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Wing profile info for backyard hydrofoil builders

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robke
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Re: Wing profile info for backyard hydrofoil builders

Postby robke » Fri Apr 02, 2021 11:59 am

Hei guys, the spring came and brought some motivation :)
Front wing rg14a147, span 750, area 750
Stab naca0008, span 460, area 280
Looks fast, and dangerous :/
Might have a chance to try it tomorrow
Attachments
IMG_20210402_124806.jpg

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Sun Apr 04, 2021 10:48 am

Damn! Like a sportscar, it looks fast even standing still in a photo.

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ZachMoves
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Re: Wing profile info for backyard hydrofoil builders

Postby ZachMoves » Sat Apr 10, 2021 5:13 am

Check out WingHopper.com! A great compliment to this tool. Perhaps we can combine them somehow?

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Re: Wing profile info for backyard hydrofoil builders

Postby kostantin » Sat Apr 10, 2021 11:11 am

robke wrote:
Fri Apr 02, 2021 11:59 am
Hei guys, the spring came and brought some motivation :)
Front wing rg14a147, span 750, area 750
Stab naca0008, span 460, area 280
Looks fast, and dangerous :/
Might have a chance to try it tomorrow
Greetings

Are the wings printed ?

tks

Kosta

robke
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Re: Wing profile info for backyard hydrofoil builders

Postby robke » Sat Apr 10, 2021 6:31 pm

kostantin wrote:
Sat Apr 10, 2021 11:11 am
robke wrote:
Fri Apr 02, 2021 11:59 am
Hei guys, the spring came and brought some motivation :)
Front wing rg14a147, span 750, area 750
Stab naca0008, span 460, area 280
Looks fast, and dangerous :/
Might have a chance to try it tomorrow
Greetings

Are the wings printed ?

tks

Kosta
They are machined from aluminium

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Apr 12, 2021 1:45 am

Hi All,

In other news, the profile selection tool has gotten another upgrade. 3rd upgrade for those keeping score.

1st major version, Aug 2020, included only NACA4 and NACA 5 profiles, around 1000 profiles.
2nd major version, Sep 2020, added basically all the airfoils one can find on Airfoils.com, so up to around 2500 airfoils. Lift induced drag was also added.

Now for the 3rd major version:
In previous versions, the calculation was fairly two dimensional. That means that the average chord length was calculated for the wing and then all lift / drag calculations were based on that single average chord length. So some specific behaviour of the profiles at the extremes of the wing might be missed / ignored (long chord in the middle of the wing and short chord at the wingtips).

The program has now moved to more detailed 2.5d approach. Where the wing is chopped into 10 sections (from middle to the tip), each of these sections are then analysed seperately, before being added together again to find the optimum for the wing as a whole. What it means is:
- The program can now use the correct Reynolds numbers for the bigger chords in the middle of the wing and for the smaller chords nearer the tips. Thus better accuracy. And profile selections where certain parts of the wing would have stalled can be avoided.
- It also means that calculations can accurately be performed for various wing plan shapes. (Typical choices are Elliptical, Tapered or Custom). Induced drag is still only estimated, the required Oswald factor for a given plan shape needs to be entered manually. However, parasitic drag is calculated accurately.
- Wingtip washout can now be calculated accurately (when it comes to parasitic drag). Since each of the 10 sections can be rotated to their respective Angle of attacks for washout.

This does not change the results significantly, but one will notice some small differences. Here is a example with Spirus' wing from the previous page. Comparing Version 2 and Version 3 results.

Version 2:
Capture - Spiru 700 mm x 800.PNG
Version 3:
Capture - Spiru 700 mm x 800Ver3.PNG

robke
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Re: Wing profile info for backyard hydrofoil builders

Postby robke » Sun Apr 18, 2021 9:41 am

Nice addition to the software. Now things will be even more accurate.
Do you think wing washout is worth considering on our foils?
Managed to try my alu setup lately. Surprisingly it performed well straight away. I had the stab set at -1 degree and it felt good like that.
The wing was stable in pitch and roll, stall speed was less than i expected, so that's nice. It was noticeably faster than my other wings, but i tried it with a 70cm mast, and the waves were up to 70 cm, a bit tricky to go fast.
One thing I notice with aluminium wings is the whine. They have a specific sound, a high pitched whine. My other wings are quite silent, maybe some low frequency whooshing.

Two practical questions.
What is your typical back foot position? Front of the mast, on the mast or back?
When you hit that chop and smal waves, do you feel the currents/lift from them? Sometimes if I ride a bit faster in the direction of waves, overtaking them, I might get so much lift that I almost breach. When I pass the wave it's like a sink hole, I need to pitch it up considerably for not to touchdown.

