Wing profile info for backyard hydrofoil builders

[PrfctChaos]

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.

Those Aluminium moulds and the finish on the wings look awesome! Great result. I've been thinking about switching over to a rigid plastic myself (like a PVC), but its silly expensive compared to wood. Will have to keep on looking.
I'm sure your wings go really well. Another profile could've maybe just helped to push the top speeds a bit. I have spend a bit of time on the similar Neil pryde surf wings myself, they do turn really well.

Here are some updated results for 90Kg, and only considering profiles with at least 7% thickness. Just for interest and to show how it effects results.

1100 wing:
MH23 comes up top for balanced criteria and MH30 for low end biased criteria. H105 does similar to to the MH30, but just a bit more drag.

1600 wing:
MH30 comes up top for balanced criteria and NACA2407 for low end biased criteria. H105 does similar to to the NACA2407, but just a bit more drag.

I haven't made myself any race wings yet, just the pretty fast one shown on page 1 of the thread. It goes really well, but its still about 20%-30% larger than most race wings. The race wing I take out often on flat water is a KFA Mako2. And sometimes a Tarroa sword 2. Both were cheap as chips, since they are previous generation race gear (so not much use to the racers anymore), but the quality of the carbon masts and everything is top notch. I usually have a DIY freeride wing fitted to the Tarroa mast and stab, thats the setup I use most often on flat water. Still want to try my hand at a top speed wing, but will then need to start looking at a few more detailed design methods to push that envelope.

Will add some calcs for your +7% thickness freeride wind in a bit.

[PrfctChaos]

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).

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[PrfctChaos]

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.

Roof terrace? No way, this is for backyarders try on Seabreeze instead. Lol

On this one increasing the wingspan would really help. So might be worth having a think about the max wingspan you would be comfortable with. Considering handling, strength etc... I ran it for 1.3m in the below calcs, happy to look at more options.

Sweetspot comes up around 3000 cm^2. Ran for wingspan of 1.3m. Recommended profile being sd2030.

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Happy to a have a look at some more options once you've had a look.

[Freddyforlaunch]

I will try Seabreeze
Thanks for the recommendation @PrfctChaos!! Sounds like a suitable size and I like that the SD2030 is not that thin.

[robke]

Thanks a lot for help.
It does seem that the difference is very small between the airfoils on paper ( few hundred grams to a kilo). I wonder what would be total drag of a complete hydrofoil at maybe 30-40 kmh?
Maybe the selection of 'airfoil' is much less critical than wing shape, wing tips, shape of fuse and smooth transitions between the components?
Would be interesting to try two identical shaped wings with different airfoils, like 5% vs 12% thick, and see the difference... maybe some day

Btw, my big wing is just scaled small wing, same shape, angle...

I think I'll go for 750-850cm^2 and a 750mm span wing with s2055 profile. Try it flat, and then add some anhedral to feel the difference.
I'll keep you posted

[PrfctChaos]

Thanks a lot for help.
It does seem that the difference is very small between the airfoils on paper ( few hundred grams to a kilo). I wonder what would be total drag of a complete hydrofoil at maybe 30-40 kmh?
Maybe the selection of 'airfoil' is much less critical than wing shape, wing tips, shape of fuse and smooth transitions between the components?
Would be interesting to try two identical shaped wings with different airfoils, like 5% vs 12% thick, and see the difference... maybe some day

Btw, my big wing is just scaled small wing, same shape, angle...

I think I'll go for 750-850cm^2 and a 750mm span wing with s2055 profile. Try it flat, and then add some anhedral to feel the difference.
I'll keep you posted

I'm sure minimising drag at the fuse and stab is very important. I think hiding the fuselage behind the front wing is a good system, the older systems where the fuse was sitting on-top of the front wing probably not that good. In aeroplane design they know the wing to fuselage transition is important aerodynamically and go through some effort to calculate it accurately. With our small fuselages we can cheat by hiding the fuselage completely behind the front wing, yes it will still mess with it a bit, but who cares enough to optimise that interaction any further (probably not even race foil designers). And also it is easy to experiment with different stabs and feel the drag difference (More pronounced when higher speed of course). The Neil pryde small stabilisers are fat, thick things, I put one on the other day and had to stop a few times just to check if there was seagrass stuck to the foil it felt so draggy in comparison.

