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 Post subject: Virginal foil build
PostPosted: Sun Feb 08, 2015 10:27 pm 
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Joined: Sat Aug 29, 2009 11:25 pm
Posts: 3055
Location: The Naki
Hey men,

I've made the decision to build rather than buy my first hydrofoil.

So i'll be building with no actual experience in hydrofoiling. Which means i'll be relying on your advice to build me an awesome foil.

Hit me with your advice.

I have a couple of questions to start off with.

Do you want a symetrical wing shape with no in built lift? So you use AOA to provide lift?

Or a cambered shape that has lift when on a horizontal plane?

How important is dyhedral?
I see a range of dyhedral shapes on hydrofoils. Is there any consensus on which type is best?


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 Post subject: Re: Virginal foil build
PostPosted: Sun Feb 08, 2015 11:09 pm 
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Joined: Wed Oct 16, 2002 1:00 am
Posts: 5961
Location: Denmark
A symmetrical wing will work, but no reason to choose as much worse.
If you got no computer aided way of getting a real profile, just make it flat on the bottom like a classic Clark Y, easy and will work.

Anhedral is necessary for turning ability, and will also prevent ventilation when going upwind (tilting the hydrofoil a lot to windward).
You can make it a simple upside down "V" or you can make it curved, both will work.
Dihedral is never used.

For the rear wing it does not matter, anything will work so you can just use a piece of symmetrical aluminium plate with LE and TE grinded a bit.
You need a little vertical stabilizer too..

8) PF


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 12:03 am 
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Sorry. I used the wrong terminology. I see anhedral on the front wing and dihedral on the back commonly.

No cnc here. But I do have some buddies that build RC wings all the time. I plan to probe their brains for wing building knowledge.


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 12:05 am 
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Location: The Naki
ps isn't the mast one big vertical stabalizer?


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 1:16 am 
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Yes but it's very close to the center of lift, etc so it doesn't have the same effect, no leverage..


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 5:07 am 
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Joined: Wed Jan 29, 2003 1:00 am
Posts: 114
Location: New Zealand
Dude, I'm the last person to pour cold water on the home-builder BUT I think that building a foil is a seriously complex issue. There is a ton of info out there but its hard to process all that information into a working foil. You need to get a strong mast, good wing size, profile, dihedral, anhedral, AOA of both wings, fuse length etc etc and marry them all together. With no experience you are likely to get a foil that is hard to ride because you have never ridden one and dont know what it should be like anyway. It will be a ton of work for a foil that at best you will outgrow in a couple of months. I love home-building but would seriously suggest first buying a beginner foil and learning to foil and getting to understand all the issues. THEN go and build an intermediate foil.
I'd be interested to hear what has happened to all the home-builders on this forum that have built their first foils. We dont hear a lot from them after the first flight. My guess is that they dont ride them for long. Can someone enlighten me?
However if you just like the idea of a workshop project then go to it.
Just my 2 cents worth. :)


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 7:11 am 
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Location: The Naki
Those are all completely valid statements.

You are correct. If I find it hard to ride I will not know if it is my build or if I'm unco or if that's just the learning process.

To make it worse there isn't one hydrofoil at my local and I have only ever seen one in the flesh for 5 mins.

So your right a very hard project. But I have the skill, and all the materials to build a hydrofoil in stock in my garage..... I give myself to jan 2016 to build. So there is no rush and plenty of time to learn and contemplate.

I would prefer to buy a hydrofoil first ride it then build. But locally they are $2000 nzd for a second hand unit. I simply don't have that cash lurking spare. But I can use existing materials and make one for almost no additional spend.

I've been building boards since 2000 and my last job I built fins, rudders and ailerons for a crust. So I can definitely do it.


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 7:27 am 
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Hey Plummet, go for it!

I am working on # 5,6,&7 3rd edition. They work great ! Have fun, lot's to think about and many many hours of brain candy.. enjoy. Pictures & tips available . Dirk


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 8:02 am 
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Hey Plummet. I am building one as well. got as far as a twin tip prototype which I have had in the water once till my diy foot hooks broke. the fun is designing your own and the satisfaction of it working. If you keep an eye on Trade Me you should be able to pick up something pretty cheap. an Alpine foil sold for $1125 just recently. I don't have any woodworking or fibre-glassing skills and finding out by making mistakes.


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 Post subject: Re: Virginal foil build
PostPosted: Mon Feb 09, 2015 11:17 am 
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Since you are in NZ, you may be able to get hold of a 3m metre length of these louvres made by an Australian company.

The bottom one AUS8029 is 100mm by 20.4mm. I think it could be used as a mould for the mast.
If you copy the picture and zoom it until it matches the dimensions, it gives an internal width of about 16mm. The 2015 Zeeko carbon mast has a quoted width of 13mm and is compacted carbon fibre.

The idea is that you fill the two small recesses at each end of the mould by pushing small diameter rods into them. You could then maybe use a filler to smooth the nose end of the mast mould.

If you bought 3 m of the louvre, you could cut 1.2m for the layup and split it and use one half to lay the layup on. Lay heat sealable plastic film on the split aluminium to lay the carbon fibre onto.

Then for the wet layup, use 45 degree orientation carbon cloth for wrapping the outside of the layup with maybe unidirectional carbon fiber inside that and possibly a flat polythene tube maybe 2" wide at the core. Maybe like the 2" by 500 gauge polythene lay-flat tube here.
http://www.polybags.co.uk/shop/narrow-l ... _c1014.htm
That is a definite 'maybe' as I don't know that this idea could be made to work, but the idea is that you lay up a 1.2m long carbon fibre mast with the tube in the core, then wrap the heat sealable plastic around the layup and heat seal it at the tail side of the mast.

Then slide the whole lot into the louvre with 10cm protruding at each end.
Cut away 10 cm of the polythene wrapper at each end and form them into the top plate and part of the fuselage.
Then inflate the core tube to press the layup against the louvre. It might be best to keep the same underside from the layup when sliding it into the mould, then after inflating it, turn it over to help improve the upperside. It would only be practical to use a low pressure, but it might be enough to press the layup out against the aluminium to give a more compacted part with a better surface. It might help to have drilled very tiny holes in the aluminium to help the air escape.

After it is cured, grind though each edge of the louvre and remove the aluminium.

This is just a suggestion. I don't know if it can be done or how successful it might be.
The idea is to then add the tail edge onto the mast, and build the top plate and fuselage around the existing carbon - blending them to the mast.


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