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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Tue Oct 29, 2013 9:05 am 
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Hawaiis wrote:
Cut a piece of 1.5" Fiberspar windsurfing mast for the fuselage


sorry but, what?

that is waaay too thick.


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Tue Oct 29, 2013 10:05 am 
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Yes, a little too fat, but very strong.
I am going to use it as a test mule for the different wings,
because my Foodsaver vacuum bagging was a failure.


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Tue Oct 29, 2013 4:48 pm 
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Hawaiis wrote:
Yes, a little too fat, but very strong.
I am going to use it as a test mule for the different wings,
because my Foodsaver vacuum bagging was a failure.


Plenty of Threads on vacuum arraignments for the home builder
over on "board-builders".

Why would you use a food-saver, when a pump out of an old refrigerator
works so well, and there FREE ?

Bille wrote:
Hawaiis wrote:
...
Carafino looks like a piece of art with G10 fiberglass sheet CNC 4-12mm covered with Carbon fiber.
The shape looked more like a curved flat sheet with rounded edges than a NACA foil shape.
weight :950g vs 450g


Carafino = 950g
Yours ---- = 450g
and there approximately the same aria, but Carafino's is Twice as Thick ?

And thanks for weighing them : Bille


And now to the Heart of the mater :

You said your panel was made from Twill-weave .
Your good at researching, so tell me how you can make that same size
panel out of carbon, and have it weigh the Exact same as yours at 450g ; but
will be 20% Stiffer ;
OR
have it the same Stiffness as the one you have but Lighter ?

Bille


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Tue Oct 29, 2013 6:26 pm 
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I have never worked with fiberglass or carbon fiber before, so making from scratch is too hard a learning curve and messy. That is why I try to use premade pieces with minimum fabrication.


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Tue Oct 29, 2013 11:23 pm 
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Location: rhode island
I'm assuming that bille is suggesting that you use unidirectional fiber. this would allow you to orient fibers to better suit your structural needs.
But..you've got choices.
-A small increase in thickness will rapidly increase stiffness. ( i.e sandwich with light wt core or hollow structure)
-Laying up the composite in a press will reduce resin content compared to bagging and increase stiffness acordingly. (squish it between two flat plates)
-You could also specify a better grade of fiber and increase fiber modulus as much as 100 pct, depending on what you've got now.
I'm sure the're other ways if you care.

I'm guessing that the real benefit of the carbon for you will be reduced weight.

On a side note.
I'm surprised that you are attributing foil thickness to performance improvements.
Reduced frontal area can reduce drag if properly trimmed. (generally thin foils have less drag than thicker foils with the same camber. but the sweet spot becomes very narrow and sensitive to angle of attack)
You may find that total planar area is a better scaling parameter for drag, since skin friction is a dominant force for submerged, streamlined objects.
(Unless the foil is not trimmed. In which case, the drag will skyrocket, regardless of frontal area)
Also, comparing lift between different cambers (profiles) is more a function of planar area, as well.
In the end, i believe it's the combination of lift/drag that you are comparing.
Imo.
Just the same, I'm enjoying hearing about your efforts.
Thanks.
Bill


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Wed Oct 30, 2013 7:37 pm 
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zfennell wrote:
On a side note.
I'm surprised that you are attributing foil thickness to performance improvements.
Reduced frontal area can reduce drag if properly trimmed. (generally thin foils have less drag than thicker foils with the same camber. but the sweet spot becomes very narrow and sensitive to angle of attack)
You may find that total planar area is a better scaling parameter for drag, since skin friction is a dominant force for submerged, streamlined objects.
(Unless the foil is not trimmed. In which case, the drag will skyrocket, regardless of frontal area)
Also, comparing lift between different cambers (profiles) is more a function of planar area, as well.
In the end, i believe it's the combination of lift/drag that you are comparing.
Imo.
Just the same, I'm enjoying hearing about your efforts.
Thanks.
Bill

You are right, according to: http://en.m.wikipedia.org/wiki/Drag_(physics)
A thin foil has almost no form drag and 100% surface drag
Shape and flow Form Drag Skin friction
thin 0% 100%
foil ~10% ~90%
ball ~90% ~10%
flat 100% 0%


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Thu Nov 07, 2013 9:07 am 
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Don't leave your carbon fiber product in the hot sun.
My carbon fin was warped in the sun.
The black color really soak up the sun's heat.


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Sat Nov 09, 2013 12:56 am 
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Total weight 5.35 kg


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 Post subject: Re: DIY carbon fiber hydrofoil
PostPosted: Sat Nov 09, 2013 1:05 am 
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This bottom half weight 2.8 kg
The strut is made of solid Hawaiian Koa wood.


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