Wing profile info for backyard hydrofoil builders

[sekal77]

What is the reason Wing_Bot is not showing low speed data for the profile? Is it stall below this speed or the data is not existing?
I'm trying to design a front wing similar to Axis 1310 PNG. What would be the best profile for low speed pumping?

[robke]

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,

Wanted to ask this for some time now. Is there really such a big difference in drag vs water temp ? When I simulate mh38 profile at 25kmh (900 span, 1000cm2, 80kg) at 5 deg C I get around 2.6 kg drag and around 2.2kg at 30 C. Seems like the difference is quite big. Curve shape is different as well at 5 C and 20 C. Seems a bit odd.

[Schietwedder]

Referring to the paper of Albion Bowers Prandtl-D wing or an update of the 1933 Prandtl paper which was discussed earlier here:

Short summary of the paper: Ludwig Prandtl submitted two ideal solutions to minimise induced drag on a wing:

1910 Elliptical lift distribution (least drag for a given wingspan) found coombination with adverse yaw aka "dutch roll"
1933 Bell shaped lift distribution (least drag for a minimum structural mass of wing, or bending moment, leaving the wingspan open) found in combination with proverse yaw.

Defintion of pro and adverse yaw:
Adverse yaw: Wing rolls in one direction -> wants to yaw in the other direction. Results in a wobbly motion also known as dutch roll
Proverse yaw: Wing rolls in one direction and yaws in the same direction ---->super nice turns!

Now for kite/surf/wingfoils elliptical spanload wings have two drawbacks:
-1: Elliptical lift distribution sheds most of the vortices in the wingtips, because the lift is reduced there rapidly as well. (Helmholtz vorticity theorem: Change in circulation (lift) is proportional to change in vorticity) Now with lot of vorticity and lift close to the wingtip it is clear that the wing will also be prone to ventilation in sharp banked turns or canted upwind riding as in kitefoiling sucking down air fronm the surface)

-2: Adverse Yaw: The wings just don´t turn as nice as they could do and (although the mast is acting as a vertical stabiliser) roll and yaw are always (to a degree) coupled in adverse directions.

So although the Prandtl theory is probably not so widely known among foil designers, the more I research it the more it becomes clear that this theory is the reason why we see more and more high AR foils that actually turn really nice for surf foiling being twisted (or using lower cl airfoils, or a combination of both) at the wingtips. (With massive twist (outwash) bowers also achieved the bell shaped lift distriuton)
Nice side effect: glide and induced drag do not suffer going to a bell shaped loaded wing but span might be a bit bigger. Wing also does not ventilate.

Now if you simulate the whole surf foil (frontwing, immersed part of mast, and stailiser) with a lifting line theory based CFD-Potential flow solver like XFLR 5 and perform a L/D analysis and a staility analysis you get a really good understanding how it works, what twist is enough or too much, how it affects glide and turning.

Planning to do some front wings too (not before next winter) for my sabfoil fuselage. Think it is a good start building a parametric foil designer into XFLR5 and 3D scan the wings (and tailwings) I have (799, 633, 645, 425,483), put them into XFLR 5 and see the data as a validation for future wings to have a refference that the simulation works.
Guess it´s the next step from 2D Profile choice (Which also works in XFLR 5 (based on XFOIL) even inverse methods to 3d lifting line theory analysis which is also numerically very efficent (based on potential flow theory) and easier/cheaper to perform valid results compared to RANSE for the advanced hobbyist.

[x3oo]

Referring to the paper of Albion Bowers Prandtl-D wing or an update of the 1933 Prandtl paper which was discussed earlier here:

Short summary of the paper: Ludwig Prandtl submitted two ideal solutions to minimise induced drag on a wing:

1910 Elliptical lift distribution (least drag for a given wingspan) found coombination with adverse yaw aka "dutch roll"
1933 Bell shaped lift distribution (least drag for a minimum structural mass of wing, or bending moment, leaving the wingspan open) found in combination with proverse yaw.

