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What are little (Carbon) foils made of?

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Re: What are little (Carbon) foils made of?

Postby longwhitecloud » Sun Jul 26, 2020 4:47 am

Carbon at least 400% more expensive 300-400% more tensile modulus

Those fibres look thirsty? Ie short on resin.. hard to tell with resolution but look a bit too fluffy

These industries are full of bull$hit engineering, always have been.

Even the surf industry went through a stage of adding carbon laminates /rails to thick boards... claiming responsive flex on boards that had next to none to start with!

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Re: What are little (Carbon) foils made of?

Postby OzBungy » Sun Jul 26, 2020 8:55 am

I am repairing my J Shapes foil after crashing at speed into a rock. The core is foam but the damage didn't go all the way to the core. The leading edge is solid carbon for at least a couple of cm back.

So far all I've had to do is grind out the damaged bits and rebuild the shape with chopped carbon and epoxy. I took this as an opportunity to dig out a couple of old repairs done with epoxy paste. I'll finish it with a little bit of carbon wrapped around the edge, just because I can. A finish coat of epoxy and then paint and it'll be good for another 600 hours.

I love carbon, and my J Shapes foil in particular. It's so strong and so easy to repair. My foil hits the sandy bottom all the time. The odd chips and scratches happen from impacting stones and stuff on the bottom. The only serious damage has come from dropping the foil on the tip on the road when it was new, and the recent crash into a rock. Most repairs can be done quickly with epoxy paste. I'm doing a proper repair using carbon now just because I can.

I ride my foil almost every day. So far it's got just over 540 hours on it. I am bemused when people buy much more expensive foils from the name brands and either get some crap aluminium, or super shiny but not so good products.

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Re: What are little (Carbon) foils made of?

Postby Kamikuza » Sun Jul 26, 2020 10:50 am

grigorib wrote:
Sat Jul 25, 2020 4:25 am
What’s next - painting glass black so it looks like carbon it spraying carbon scraps like they make boats?
Why paint when you can vinyl wrap for the carbon look :D

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Re: What are little (Carbon) foils made of?

Postby fluidity » Mon Jul 27, 2020 9:40 am

My take on the carbon question.
Carbon is very stiff. It will shatter if overloaded. for the wings, it's pointless going carbon for slower wings, it's only worth it for thin speed wings as a surf wing will be much too bouyant with adequate carbon for strength.
Other options: Kevlar between the core and the outer composites. S Glass and/or basalt for the majority of the strength. combination of normal weave, unidirectional and biaxial and/or sleeve weave for anti-twist strength, especially the mast.
Specifically the mast: It's not providing lift. So carbon is useful in a mast because it allows you to have a thinner and lower drag mast due to it's strength. But on a surface layer only? It's really only cosmetic because the carbon will shatter when the glass is still flexing, suddenly you have lost your outer layer integrity in a weak spot, creating stiff/flex/stiff zones. Much better to be all glass or all carbon. If it was all glass, the bend would be spread over the length of the mast. If it was all carbon, the stiffness of other carbon would back up that of the outer layer. So in my opinion, you have failure by cosmetic appeal.

Personally I favor basalt for all but the mast and thinnest wings. It's cheap, very resilient, lower health risk to sand and it's naturally available.

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Re: What are little (Carbon) foils made of?

Postby FrederikS » Mon Jul 27, 2020 10:36 am

It looks like several mm of carbon fiber which is more than enough to get all the benefits structurally assuming a decent volume fiber fraction and suitable layup. Adding glass on top of foam could just be to ensure proper wetting of material in the interface, I think most Moses foils are made with RTM so it makes sense. It is just one fine high closure mat to cover the heavy tow UD or biaxial mats used inside, and ensure a smooth surface. Overall this is pretty much the industry standard for sporting equipment, whether the marketing is misleading is a not my field.

The failure mode looks strange for sandwich structure with this type of construction. Could be a simple manufacturing fault or accidental damage.

And aluminum does in no way have better properties when you want light and stiff / strong structures. The specific stiffness of CFRP laminates is around 100 (Young's modulus / density). Aluminum has 26. Specific strength is likewise almost 4 times higher for well made CFRP laminates. So if we assume even suboptimal laminate properties and layup most companies should be able to design and manufacture something that performs better per weight than an aluminum foil. If weight is not an issue then aluminum is good alternative, if a suitable alloy and post treatment is used.

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