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Wing profile info for backyard hydrofoil builders

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PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Sun Nov 29, 2020 12:12 am

fluidity wrote:
Sat Nov 28, 2020 11:36 pm
PrfctChaos wrote:
Sat Nov 28, 2020 10:45 am
fluidity wrote:
Sat Nov 28, 2020 10:27 am
PrfctChaos,
I'm of the belief that many of the production wings are designed around capabilities and costing of CNC machine time
Yea, I'm not too sure how important the cost of machining a mould is to them. If a $10000 mould makes 1000 wings, then it's only $10 a wing, while a $5000 mould is $5 a wing. I think the materials + labour for each individual wing would take up a much more significant piece of the pie. But who knows.

I think you will figure out better ways to setup the cnc tool paths after a few goes, such as removing more of the stock, to make it easy to clear chips and space for the chuck. A bit of a thouvht change needed compared to 3d printing. You might be trying to push minimum machining time at the moment instead of other factors. I have a good laught now when opening up any of my old toolpath files, the aproach changed a lot over the first few projects.
I'm using ESTLCAM which is only $50 USD, Arduino for the controller and my custom mechanics. Estlcam will only run two machining paths in 3D per side per operation but I can load masks too, so potentially run a waterline operation over the fast changing height areas with finer tolerances but the same bit. in 10-20 years I'm suspect there will be a revolution in open source CAM program capabilities like happened with slicers for 3D printing.
I use Fusion360. It is free for Hobby use. I haven't found it lacking yet.

robke
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Re: Wing profile info for backyard hydrofoil builders

Postby robke » Mon Nov 30, 2020 12:46 am

Cheers from Norway everybody ! Nice forum with heaps of information.
I have been making my own foils and boards for some two years now, and they work nicely as they are (as much as I know, the only foils I've ever ridden).
I have a diy cnc router/mill, so I made molds from aluminum to skip the hassle of sanding and finishing the surfaces. I'll post some pics later.
Anyway, I used a H105 airfoil, which is quite thick, and may not the best choice for wing size/speed.
I would be grateful if PrfctChaos could run a sim for my two existing wings, as well with H105 for comparison if possible.

Small wing : span 700mm, center chord 201mm, area 1100 cm^2
Big wing : Span 850 mm , center chord 244mm, area 1600 cm^2
Hard to tell the speed window, I guess 10-40 kmh between both of them.

Wings have some anhedral, so the effective span is a bit less. Don't think it makes that much difference.
I plan on making a faster wing next, but I'm really curious how my current wings perform on paper.

Thanks in advance

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Nov 30, 2020 8:57 am

robke wrote:
Mon Nov 30, 2020 12:46 am

I have a diy cnc router/mill, so I made molds from aluminum to skip the hassle of sanding and finishing the surfaces. I'll post some pics later.
Anyway, I used a H105 airfoil, which is quite thick, and may not the best choice for wing size/speed.
I would be grateful if PrfctChaos could run a sim for my two existing wings, as well with H105 for comparison if possible.

Small wing : span 700mm, center chord 201mm, area 1100 cm^2
Big wing : Span 850 mm , center chord 244mm, area 1600 cm^2
Hard to tell the speed window, I guess 10-40 kmh between both of them.
Aluminium moulds! Please do put up some pics. That sounds like some NICE moulds!

NB: No Info on your weight, so I'm running the calcs for 80Kg, please let me know if this is not close?

Have added the H105. Please see results below.

Small wing : span 700mm, centre chord 201mm, area 1100 cm^2:
I ran this one for a speed range of around 10-25 knots (16.5-40 km/h), it was the speed range that looked appropriate to me in the calcs. (Lower speed than that and the induced drag just becomes massive)
Calcs show that the H105 does well at the low end of the speed range. However, for a low speed biased design the mh30 beats it by a slim margin. And NACA1506 comes out tops for the general (Balanced) selection.
Capture.PNG
Big wing : Span 850 mm , centre chord 244mm, area 1600 cm^2
I ran this one for a speed range of around 15-30 km/h, it was the speed range that looked appropriate to me in the calcs. (Lower speed than that and the induced drag just becomes massive)
For a low speed biased wing the NACA2405 would perform better than the H105 according to the calcs. And NACA1605 comes out tops for the general (Balanced) selection.
Capture2.PNG
Happy to run the calcs for a fast wing. Let me know what you have in mind. Whether you want to go VERY fast and small or just freeride fast. I have pretty high hopes for my new and improved freeride wing being made at the moment (750 mm wingspan, 900 cm^2 area posted a page or two back.)
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Freddyforlaunch
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Re: Wing profile info for backyard hydrofoil builders

Postby Freddyforlaunch » Mon Nov 30, 2020 4:54 pm

Hi @prfctchaos,

Do you also give advice to people not having a backyard, but a roof terrace? :)
I am going to build an electronically driven hydrofoil. So this has some extra weight for battery and such. Also I would like it to take off at low speeds, since I would
like to foil in places where there are speed limits. The mass of the board plus me is 110kg, and I would like to take off at 9kph, cruise at 12kph and with max speed 20kph. Typical fresh water temperature is 15 degree celsius.
Could you advice on an airfoil, span and wing area? If I would have to guess the span and area, I would say 1.2m and 4000cm^2. I would like to have minimal drag, to maximize the range before the battery is empty.
Last edited by Freddyforlaunch on Mon Nov 30, 2020 10:10 pm, edited 2 times in total.

