" are helpful but dont really confirm important details like modulus or strength.

you may be paying a lot for something not much stronger or stiffer than glass.

west epoxy is popular and easy to find. But considering the cost of your carbon, some higher modulus resins may be justified.

i like the idea of the braided sleeve ( with appropriate properties) as a way to neatly wrap your build and provide torsional control.


have fun,
-bill


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Mon Jun 02, 2014 11:59 pm 
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Location: Tauranga, New Zealand
post cure - yes! I'm not sure about west systems and the adr expoxy I have used comes out of the moulds softish and with a post cure goes insanely stiff.

the layup i did was 45 deg on the outside layers then uni all the way through, worked well. 12mm thick (no core) but hoping to get it cnc'd back to 9mm.

try get a lot of compression on it.


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Thu Jun 05, 2014 5:54 pm 
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Location: Perth, Australia
Post curing and balsa and WS? Wouldn't bother...The WS and postcuring will just cure it faster, no other gain. And wood might shrink.


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Wed Jun 25, 2014 10:58 am 
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Hey guys,

Thanks for all your tips! Really appreciated! I have made the mast and fuselage and really happy with the results!

I ended up getting the carbon from sollercomposites and tried to get the better quality stuff. The layup:

Shaped 9mm marine plywood core
2 layers 12k twill biax (aero-grade)
4 layers 3k uni (Intermediate Modulus)
2 layers 12k twill biax (aero-grade)

I laid up both sides in one go using the technique from the french forum to compress the fibers. The first attempt (balsa core) was a disaster but the second attempt was great (lucky I ordered a bit of extra carbon). In the end I also didn't bother post curing it with heat and it seems fine.
http://kitefoil.forumactif.org/t1602-dups-foil-v3

The braided sleeves worked a treat for the fuselage! I used three layers of sleeve and three strips top and bottom of uni. I found some Dunstone Hi-Shrink tape to wrap it in which helped but left some imperfections which I need to fill.

It ended up feeling really stiff (at least as stiff as other production foils I have wobbled on the beach) but haven't tested it in the water yet. Somewhere between 12-15mm thick which is good.


THE QUESTIONS
There are a couple of imperfections/recesses which I was hoping to fill, what is best thing to use? Ive seen lots of grey "putty" used on the french forum any clue what that is?

I have sanded some parts through the top layer of epoxy through some carbon, do I need to seal that with more epoxy?

Can I paint it with enamel spray cans?

Thanks in advance!!

Some photos of the progress :)


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Wed Jun 25, 2014 7:00 pm 
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Location: rhode island
lovely.

a flex test would provide a good method to compare with others.

simple recipe for longitudinal flex test.
support both ends and suspend 50lbs in the middle.
measure:
- distance between supports,
-actual weight, and
-max deflection.

europe2 has provided similar data from his efforts and a few commercial flavors.
-bill


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 Post subject: Re: First carbon fiber foil build...mast layup??
PostPosted: Wed Jun 25, 2014 8:44 pm 
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Location: Ukraine
there is one method :
http://kitefoil.forumactif.org/t1580-me ... ion-du-mat


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