Defintion of pro and adverse yaw:
Adverse yaw: Wing rolls in one direction -> wants to yaw in the other direction. Results in a wobbly motion also known as dutch roll
Proverse yaw: Wing rolls in one direction and yaws in the same direction ---->super nice turns!

Now for kite/surf/wingfoils elliptical spanload wings have two drawbacks:
-1: Elliptical lift distribution sheds most of the vortices in the wingtips, because the lift is reduced there rapidly as well. (Helmholtz vorticity theorem: Change in circulation (lift) is proportional to change in vorticity) Now with lot of vorticity and lift close to the wingtip it is clear that the wing will also be prone to ventilation in sharp banked turns or canted upwind riding as in kitefoiling sucking down air fronm the surface)

-2: Adverse Yaw: The wings just don´t turn as nice as they could do and (although the mast is acting as a vertical stabiliser) roll and yaw are always (to a degree) coupled in adverse directions.

So although the Prandtl theory is probably not so widely known among foil designers, the more I research it the more it becomes clear that this theory is the reason why we see more and more high AR foils that actually turn really nice for surf foiling being twisted (or using lower cl airfoils, or a combination of both) at the wingtips. (With massive twist (outwash) bowers also achieved the bell shaped lift distriuton)
Nice side effect: glide and induced drag do not suffer going to a bell shaped loaded wing but span might be a bit bigger. Wing also does not ventilate.

Now if you simulate the whole surf foil (frontwing, immersed part of mast, and stailiser) with a lifting line theory based CFD-Potential flow solver like XFLR 5 and perform a L/D analysis and a staility analysis you get a really good understanding how it works, what twist is enough or too much, how it affects glide and turning.

Planning to do some front wings too (not before next winter) for my sabfoil fuselage. Think it is a good start building a parametric foil designer into XFLR5 and 3D scan the wings (and tailwings) I have (799, 633, 645, 425,483), put them into XFLR 5 and see the data as a validation for future wings to have a refference that the simulation works.
Guess it´s the next step from 2D Profile choice (Which also works in XFLR 5 (based on XFOIL) even inverse methods to 3d lifting line theory analysis which is also numerically very efficent (based on potential flow theory) and easier/cheaper to perform valid results compared to RANSE for the advanced hobbyist.

I stumbled upon the same talks but there is a misassumption. Adverse yaw emerges through ailerons. Your hydrofoil doesnt have ailerons. leaning sideways doesnt produce adverse yaw, except for maybe anhidral wings.

[Kaimana]

I get the feeling that .....

Hey PrfctChaos, hoping you're still checking this board occasionally. My family boatshop just embarked on developing a foil-borne 30-footer and are looking for foil-design or analysis software. You'rs popped up, and I'd like to use it commercially, so please hit me at skipper at oceanpeople dot org with an email.

We're just beginning foil development for a small 18-foot foiling multihull we plan to use as a test bed to develop that 30-footer from. We can make foils cheaply and quickly with our mold technology, so rather than buy an expensive software, will probably just do tests with some $300 iterations of actual foils.

That's the kind of shop we have; we just build it. You've got to build it anyway to test it, and how many projects are there where companies spent $150k (or $15 mil) on engineering to find out they can't get the prototype to work?

So we brainstorm, do some caveman calculations, then build the first one from cardboard and duct tape; build the second one from exterior plywood and glue; and build the third one from fiberglass and epoxy.

In 1974, when I was 22, I designed and built a 4-foot diameter, 3-bladed electric wind turbine for my 37-foot sailboat, because there was nothing on the market smaller than 12 feet diameter, and because the Stone-Age PV panels they had back then were not only expensive, but used regular window glass as a substrate and cover. Real dangerous on a sailboat.

I got a new 45-amp tractor alternator, the smallest I could find; and rewound it with smaller wire to put out at half the rpm. I geared that up 2:1 with a Dayco Cog Belt drive, which has the same power transmission efficiency as an oil-bath gear drive, and is a lot cheaper! Resulting shaft speeds for power output were in the vicinity of what I could get from a windmill blade.