The only physical test results I have seen for complete foil setups come from the sailing world, for example, below is a example of results for Moth foils of different types (The total drag is measured, the source of the drag is split up theoretically). The size of the T-foil and tested speeds and weight is not distant from our own kiting use. Worth a read, I'll see if I can attach a PDF at the bottom. It can be seen that the major sources of drag are "Foil section and junction drag" as well as "induced drag", these are the same areas this thread concentrates on.

Full scale Moth CSYSPaperFeb09.pdf

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400g drag saving on 3 Kg is still a 13% improvement. And it is a free / no-strings-attached improvement when it comes to simply changing airfoil selection. Most other improvements in design often comes as a compromise to other values, so I will take a free improvement any day of the week. But I agree that wing size, shape and wingspan are definitely important (But wingspan comes with its own compromises off-coarse).

Also, if we take the 1100 wing for example. I was trying to pick the speed range which worked out the most suitable for the H105 profile, to show a direct comparison. Now if we change things up a bit and assume one wants to design that same size wing to do its best cruising at 35 km/hr (~22 knots) (not uncommon for faster surfwings). So I choose a speed range of 20-50km/hr, to have 35 km/hr near the middle, then results compared to the H105 start to diverge quite rapidly. Comparing the H105 to the MH23:
20km/hr - Drag is 1% higher for the MH23
28km/hr - Drag is 6% reduced for the MH23
35km/hr - Drag is 19% reduced for the MH23
43km/hr - Drag is 34% reduced for the MH23
50km/hr - Drag is 39% reduced for the MH23

[flaviocu]

Hi PrfctChaos
I'm following the discussion with great interest and great what and how the foils have been built, I've got a lot of inspirations already. I'm new to (kite-)foiling, and did buy a full foil set already (Gong ALLVATOR KITE 65cm, 712cm2) - haven't used it yet. As I'm an avid DIYer (built a TT and the Foilboard to go with the foil already), I'd love to build another kitefoil to go with my mast, fuselage and stab).
My plan is to 3d-print and vacuum-laminate, either using glass or carbon.

I'm on the heavy side (100kg naked) and I'd like to use the wing for kite-foiling in light-wind (and mostly in fresh/lake water), what profile and surface-area could you recommend? I can print to a width or height of ~40cm, so a span around max 80cm would be easiest to build for me.

Thank you very much for your help and kind regards
Flavio

[PrfctChaos]

Hi PrfctChaos
I'm following the discussion with great interest and great what and how the foils have been built, I've got a lot of inspirations already. I'm new to (kite-)foiling, and did buy a full foil set already (Gong ALLVATOR KITE 65cm, 712cm2) - haven't used it yet. As I'm an avid DIYer (built a TT and the Foilboard to go with the foil already), I'd love to build another kitefoil to go with my mast, fuselage and stab).
My plan is to 3d-print and vacuum-laminate, either using glass or carbon.

I'm on the heavy side (100kg naked) and I'd like to use the wing for kite-foiling in light-wind (and mostly in fresh/lake water), what profile and surface-area could you recommend? I can print to a width or height of ~40cm, so a span around max 80cm would be easiest to build for me.

Thank you very much for your help and kind regards
Flavio

Hi Flaviocu,

In all honesty I do not recommend learning on a DIY wing. It is difficult enough to learn without the handicap of second-guessing ones gear. I would really recommend that you either learn with the 712cm^2 gong wing you have at the moment (a bit small for your weight so will make it a bit difficult) OR just buy one of the Slightly larger Gong wings (Such as the Curve L, or even a Veloce L) (I use the Veloce L myself for the usual prone wing and use it often as a lightwind kite wing and it is great, I don't think it will be difficult to learn on and you will not outgrow it.)

BUT, if you are keen to DIY a lightwind wing, for your weight, the below should be good:

[flaviocu]

Thank you. If I can't ride (water and weather too cold and no wind anyway), I'm at least building to ride

[fluidity]

Thank you. If I can't ride (water and weather too cold and no wind anyway), I'm at least building to ride

That's how I operate too. Inconsiderate weather is the best time to design and build projects to try out for more optimal weather periods.

I'm only slightly heavier than you.
For wing surfing my first wing of 1800 sq cm was on the small side. Building a 2650 sqcm wing is letting me learn on days when the wind is around 15 knots where as before I needed 20 knots +