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Budget low tech kite hydrofoil DIY build a long

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Benicia Wind
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Re: Budget low tech kite hydrofoil DIY build a long

Postby Benicia Wind » Wed Aug 10, 2016 4:41 pm

Denisesewa wrote:
Benicia Wind wrote:I'm new to this DIY foil obsession. My foil has a birch mast/fuse and plywood wings, it's really slow and ugly but amazingly it mostly works and is great for learning. I'm working on model 2, faster more stable good for strapless riding. You all have so much more experience in all this, maybe you could answer a few q's.
1. What do curved wings do better? I see most wings are curved but race wings seem to be flatter.
2. What happens if the mast is not stiff enough? My mast is not very stiff and I think this may be causing stalling problems but I'm not sure.
3. Does anyone have drawings or dimensions of their favorite wings they can post? Or perhaps even some old wings they want to get rid of? Be fun to play with.

Thanks all.
In my opinion the profile (airfoil shape) of the mast and wings is most important, my first masts and wings were kind of blunt which caused ventilation issues, which I think is what you mean by stalling?
I can send you paper templates of my current wings if you like,( the ones in the pictures at the top of this page) I built these flat with winglets and curved ( 2 inch drop from center to tips) , the flat wings have a different feel and I personally prefer curved ( anhedral wings ) , my rear wings have about 3/4 inch dihedral. I consider these mid aspect freestyle wings.
The following picture is the profile of my first mast ( on the right) and my current masts( left), the difference in performance is remarkable.
Mast stiffness both lengthwise and torsional have a big impact on stability at speed and in carving turns, a flexi mast delays feedback to the rider so its more difficult to keep up with minor weight adjustments.001.JPG
Aha, my mast is very blunt in the front but tapered in the back. This may be the cause of stalling or ventilation, flow separation? Not sure what you call it but it feels like someone hit the brakes. I will do some re-shaping to see if that fixes it.
Templates for you wings would be great, thanks! Although pictures with dimensions would be OK too. Is there any shape to the bottom of the wing or is it flat?

Denisesewa
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Re: Budget low tech kite hydrofoil DIY build a long

Postby Denisesewa » Wed Aug 10, 2016 5:18 pm

Wings are just flat on the bottom, the high point of the profile is indicated , front wing at the high point in the center is 7/16ths , the core starts out as 3/8ths.
rear wing high point at center is 5/16ths, core starts out as 1/4". Straight trailing edges are easier to make and work just fine, I like the looks of the curved trailing edge. these are pretty big wings and have awesome slow speed ability for freeride/waves ( which is what I want) and still reasonably fast.
I made a former from 2x4s which is what I bend the wings on,front to back the former is 8 inches, both front and rear have the same arc, just cover the former with wax paper or polypropylene and apply epoxy to the 1/8th baltic birch ply parts then just screw the thing down to the former with drywall screws, screw through strips of scrap wood to spread the force , wait till it cures and pop off the nicely curved wing. the screw holes will fill with epoxy when laminating the carbon.
007.JPG
006.JPG
004.JPG
003.JPG

plummet
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Re: Budget low tech kite hydrofoil DIY build a long

Postby plummet » Wed Aug 10, 2016 11:24 pm

Fantastic thread.

I'm 2/3's the way through my hydrofoil build and this thread has helped heaps. I'm at the point of shaping the mast and wings. If anyone has wing and mast profiles they can share i'm super keen to see them.

In particular the wind profiles.

Denisesewa
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Re: Budget low tech kite hydrofoil DIY build a long