I figured out the right NACA foil section to use for my desired wind speed range, transferred it to graph paper, made a jig to cut the twist from root to tip into the 2-foot long polyurethane foam blade blank, and did the cutting with a hot, taut nichrome wire on a jig. I glassed the resulting shape with epoxy and E-glass, then glued a tubular aluminum center shaft into it.

It worked great! It put out its own field current in 8 knots of wind, put out 8 amps at 12 knots of wind, maxed out at 30 amps in 20 knots of wind. It made more power than I could use on the boat, and meant I didn't have to run the engine to charge the batteries. I think I had $125 into it when done.

I was checking out state-of-the-art in small windmills back in 2018 and found one with three of the features I'd put on my mill back in 1974, and they had patented them! I got a good laugh out of that!

Anyway, if you're here and you've got time I'd appreciate a ping. Thanks! With Warm Aloha, Tim

[PrfctChaos]

I get the feeling that .....

Hey PrfctChaos, hoping you're still checking this board occasionally.

Hi mate, sorry for being slow. I was doing a little bit of traveling .

That sounds like a fun project. Please feel free to use the software for your sailboat development. I am planning on releasing a opensource version (that will basically have the capability of this V1.0 software in anycase). I just need to get some time infront of the computer to make it happen.

I'll shoot you e-mail in anycase, then you have my contact details if you need any special help. And it be great to see some of the builds and results you get.

[PrfctChaos]

V1.1 Update
This is just a small update. To give users information about the Angle of attack of the foil through the speed range. No other changes on this version, but a few larger updates are coming.
V1.1 can be downloaded here:
https://www.reddit.com/r/Wing_Bot/

The results column on the bottom right now gives the Drag value (in Kg, to 1 decimal) and Angle of Attack (in Degrees, to 1 decimal).

[fluidity]

Referring to the paper of Albion Bowers Prandtl-D wing or an update of the 1933 Prandtl paper which was discussed earlier here:

Short summary of the paper: Ludwig Prandtl submitted two ideal solutions to minimise induced drag on a wing:

1910 Elliptical lift distribution (least drag for a given wingspan) found coombination with adverse yaw aka "dutch roll"
1933 Bell shaped lift distribution (least drag for a minimum structural mass of wing, or bending moment, leaving the wingspan open) found in combination with proverse yaw.

Go-foil and Triton had a crack at the bell shaped lift distribution after I reposted Albion Bowers research on bird's wingtips, Ludwig Prandtl's second paper and the Horton brother's delta here.

Go-foil pretended their cut and re-welded tip twist was for other reasons and Triton are very quiet about their tip twist it but the effect is very real.

I made one HA tubercles wing with progressive tip twist and I liked it so much I made a smaller and bigger one as well. I would have done it earlier than Feb2022 but it was only for me and I developed the CAD algorithm myself, I'm not affiliated with any manufacturers. I printed in pieces for the models, molded around them and then filled the molds with carbon.

Performance differences:
Fantastic low speed glide with very late stall.
Higher stall angle.
High breach resistance.

I don't like other wings of the same area now, mine have better low speed lift and earlier takeoff. I still have some tweaks to experiment with but you couldn't pay me to swap to an AXIS foil of the same area, I made mine to fit Axis fuselage but Axis foils are for others to ride. Don't get me wrong, Axis HA are faster with better high speed glide than my Feb2022 creations, I just much prefer the handling of mine.

[vol]

V1.1 Update
This is just a small update. To give users information about the Angle of attack of the foil through the speed range. No other changes on this version, but a few larger updates are coming.
V1.1 can be downloaded here:
https://www.reddit.com/r/Wing_Bot/

The results column on the bottom right now gives the Drag value (in Kg, to 1 decimal) and Angle of Attack (in Degrees, to 1 decimal).

awesome! this is the greatest tool for foil design