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Wing profile info for backyard hydrofoil builders

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salvatoreone
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Re: Wing profile info for backyard hydrofoil builders

Postby salvatoreone » Sat Oct 17, 2020 11:02 pm

Okay... So this is the result of few hours in Fusion360. I might have gone a little too ambitious with the front profile - I copied it from online pictures of Slingshot Infinity 76 wing but I think the final product will need to be simplified. Other than that I think that's a beauty! This is SG6041 airfoil profile, anything thinner would be too thin I think.
SG6041-1.PNG
SG6041-3.PNG
SG6041-2.PNG
SG6041-4.PNG

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Sat Oct 17, 2020 11:46 pm

salvatoreone wrote:
Sat Oct 17, 2020 9:52 am
Oh beautiful! Yeah, I think I'll go with the thicker option so SG6041. Is the front wing at 0° AoA relative to the fuselage? I know that stab is usually at negative 1-3° but I'm not sure about the front wing.

I was thinking about printing the mould but I'm a bit worried this will be more difficult to laminate than 3D printed foil. I think I'll go with the easiest way for my first foil but I already have some ideas I want to try out later such as making a mould for expanding foam which will later be laminated... I'm sure someone has already done it.
I think of 2 angles as important. The first angle is the angle of the front wing to the board (Or fuselage, since fuselage is usually square to mast and mast square to bottom of board). All you want here is for the board to not be pointing up or down comedically at cruising speed. For your front wing the angles of attack range from 11.5 degrees at 12.5km/hr, 0.7 degrees at 24 km/hr and -1.1 degrees at 35 km/hr. You are likely to be spending most time cruising in the top half of speed range (from the lowest drag dip and faster). So I would say setting front wing at 0 degrees to fuselage should be just fine.

The second angle is angle of stabiliser compared to front wing. Which you mention.

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Sat Oct 17, 2020 11:59 pm

salvatoreone wrote:
Sat Oct 17, 2020 11:02 pm
Okay... So this is the result of few hours in Fusion360. I might have gone a little too ambitious with the front profile - I copied it from online pictures of Slingshot Infinity 76 wing but I think the final product will need to be simplified. Other than that I think that's a beauty! This is SG6041 airfoil profile, anything thinner would be too thin I think.
SG6041-1.PNG
SG6041-3.PNG
SG6041-2.PNG
SG6041-4.PNG
NICE modeling. That looks great!

Some of my favourite wings simply use a large gradual curve in the middle and a little bit extra curve as it approaches the wingtips.
Capture.PNG
Capture.PNG (9.55 KiB) Viewed 290 times
The below paper gives a good overview of different wing plan shapes and also discusses wingtips in detail (see section 6.1) and it basically concludes that elliptical plan shape is a excellent choice. And when it comes to wingtips: wingtips are good at reducing wingspan a bit, but still less efficient than if you just added the wingtip height to your wingspan.

https://www.fzt.haw-hamburg.de/pers/Sch ... -09-10.pdf

fluidity
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Re: Wing profile info for backyard hydrofoil builders

Postby fluidity » Sun Oct 18, 2020 4:38 am

salvatoreone wrote:
Sat Oct 17, 2020 9:52 am
I was thinking about printing the mould but I'm a bit worried this will be more difficult to laminate than 3D printed foil. I think I'll go with the easiest way for my first foil but I already have some ideas I want to try out later such as making a mould for expanding foam which will later be laminated... I'm sure someone has already done it.
3D printing the core is definitely easier. If you want to have it match the NACA profile then you will need to subtract your layup thickness in advance. To get closed cells I use cubic infill on prusaslicer.

Composite layup thickness.
It's predominantly tension stresses on the underside and compression on top. Impact on the front. Much more stresses towards the centre of a foil.

So for the bottom, kevlar, Innegra, flax, basalt, glass all work well but something sandable for the outer layer.
On the top- kevlar/innegra inner layer if you want it impact resistant then unidirectional. Then clad the uni with something to stop the uni fibres splitting. If you just use a strip of uni then you will either need to falr the edges or pocket out the uni area by around a mm depending on your vacuumed uni thickness. 100mm uni is common, so that would be a 100mm wide strip+ allowance for the back cloth to detour behind.

I'm doing a CNC mould at the moment but it's for a fuselage.

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Sun Oct 18, 2020 6:27 am

I wouldn't do random patches. Just 5 layers of plain / twill 200g/m^2 carbon, simple and the job is done. Undersize core accordingly. Smooth surfaces are 100% the most important thing and patches are a pain for getting smooth afterwards.

salvatoreone
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Re: Wing profile info for backyard hydrofoil builders

Postby salvatoreone » Sun Oct 18, 2020 9:25 am

Yeah as far as I'm experienced with 3D printing, I have little experience with laminating so I think I'll go for the easiest solution for my first foil and just cover it evenly. As I get better at it I might try experimenting. How thick do you think 5 layers are going to be? I could make the profile 2.5mm smaller per side, is this enough?

I still need to figure out connecting it to my existing foil fuselage :lol: it can't be glued because I'll be using it for two wings. There is a video on YT showing one way of doing it

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Sun Oct 18, 2020 9:43 am

For 200g/m^2 carbon fibre thickennes are usually given at around 0.2-0.28 mm / ply. So 1-1.5mm for 5 layers, but check details for the specific cloth you are buying.

Might turn out a bit thicker if hand laminating (i would probably suggest fibreglass instead of carbon fibre if hand laminating in anycase, since it wont sit nicely around tight curves). Vacuum bag is well worth it for $50.

salvatoreone
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Re: Wing profile info for backyard hydrofoil builders

Postby salvatoreone » Sun Oct 18, 2020 12:11 pm

If it was only $50 I would be all in, but I don't have any pump to actually make the vacuum so unless there is some workaround I'll need to stick to handcrafting...

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Oct 19, 2020 12:28 am

salvatoreone wrote:
Sun Oct 18, 2020 12:11 pm
If it was only $50 I would be all in, but I don't have any pump to actually make the vacuum so unless there is some workaround I'll need to stick to handcrafting...
Hand layup should be fine. But would be easier to get 200 g.m^2 fibreglass to conform than carbon fibre. For Fibreglass I would probably go for 8 or so layers of 200 g/m^2 S-glass. And yes it might be best to do a handlayup wing first before adding complexity of vacuum bagging. I'm just a big fan of the consistent good results vacuum bagging gives.

Plenty of vacuum options around:
- Bag - Since you are in QLD, Aus, can pick one of these jumbo clothes vacuum bags at Bunnings for $7.40. It's reusable and I use it for boards as well.
https://www.bunnings.com.au/flexi-stora ... g_p4470473
- Vacuum pump: Plenty of options
Starting with a pump from a old fridge found on the verge
Check gumtree for secondhands, theres on in Perth for $50
Can use a cheap handpump
$120 brand new on the ebay
3CFM 1/3 HP Refrigerant Vacuum Pump Refrigeration 85 L/min R410A R32 VAC PUMP https://ebay.us/HVegd7
- Release film and tissue paper. Trojan fibreglass in NSW has good pricing or local fibreglass shop etc.

Happy building. Would be good to see a dedicated build thread for your wing. Cheers
These users thanked the author PrfctChaos for the post (total 2):
salvatoreone (Mon Oct 19, 2020 1:09 am) • fluidity (Tue Oct 20, 2020 10:19 am)
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