Postby Denisesewa » Thu Aug 11, 2016 1:36 am

I dont really have a particular wing profile, been shaping RC glider wings for 20+ years so just go at it by eye, however, with these past foil and wing builds I have found that low speed glider profiles dont work as expected on hydrofoils , my wings now are very thinned out profiles with the high point of the profile much further back, to compensate for a bit less lift I build wings with more surface area, my later wings are faster, much more forgiving in pitch, and more consistant at various speeds. I also found that I prefer flat bottom with just a bit up upsweep on entry this seems to make them less pitchy as well.The aquila profile will work well if thinned by about 20% and have a finer entry. the tough part about shaping profile cores is estimating the final shape after glassing.
8649413.jpg
One other thing I have been doing is laminating the carbon bottom of the wings before shaping the profile, this allows an exposed perimeter of carbon all the way around the wings after shaping so when you laminate the top you are laminating to a carbon edge completely encasing the core, otherwise its hell to try to get the carbon to wrap around edges without ending up with a very thick entry , my first wings had exposed wood on leading and trialing edges with just epoxy as I had sanded most of the carbon off or very thin to acheive a decent profile. with the mast I alternate sides with two layers of carbon at a time, sanding each layer back to center so as to stack alternating sides on top of each other at leading and trailing edges.

Hope that makes sense?

plummet
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Re: Budget low tech kite hydrofoil DIY build a long

Postby plummet » Thu Aug 11, 2016 2:47 am

Cool that's good info.

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Re: Budget low tech kite hydrofoil DIY build a long

Postby bay surfer » Thu Aug 11, 2016 3:15 am

Denisesewa wrote:I made a former from 2x4s which is what I bend the wings on,front to back the former is 8 inches, both front and rear have the same arc, just cover the former with wax paper or polypropylene and apply epoxy to the 1/8th baltic birch ply parts then just screw the thing down to the former with drywall screws, screw through strips of scrap wood to spread the force , wait till it cures and pop off the nicely curved wing. the screw holes will fill with epoxy when laminating the carbon.
Great, like to here that others are using the screwed composite method, Now if holes are filled with Flour and epoxy I might be in heaven.

plummet
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Re: Budget low tech kite hydrofoil DIY build a long

Postby plummet » Sat Aug 13, 2016 9:58 pm

Denisesewa wrote:I dont really have a particular wing profile, been shaping RC glider wings for 20+ years so just go at it by eye, however, with these past foil and wing builds I have found that low speed glider profiles dont work as expected on hydrofoils , my wings now are very thinned out profiles with the high point of the profile much further back, to compensate for a bit less lift I build wings with more surface area, my later wings are faster, much more forgiving in pitch, and more consistant at various speeds. I also found that I prefer flat bottom with just a bit up upsweep on entry this seems to make them less pitchy as well.The aquila profile will work well if thinned by about 20% and have a finer entry. the tough part about shaping profile cores is estimating the final shape after glassing. 8649413.jpg

One other thing I have been doing is laminating the carbon bottom of the wings before shaping the profile, this allows an exposed perimeter of carbon all the way around the wings after shaping so when you laminate the top you are laminating to a carbon edge completely encasing the core, otherwise its hell to try to get the carbon to wrap around edges without ending up with a very thick entry , my first wings had exposed wood on leading and trialing edges with just epoxy as I had sanded most of the carbon off or very thin to acheive a decent profile. with the mast I alternate sides with two layers of carbon at a time, sanding each layer back to center so as to stack alternating sides on top of each other at leading and trailing edges.

Hope that makes sense?
How much extra surface area do you compensate for with this wing profile?

I'm "borrowing" moses fluente wing shape which is about 600cm2 surface area. 550mm x 135mm
MW550-960x466.jpg

Denisesewa
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Re: Budget low tech kite hydrofoil DIY build a long

Postby Denisesewa » Sat Aug 13, 2016 11:03 pm

Unfortunately its kinda trial and error, my latest wing is probably around 700 , 530 x 160 , much lower aspect than the fluente, but its what I like, what you may like will only be known after you try a bunch of different shapes, luckily, after building a few wings you will find they are the easiest parts of the foil to build.
Just go with it, it'll work.
Post up some pics, always like seeing what others are doing.

plummet
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Re: Budget low tech kite hydrofoil DIY build a long

Postby plummet » Sun Aug 14, 2016 3:25 am

Shaping. Actually shaping the wing is fun. I like it.
image.jpeg

Denisesewa
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Re: Budget low tech kite hydrofoil DIY build a long

Postby Denisesewa » Sun Aug 14, 2016 3:39 am

Looking good! Try to reduce and streamline the frontal area at the wing /fuse. I reshaped that area on one of my first foils which made a huge improvement.


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