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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 » Thu May 27, 2021 2:18 am

PrfctChaos wrote:
Thu Jan 14, 2021 4:42 am
salvatoreone wrote:
Thu Jan 14, 2021 1:53 am
PrfctChaos wrote:
Tue Dec 01, 2020 4:10 am
Hi Robke,

I think the below freeride wing looks pretty good. 750 mm wingspan, 750 cm^2 area (It is just a touch larger than the theoretical minimum zone, but going down to 600-675 cm^2 only has a very small advantage). Recommended profile is the S2055. Make it in Polished aluminium would look awesome (would be a bit worried about damaging the thin trailing edge, but would definitely look awesome).

Capture.PNG

Capture2.PNG
Hi PrfctChaos,
I'm really itching to make another wing and I've been searching through existing calculations for some inspiration as to what I actually want and that one above looks promising. All the parameters are essentially valid for my case but I was wondering what would change if we make the wingspan smaller (you mentioned 600-675 cm2 has some advantage)? I think smaller aspect ratio wing could be a bit easier to make, store and transport, also I'm not sure if I'm after a hardcore racing wing yet :lol:

Also in another reply, you mentioned calculations for a stab. Are you able to calculate the optimal stab parameters for the above wing?
Nice, a fast freeride wing is awesome fun, good choice.

So for 750 mm wingspan and 750 cm^2 area, the results look like this. s2055 profile wins best general profile (Drag of around 2.5 Kg near middle of the range). And rg14a147 doing a bit better in the top half of the speed range (Best High speed biased selection).

Capture2.PNG

For a smaller wingspan of 700 mm, the optimum shows up at a area of 700 cm^2 for this speed range. s2055 profile wins best general profile (Drag of around 2.6 Kg near middle of the range).

Capture3.PNG

I'm sure both of these will have plenty good mid and top speeds. Can't go wrong with either.

Stab optimisation and matching for a specific front wing......... Hmmm..... It is possible, but the main problem is that there are too many extra measurements and info needed. For example, you would need to calculated / estimate the total drag being created by the front wing, mast, fuse and stab itself with the fuse length and front wing centre of lift over the speed range. Just to calculate how much unbalanced moment is left that the rider needs to take of. To optimise, one would then need to minimise the drag and unbalance moment for all the different possible stab profiles as well as a range of adjustment angles for the stab as well as front wings. I'm putting it in the too hard basket for now.

However, I can tell you that my current favourite stab is a fast little stab, that has a wingspan of 390 mm, Max chord of 50 mm and uses a NACA0008 profile. I find it to be really low drag and fun compared to many commercial stabs. Well balanced at a downward angle of 2.5 degrees on my fast surf wing. For your smaller wing you might want to start at about 2 degrees if I had to guess.

Capture5.PNG
So I have finally found some time to finish the front wing + stab. They were made in the 3D printed mould and unfortunately I learned a painful lesson not to use a big piece of sponge to fill the mould between the halves... When I closed the mould and squeezed the sponge between the layers of carbon, the sponge released a huge amount of air bubbles which all travelled to the surface of my wing (which I was obviously unaware of)... This resulted in a terrible surface finish and it took me few more days to fix it. I learned my lesson and for the stab I used a thickened epoxy as a filler and it worked fine, also I put a lot more attention to finishing the mould so the surface finish from the pictures is out of the mould with zero sanding. By the way the stab took less than 48 hours from design to finish :D

It's all looking a bit rough, I'll finish it nicely if it proves to be working fine :lol:

Two questions to you guys:
- How do you finish your moulds to get a nice surface finish?
- My wings are always a little bit "elastic", are you achieving 100% rigidity when you make wings?
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PrfctChaos (Tue Jun 22, 2021 12:43 am)
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PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Jun 21, 2021 1:48 am

salvatoreone wrote:
Thu May 27, 2021 2:18 am
Looks good Salvatoreone, nice result.

Good tip about avoiding using a sponge (or something else that will release air) in the mould.

My moulds I just machined out of hardwood. Smoothed them with a bit of light handsanding. Then a good number of wax coats to give a easy release (and the wax probably does a good job of filling up any little surface imperfections).

Have ended up with some very flexy wings (Foam core and just a few layers of fibroglass) and very rigid ones (hardwood core with 5 layers of CF, or just full CF wings). I think I liked the stiff ones better.

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Jun 21, 2021 2:14 am

Thanks to comments from Thibkite and Direnc, pointing out that the default Xfoil Ncr of 9 I was using was too high. Glad to have some cross-checking to point out any details I missed. Have now re-run all polars for Ncr of 2. So results being shown from now on is likely to look a bit different to previous results, with new sections likely to make it to the top of the charts, which is excellent, we might be getting somewhere exciting.

Roadmap for release of software:
I'm keen to release a free downloadable version of the software. So that everyone can have a play with it at home and see how selections and results change as they play with the inputs. This will be a free of charge community project and is due to be released in a few weeks. SuperTed and myself have been burning the midnight oil to make it a reality. (There will likely be a donate button somewhere, if someone feels that they got value from the software and would like to buy the team a beer, that would be sweet. We will happily look at your hydrofoil pics at the pub over a cold one and cheers some ripping DIY foils).

10minmayl
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Re: Wing profile info for backyard hydrofoil builders

Postby 10minmayl » Sun Jun 27, 2021 9:23 pm

Exciting. Would love to have a look.

ps does anyone here have any insight on what airfoil profile Kitesurf kites are designed on? Are they? Is it guesswork

PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Mon Jun 28, 2021 12:01 am

10minmayl wrote:
Sun Jun 27, 2021 9:23 pm
Exciting. Would love to have a look.

ps does anyone here have any insight on what airfoil profile Kitesurf kites are designed on? Are they? Is it guesswork
Between LEI kites and foilkites, I think I remember some airfoil chat going on in one or two of the below threads.

viewtopic.php?f=197&t=2391006&p=1133940 ... e#p1133940
viewtopic.php?f=197&t=2402861&p=1093026 ... e#p1093026
viewtopic.php?f=197&t=2402224&p=1045653 ... e#p1045653
viewtopic.php?f=1&t=2392855&p=1031125&h ... e#p1031125
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10minmayl (Mon Jun 28, 2021 12:39 pm)
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PrfctChaos
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Re: Wing profile info for backyard hydrofoil builders

Postby PrfctChaos » Thu Jul 22, 2021 5:28 am

We finally got to a Version 1 of the foil design / optimisation program that is fairly clean and easy to use. Give it a download and try at the below link.

Wing_Bot V1.0


Happy playing / designing.

We've got more ideas for small optimisation wins, so more to come. Also trying out if a subreddit (r/Wing_Bot) makes any sense. Come on over and chat about foil design. Hopefully it can become a good foil design focussed community there.

Cheers,


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