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 Post subject: Re: Carbon Foil Build
PostPosted: Thu Feb 20, 2014 4:31 pm 
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Are these of any use?


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 Post subject: Re: Carbon Foil Build
PostPosted: Thu Feb 20, 2014 7:01 pm 
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Hawaiis wrote:
ronnie wrote:
The other way to use extrusions could be as a mould for the mast. After moulding the mast inside it, grind away each end of the extrusion and peel off the aluminium skins. You would then have to mould on the nose and tail of the mast.


They would be perfect and not need modification for bi-directional.


There have been studies on pure ellipses and I'm not sure if any of the extrusions are pure ellipses, but this study seemed to find that somewhere between 12% and 16% thickness/chord ratio seemed to give the best bi-directional performance.
Page 82 illustrates ellipses with 5%, 10%, 16%, 20% and 25% t/c ratios.
Page 80 shows 12% to have the best lift/drag ratio but in the diagram above that, it shows that 10% is prone to sudden stall, whereas 16% has smooth lift/drag as the angle of attack changes.
Its a pity they didn't do more studies between 12% and 16% t/c to find the best compromise.

https://mospace.umsystem.edu/xmlui/bits ... sequence=1


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 Post subject: Re: Carbon Foil Build
PostPosted: Thu Feb 20, 2014 7:12 pm 
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Laughingman wrote:
Are these of any use?


I think thick walled almost empty extrusions would be the best.

According to this photo name, these are 4" and 6" extrusions and if the thickness/chord ratio was about 15% and the chord was maybe 8" they would be suitable for the wing of a bi-directional foil.

For a mast, I think a 6" 10% t/c would be about right.


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 Post subject: Re: Carbon Foil Build
PostPosted: Fri Feb 21, 2014 9:16 pm 
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Location: Tauranga, New Zealand
[/quote]
If you can make 1cm x 10cm and still stiff, that would be in a world class territory.[/quote]

New Zeeko is 1cm thick, Damn bet me to it!
Similar idea, Taper the thing bigger as it gets to the top. where it is out of the water most of the time so not needed and the additional area doesn't affect it much. The arc shape is an attempt to stop ventilation

Picture attached is of the moulds, screenshot from rhino, done before Zeeko release, not copying :P
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 Post subject: Re: Carbon Foil Build
PostPosted: Sat Feb 22, 2014 8:39 pm 
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I have been checking out standard aluminium airfoil profiles in the relevant dimensions.

Some are used for solar shading systems where I think a dimension of 100x20 mm seems most promissing (http://c-sgroup.co.uk/lib/doc/general/c ... ochure.pdf). Theese profiles should be available in Denmark for 60-100 $ a meter. Only problem seems to be the the thickness og the material wich is only 1.6 mm.

Alternatively I have found some profiles used for spreader bars on yachts. But for some reason I have not been able to find any danish companies selling them.

So until now we stick to building our own in epoxy and glas/carbonfibres: https://www.facebook.com/#!/groups/dani ... lbuilders/
I will upload some pictures here as soon as our first batch is ready.

If any body succeeds to find a proper profile in the rigth dimensions please let me know on this forum.


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 Post subject: Re: Carbon Foil Build
PostPosted: Tue Oct 28, 2014 12:29 am 
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Location: Tauranga, New Zealand
Thought I might update this

The foil was rushed to a 'useable' state earlier in the year with very little sanding etc and chucked on a skimboard.
Unfortunately on its first run it hit the sand and broke the join holding the main wing to fuselage. Stayed connected by the helicoils and was brought in for some more reinforcement.

It was built to be just strong enough hoping that there would be some benefit with making it solid carbon to get slightly less frontal surface area and wetted surface area. This is why you might see patches on the fuselage where it was loaded up and checked for flex, if it was too much, more patches were applied on top.

To be finished after exams! but need to build a board now too..
Unless anyone has a relatively cheap foil board for sale?


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 Post subject: Re: Carbon Foil Build
PostPosted: Tue Oct 28, 2014 9:49 pm 
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Wow that fuselage is thin!


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