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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Apr 19, 2021 6:59 am

"Do you think wing washout is worth considering on our foils?" - Let me run a few cals on this one. From what I have seen on the calcs I think the sometimes mentioned 2 degree washout value is way too high. Ideally we want to try and maintain a Elliptical lift distribution. Maybe a small (probably mush smaller than 2 degrees) amount of washout helps to get a tapered wings lift distribution closer to elliptical? Or maybe it helps with some of the Reynolds number effects as the chord changes? Some detail things I might do a set of simulations for later. In the latest iteration of the program I can set up a comparison of how far the achieved lift distribution varies from the ideal lift distribution, so some washout or area tweaks might help a bit to optimise that later on. Leave it with me for a few weeks.

Good to hear the new wing held up, it really looks awesome in the Alu. :thumb:

My usual steps to get wings quite is.
1. Surface finish - Usually I try and get it to a very smooth 400-800 grit finish (keeping the lines in the direction of flow). Have had a few sessions on hastily finished wings in the past and a good surface finish made crazy differences. With the rough finish some feel like one is riding on gravel and another one was shaking like crazy. And they changed to completely smooth and quite with a sorted out surface finish.
2. Trailing edge - Have had good results with a 30 degree angle on the trailing edge (I put the angle on the top of the front wing, bottom of stab.). And then just take of the sharpness of the edge by squaring off the sharp edge a little bit. If I remember correctly, this Delta hydrofoils video is a good one.

I'm sure you will get it whisper quite. Remember the stab as well.

"What is your typical back foot position? Front of the mast, on the mast or back?" - I think I have my back foot on the front bolts of the mast on most foils, or maybe on the mast.

"When you hit that chop and smal waves, do you feel the currents/lift from them? Sometimes if I ride a bit faster in the direction of waves, overtaking them, I might get so much lift that I almost breach. When I pass the wave it's like a sink hole, I need to pitch it up considerably for not to touchdown." - I only use a 70 cm mast with the surf foil setup. And yes can be a handful on BIG chop. But usually use a 100 or 105 cm mast for freeride kiting, so can happily ignore the chop most of the time :D .

robke
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Re: Wing profile info for backyard hydrofoil builders

Postby robke » Tue Apr 20, 2021 7:14 pm

Thanks for the reply. I think they use wing washout on aircraft in part to reduce wing tip flutter. I think it might reduce induced drag a bit too.
I will give a shot on fixing trailing edge. It's finished mostly like my other wings, but those are quite quiet.

On my foils I have my foot close to the middle of the mast, a bit more back maybe. I guess each setup is different.

I was wondering for some time about the chop lift, nobody seems to mention it in the foil vids :)

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Re: Wing profile info for backyard hydrofoil builders

Postby salvatoreone » Thu Apr 22, 2021 11:49 pm

PrfctChaos wrote:
Mon Apr 12, 2021 1:45 am
Hi All,

In other news, the profile selection tool has gotten another upgrade. 3rd upgrade for those keeping score.

1st major version, Aug 2020, included only NACA4 and NACA 5 profiles, around 1000 profiles.
2nd major version, Sep 2020, added basically all the airfoils one can find on Airfoils.com, so up to around 2500 airfoils. Lift induced drag was also added.

Now for the 3rd major version:
In previous versions, the calculation was fairly two dimensional. That means that the average chord length was calculated for the wing and then all lift / drag calculations were based on that single average chord length. So some specific behaviour of the profiles at the extremes of the wing might be missed / ignored (long chord in the middle of the wing and short chord at the wingtips).

The program has now moved to more detailed 2.5d approach. Where the wing is chopped into 10 sections (from middle to the tip), each of these sections are then analysed seperately, before being added together again to find the optimum for the wing as a whole. What it means is:
- The program can now use the correct Reynolds numbers for the bigger chords in the middle of the wing and for the smaller chords nearer the tips. Thus better accuracy. And profile selections where certain parts of the wing would have stalled can be avoided.
- It also means that calculations can accurately be performed for various wing plan shapes. (Typical choices are Elliptical, Tapered or Custom). Induced drag is still only estimated, the required Oswald factor for a given plan shape needs to be entered manually. However, parasitic drag is calculated accurately.
- Wingtip washout can now be calculated accurately (when it comes to parasitic drag). Since each of the 10 sections can be rotated to their respective Angle of attacks for washout.

This does not change the results significantly, but one will notice some small differences. Here is a example with Spirus' wing from the previous page. Comparing Version 2 and Version 3 results.

Version 2:
Capture - Spiru 700 mm x 800.PNG

Version 3:
Capture - Spiru 700 mm x 800Ver3.PNG
Damn mate, good job! This tool is growing into something powerful! :D :D

I can actually see how the output from the spreadsheet could be used to generate a model in some CAD (like Solidworks or something) with a click of a button. If the model was fully parametric this could be relatively easily done and I probably even have the skills to do that. The only thing you would need to do with it is creating some interface between the wing and fuselage.
ZachMoves wrote: Check out WingHopper.com! A great compliment to this tool. Perhaps we can combine them somehow?
Sort of what this does, it's actually a great tool! It could save many hours of modeling... But I don't see an option to change the foil profile which is basically the whole point of this post :lol:


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