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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 14, 2014 6:23 pm 
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Wood is stronger when you drill 90 degrees to the grain. Your fuselage is ok. It is the strut or mast that you are putting the pulling force of the screws along the grain that is the weak point.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 14, 2014 6:55 pm 
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Location: Chile/Brasil
the picture does no t show very good but im using a ring on the inside or the mast.
is on the weak side but ive asked the machine man to make me a stainless 16mm rod.
I will cover the head of the mast(keel) connection with carbón and fiberglass.
i did torsión on the assembled fuselaje and it cracked under light torsión.
no Little amount carbón or fiberglass will solve that!
To little material on the sides, is 4mm of Wood on both sides of the connection.
I will step it up to 13mm its easier to do it all over again!
it will be a crossbread between a beluga whale and a hammer head sharK !!
Crossbread V2 on the way! :thumb:


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 14, 2014 8:28 pm 
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Only a water test will tell, at least it won't sink. It will be easy to retrieve if it breaks.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 14, 2014 10:34 pm 
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Location: rhode island
nice job pedro.

90% of the lift for your 69kg will be provided by the front foil.

the further you move the foil forward of the strut, the more moment you have on your mounting screws.

if you position the foil under the strut, you can use some (or all) of the same screws to attach both foil and strut to the fusilage.
that will reduce bending moments at the bottom fitting.
glassing over the holes for the barrel nuts is still good practice.
i say this from a structural perspective. the kids with riding experience will have better input regarding performance.

no worries.
-bill


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 15, 2014 3:22 am 
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fwiw I think I read on the french foil forum it's good to NOT mount the wing directly under the keel but forward instead. Mounting forward allows wing and fuselage flex in use to increase wing AOA and counter the pitching moment of the wing, good for keeping control.
On the other hand it might be easier to make one that doesn't break if the wing is not cantilevered out there...
Anyway, it's great that you are building this thing!
Best luck with the next stage.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 15, 2014 6:02 am 
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windfreak74 wrote:
i weigh 68kg
how do you calculate optimum área?


Tom Spear appears to be a leading hydrofoil expert when it comes to sailboats, and is the developer of the H105 foil profile that is widely used on Moth foils.

In this post on the boat designer forum he summarizes some of the formulas used to calculate foil size: http://www.boatdesign.net/forums/boat-d ... 13243.html.

To use these formulas to optimize a kite foil we would have to know how much power our kites can produce. Here is my guesstimate of power during a straight line fast run: kite pulls with 220N (about 50 lbs) under a 30 degree angle to the direction of travel (cos 30) while at a speed of 20 mph (9 m/s) = 220 N * 0.866 * 9 m/s = 1.7 kW. Did I get that right? Maybe I am too optimistic about the angle of the kite force during a fast upwind tack.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 15, 2014 11:28 am 
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heemskn wrote:
windfreak74 wrote:
i weigh 68kg
how do you calculate optimum área?


Tom Spear appears to be a leading hydrofoil expert when it comes to sailboats, and is the developer of the H105 foil profile that is widely used on Moth foils.

In this post on the boat designer forum he summarizes some of the formulas used to calculate foil size: http://www.boatdesign.net/forums/boat-d ... 13243.html.

To use these formulas to optimize a kite foil we would have to know how much power our kites can produce. Here is my guesstimate of power during a straight line fast run: kite pulls with 220N (about 50 lbs) under a 30 degree angle to the direction of travel (cos 30) while at a speed of 20 mph (9 m/s) = 220 N * 0.866 * 9 m/s = 1.7 kW. Did I get that right? Maybe I am too optimistic about the angle of the kite force during a fast upwind tack.


There is an interesting note at the end where he says that you can adjust the spacing so the aft foil surfs the wave produced by the front foil.
With ships, there is a bow wave and a stern wave produced and the ship's drag is less when the bow and stern waves cancel each other out the most. With horse drawn barges in canals, they could speed the horse up until the barge was 'surfing' it's own wave. So at a certain speed there could be an effect where the rear foil could benefit from the wave of the front one. Of course at anything other than that speed, there may be a loss.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 15, 2014 3:58 pm 
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Location: Chile/Brasil
Hello Bwd,
Have you started building your foil?
please post your pics!!

hello hawaiis,
great news on taking the plunge to manufacture something cool!
Can you comment when will have the honour of of see the finished product?
the koa Wood use is it similar to oak ?

Hello Bill,
thanks for the imput on the foil.
I guess this weekend i will have a stronger working prototype!
:thumb:


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 15, 2014 7:07 pm 
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Koa wood is a natural marine wood that the Hawaiians used to make the Canoe to travel the Pacific Ocean. If you are using oak, make sure to use white oak, because red oak has large open end grains that soak up water like straws.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 15, 2014 9:16 pm 
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I am still gathering data.
I could do something crude soon, or I hope better a bit later.
Too many other things to do and limited space.
I thought I would be able to start by now.
I may come up with something by summer though...


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