Freddyforlaunch
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Re: Wing profile info for backyard hydrofoil builders

Postby Freddyforlaunch » Mon Nov 30, 2020 4:58 pm

And I read that the H105 profile that @robke mentions is designed to prevent cavitation. Does your "selector" also takes into account cavitation?

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Schietwedder
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Re: Wing profile info for backyard hydrofoil builders

Postby Schietwedder » Mon Nov 30, 2020 5:52 pm

I doubt you will be fast enough encountering cavitation no matter what profile you are using (45-50kts) so it doesn´t matter IMO.
Or do you mean separation or ventilation (often confused with cavitation).

Cavitation means the pressure on the suction (upper) side of the foil is so low that the water evaporates to gas bubbles which will increase drag drastically and can cause damage on the foil surface after time. It usually can be found on fast turning ship propulsion units or foils operating 50kts+
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robke
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Re: Wing profile info for backyard hydrofoil builders

Postby robke » Mon Nov 30, 2020 7:21 pm

Excellent PrfctChaos ! So not too bad actually with H105 profile.

My weight is probably around 90kg with the gear on, but I'm pretty sure the pressure on the foil varies between 0-130kg when kiting .

I would definitely like to try a thinner profile for my next wing. The h105 is around 12% max thickness vs NACA with 5% ( much less aluminum for a mold :) )
Probably that's why it looks a bit better at low end.

My idea for the fast wing is pretty similar to what you plan on making 800-900 in area, and span of 750 seems reasonable. I would prefer something a bit thicker than 5% for hollow/pu filled composite wings, maybe in 7-8% range for sake of stiffness and rigidity.
At 5% thickness and 150mm center chord it's only 7.5 mm thick which sounds like it should be made of solid carbon/glass. Thou i could mill the wing from 10 mm aluminum and just go test ride it. That would take a day or two and almost no manual labor. That actually sounds like good game plan. Will think about it for a bit before I begin.

What is the race wing you have PrfctChaos ? would like to try one these as well :) The whole idea with making my own was to learn and try different wings, stabs, mast lengths etc. There wasn't that much info on web when I made my first foil, around 3 years ago (which got me 11 stitches on my palm). It was a very exciting process making the equipment and learning to kitefoil.
Last edited by robke on Mon Nov 30, 2020 8:59 pm, edited 1 time in total.

robke
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Re: Wing profile info for backyard hydrofoil builders

Postby robke » Mon Nov 30, 2020 8:17 pm

Don't mean to spam, but with pics more is better.
Attachments
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Freddyforlaunch
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Re: Wing profile info for backyard hydrofoil builders

Postby Freddyforlaunch » Mon Nov 30, 2020 10:03 pm

Schietwedder wrote:
Mon Nov 30, 2020 5:52 pm
I doubt you will be fast enough encountering cavitation no matter what profile you are using (45-50kts) so it doesn´t matter IMO.
Or do you mean separation or ventilation (often confused with cavitation).

Cavitation means the pressure on the suction (upper) side of the foil is so low that the water evaporates to gas bubbles which will increase drag drastically and can cause damage on the foil surface after time. It usually can be found on fast turning ship propulsion units or foils operating 50kts+
Thanks @Schietwedder. Indeed I was confused with separation and ventilation. Quoting Tom Speer: "The H105 hydrofoil section was designed to avoid laminar separation and ventilation when operating at low speeds and moderate angles of attack, while still having low velocities at small angles of attack to avoid caviatation at high speeds"

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Nov 30, 2020 10:34 pm

Hi Freddy, one thing to remember about the boat foils, is they have it in a L shape piercing the surface. Which makds it much easier for the profile to suck air down the low pressure face.

With our T shape hydrofoils, we have the advantage of the mast profile not producing very low pressures, so that helps to make it more difficult for air to get sucked down to the wing surface. I don't worry about it at our freeride speeds either (because it hasn't been a problem for me yet), but there are definately ways to calculate it. I would not include it in my Lift/Drag optimisation program, but individual users are more than welcome to check it for the profiles that get selected.


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