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Plywood surf foil wing

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Kevin Brooker
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Re: Plywood surf foil wing

Postby Kevin Brooker » Fri Apr 19, 2019 12:54 pm

Years ago my hobby was building Hand and Discus Lunched Gliders. These had a 1.5 meter wingspan and some as short as 750 mm. All were foam core with vac bagged carbon and kevlar skins. Cutting the cores was done with a hot-wire pulled over templates. With very few mods this can be adapted to foils for the water. The rub is I know nothing about riding a foil but the idea of building them is intriguing. The hotwire foam method allows for adapting different foils across the span; changing the platform; adding wash -in or out to change the cavitation and stall response (might be overthinking this part) and I've also contemplated the idea of variable camber to change the lift during low speed to get going and then reflex the foil to eliminate drag when going fast. This might be a solution looking for a problem. The foam core and vac bag can also be used to build masts and eliminate the need for molds. Done right and the edges are not glued together but wrapped and will not delaminate and are much more resistant to impact failures. The surface is also super smooth and ready to go into the water. Making one-offs is also fast and simple with the hotwire so for proto-typing it'd be great. The ability to replicate foils from wing to wing is also pretty solid and finding available data on foils and best use envelopes is available. Thanks for the inspiration.

tomtom
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Re: Plywood surf foil wing

Postby tomtom » Fri Apr 19, 2019 1:49 pm

"The hot wire foam method allows for adapting different foils across the span; " can you please elaborate this? many thanks!

Im only familiar with "one profile" method see photo.
Anyway HF wing needs to be much much stronger than any model glider wing and you need to use "stringers" as I beams and/or very thick like 3mm+ laminate.
So hot-wire method isn't going to be as straightforward. But you probably use some I beams to form D in gliders wings too...
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downunder
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Re: Plywood surf foil wing

Postby downunder » Fri Apr 19, 2019 2:08 pm

Hmm

For masts the hot wire is a no go. To be fair, with alu masts prices its not worth of effort.

Carbon masts are very thin, good luck with that.

Kevin Brooker
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Re: Plywood surf foil wing

Postby Kevin Brooker » Sat Apr 20, 2019 12:06 am

TomTom,
By using the drop cutter as in your photo the foil can be changed from one end to the other by using a different template on either side. if you need three adaptations re use the template of the left (for discussion) and put it onto the right end of the next block. It will match exactly and then change to the new template on the left of the second block. All sorts of spars can be built into the foam wings to keep them super stiff. The layup schedule matters too. In addition to surface to surface spars you can also cut a spanwise hole and insert a carbon tube and contact each skin. If the planform tapers the tube doesn't work too well and the spar can be built in place using Uni or just plain tow. The tow can be under tension during the cure and this increases the strength quite a bit. Does this answer the question?

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Re: Plywood surf foil wing

Postby Wbrussow » Sun Apr 28, 2019 4:06 am

I was in Lowes today, and had an idea. I say a rolls of wood veneer for a pretty inexpensive price. The large roll (24" x 99") is only 25 Canadian Pesos. I trust my CAD skills, though I don't trust my hand shaping skills. I was thinking of designing the wing in CAD, with a tried and tested airfoil shape, and then "slicing" the wing in cad corresponding to the thickness contours of the veneer. With a couple locating dowels along the centre the ply's should line up very well, and there will be a minimal amount of sanding.The could also be layed up over a flexed lexan sheet, before being vacuum bagged, producing a nice anhedral shape. You end up with a diy-plywood wing :P

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Re: Plywood surf foil wing

Postby Europ2 » Sun May 26, 2019 3:09 pm

Hey @Jyoder

I've read you have 1"thickness / 9"chord [Edit] = 11% thickness to chord ratio (TR)

1 - What is you airfoil section ?
2 - What is you top speed with this plywood wing ?
3 - Do you think 0.88 inch thick ensuring 8% TR would have been possible with good stiffness ?? (0.88" thick /9" chord [Edit] = 8%)
Last edited by Europ2 on Tue May 28, 2019 12:16 am, edited 1 time in total.

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Re: Plywood surf foil wing

Postby Jyoder » Sun May 26, 2019 5:54 pm

Europ2 wrote:
Sun May 26, 2019 3:09 pm
Hey @Jyoder

I've read you have 1"thickness / 11"chord = 11% thickness to chord ratio (TR)

1 - What is you airfoil section ?
2 - What is you top speed with this plywood wing ?
3 - Do you think 0.88 inch thick ensuring 8% TR would have been possible with good stiffness ?? (0.88" thick /11" chord = 8%)
It’s actually only 9in chord not 11in.

1. I shaped it by hand with no guide or airfoil reference, just what felt right, so I can’t help you there.
2. I have not measured my top speed but I can go faster than the local twin tippers even on a tiny kite if I push it.
3. Sure go for it. I think anything remotely wing like will work to some extent.
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Mikey
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Re: Plywood surf foil wing

Postby Mikey » Sun May 26, 2019 10:03 pm

Hi Jyoder,

did you shape the bottom?

Thanks,

Mike

Jyoder
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Re: Plywood surf foil wing

Postby Jyoder » Sun May 26, 2019 11:12 pm

Mikey wrote:
Sun May 26, 2019 10:03 pm
Hi Jyoder,

did you shape the bottom?

Thanks,

Mike
Yes just a bit at LE and TE to make it a semi-symmetrical airfoil. Mostly flat on bottom so rests flat on fuse.

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Re: Plywood surf foil wing

Postby Hpr » Mon May 27, 2019 9:57 am

Jyoder wrote:
Mon Apr 01, 2019 1:05 am
.... I glued 2 layers of already warped 1/2in plywood together and shaped with hand tools....
Does 'already warped' refer to dihedral? Or how did you get the dihedral?


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