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 Post subject: Foil design details
PostPosted: Wed Oct 02, 2013 7:20 pm 
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I'm in the process of designing a home built foil and was hoping those with more exposure would be able to help out a bit.

There are no foils nearby to examine, and I'm curious as to what foil section, chord length, aspect ratio, area, AOA, etc have proven to be most successful. Additionally, is there a consensus behind the foil anhedral and tip turn up/down?

Any chance someone has a high aspect production foil they could measure?

Thanks!


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 Post subject: Re: Foil design details
PostPosted: Wed Oct 02, 2013 8:53 pm 
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I think this would make a very good foil, I just couldn't read those dimensions.


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 Post subject: Re: Foil design details
PostPosted: Wed Oct 02, 2013 8:59 pm 
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FYI the dimensions are in mm... click on the picture and hit ctrl + and adjust size to something you can see.


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 Post subject: Re: Foil design details
PostPosted: Wed Oct 02, 2013 9:30 pm 
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I did, and I still can not make out half of the numbers. If you will be kind enough to post them?


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 Post subject: Re: Foil design details
PostPosted: Wed Oct 02, 2013 10:51 pm 
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I'll remake a crude drawing you can reference tomorrow time permitting. I will eventually design my own based on this drawing I will likely share here once completed. Hopefully I can get some input from those who know stuff I don't... Like everything..:)


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 Post subject: Re: Foil design details
PostPosted: Thu Oct 03, 2013 12:08 am 
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I think the front wing looks like 565mm, the rear wing is 4something, just couldn't make it out.


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 Post subject: Re: Foil design details
PostPosted: Thu Oct 03, 2013 2:31 pm 
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Thanks everyone.

Has anyone doing a home build had the chance to measure one of the high aspect production foils - Sword, Spotz etc?

I'm specifically interested in the foil section. Are they symmetrical or asymmetric?

My understanding of the anhedral is that it is more unstable, but reduces the risk of tip ventilation when the foil nears the surface. Has anyone played around with a dynamic main foil (through flaps or deformation), rather than changing the AOA of the whole platform to control ride height?


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 Post subject: Re: Foil design details
PostPosted: Thu Oct 03, 2013 5:34 pm 
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tburd wrote:
Thanks everyone.

...

My understanding of the anhedral is that it is more unstable, but reduces the risk of tip ventilation when the foil nears the surface.

Has anyone played around with a dynamic main foil (through flaps or deformation), rather than changing the AOA of the whole platform to control ride height?


On the Flap thing ,these guys have, however i know from flying my
Rigid wing that every time i add Flap the glide/ratio gets Bad .

http://www.fastacraft.com/moulded_foils.html

Run through these images of hydroptere sailboat, and you will see
how they delt with the problem of ventilation since part of there foil
is Always above water :
https://www.google.com/search?q=hydropt ... l&tbm=isch

Bille


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 Post subject: Re: Foil design details
PostPosted: Thu Oct 03, 2013 11:43 pm 
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The foil section is NOT symmetrical.

Just like an airplane is never symmetrical - it will never be very performing if it was :(

So the front foils are cambered, maybe just sligthly if high speed race foils, or a lot if low speed freeride foils.

And the thickness can also vary a lot.

A thin profile is faster of course, but needs more speed to lift, and can suck air down and "stall" much easier, so a lot more sensitive to errors.

The foils are not "plain straight" either - most have changing AOA out during the foil section (wash out), just like airplanes, for stability and agility.

A lot of variables, and I actually understand why the prices are like they are - quite reasonable it seems :wink:

8) Peter


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 Post subject: Re: Foil design details
PostPosted: Fri Oct 04, 2013 11:34 am 
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Peter_Frank wrote:
Just like an airplane is never symmetrical - it will never be very performing if it was :(

think some they are - those acrobatic airplanes that need to fly inverted :P

Peter_Frank wrote:
The foils are not "plain straight" either - most have changing AOA out during the foil section (wash out), just like airplanes, for stability and agility.

from memory wash out main purpose is to control lif distribution across the span to reduce drag - the closer the lift distribution is to an elipse the lower induced drag you will have

for the same effect maybe it´s just easier to start with a wing with an eliptic shape platform, think spitfire, instead of choosing a different shape and then having to play with the AoA along the span (something that would require a CFD program to know what one would be doing..)


NACA has numerous foils optimized to operate at certain Reynolds (function of velocity and viscosity if I remenber right), but I do not know enough to just go there and pick 1 that would make sense for you guys


Think we need Spork jumping into this topic..


Last edited by Tiago1973 on Fri Oct 04, 2013 8:54 pm, edited 1 time in total.

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