Wing profile info for backyard hydrofoil builders

[nemoz]

printing polycarbonate it's not easy at all... you need nozzle temperature higher than normal, you have to hack the firmware to reach it in the majority of the printers.

[PrfctChaos]

And you still need to find a way to connect the pieces together structurally. And then fill and smooth out the gaps etc, that there will inevitably be between the pieces...

Quite a challenge to do without laminating / moulding

[andremi]

I have studied how to upgrade my Ender 3 to print polycarbonate, and this does not seem like too difficult of a task. Plus lots of success stories of others printing polycarbonate with, so I have good confidence that I can make it work.

True, the structural integrity is an issue: the Javelin hydrofoil was printed as one unit on a commercial grade 3d printer, but we cannot do that size print on a consumer grade printers.

I thought I would split the foil into 3 parts — just like most have done — but would insert round holes on one side and cylinders on the other side, as a part of the model. (or maybe make holes everywhere and print cylinders separately, might be easier as no need for printing with supports, etc). So when you connect the parts, the cylinders would go into the holes and this would align parts perfectly. With epoxy this should hold everything together. But completely unsure if this design is not going to cause a weak point on cylinders (or make the wing weaker) thus needing lamination and defeating the whole purpose of polycarbonate use.

[salvatoreone]

Hi,
I am following this thread with a great interests. Lots of great info, thank you! I just got into foiling myself (on slingshot hover glide nf2) and thinking that at some point I might end up printing a different foil that would fit into slingshot fuselage.

Did anyone consider 3d printing a foil with polycarbonate instead of PLA/PETG? This would no longer require laminating with carbon sheets. If you google for “Introducing Javelin’s 3D Printed Hydrofoil Project” you will find a report from 2017 where someone printed a polycarbonate foil, but I haven’t seen results of their tests.

Hey mate, I'm pretty sure you'll still need to wrap the print with few layers of laminate at least for surface finish and impact protection. If you don't laminate it, the wing will be only as strong as the glue that holds it together. Someone on Thingiverse posted a wing printed out of ABS with some steel bars fitted lengthwise for reinforcement but this must be heavy as.

If you're considering making your own wing with help of 3D printer I strongly recommend looking into moulding described by PrfctChaos. 3D printing the mould is much easier than 3D printing the wing itself - for starters, you can print the mould from PLA because the mould strength isn't essential, it just needs to be stiff but doesn't really need any high strength. PLA is very rigid when printed with some reasonable infill and this is enough for good dimensional accuracy of the finished wing. Printing PLA is heaps easier than anything else I know and this is important especially with large prints like hydrofoil wings. I suffered from large warping at the base of my PETG prints which made gluing it together a nightmare. Also finding a glue that will actually stick to plastics like PETG is difficult, nothing holds reliably but I don't know about PC filaments.

I can imagine that printing with PC will pose some other challenges but the point is that you will make your life easier if you just make a mould of cheapest PLA instead of the printed wing of the high-end filament like PC.

[fluidity]

I have studied how to upgrade my Ender 3 to print polycarbonate, and this does not seem like too difficult of a task. Plus lots of success stories of others printing polycarbonate with, so I have good confidence that I can make it work.

True, the structural integrity is an issue: the Javelin hydrofoil was printed as one unit on a commercial grade 3d printer, but we cannot do that size print on a consumer grade printers.

I thought I would split the foil into 3 parts — just like most have done — but would insert round holes on one side and cylinders on the other side, as a part of the model. (or maybe make holes everywhere and print cylinders separately, might be easier as no need for printing with supports, etc). So when you connect the parts, the cylinders would go into the holes and this would align parts perfectly. With epoxy this should hold everything together. But completely unsure if this design is not going to cause a weak point on cylinders (or make the wing weaker) thus needing lamination and defeating the whole purpose of polycarbonate use.

I'm not sure what polycarbonate's shrink rate is after cooling? you might need to print it in an oven?
Otherwise re joining, I just show my wing transparent and place 3.6mm x 40mm cylinders across all the places I want to join later. Once I'm happy I subtract them from the solid of the wing and split into it's parts. Any flat chopped surface only has holes, nothing poking out so it can lie on the bed which it usually does end up doing. When finished I cut a hole lot of 35mm long bamboo skewer pieces and clean the holes out to 3.5mm. I test the fit, dissassemble, apply slow superglue and then reassemble. But I use PLA+ which works well for me. Only issue is that it is about 1.24 kg per litre.

PETg density is even higher at 1.38 kg per litre. However I'm highly unlikely to go under 25% fill and I only use 2 perimeter layers so the wing isn't too heavy and besides, it's immersed and will float after cladding on the sections I have used so far anyway. I use cubic infil and set the logical nozzle thickness wider than the actual nozzle diameter. This ensures tracks are pushed down hard onto the previous layer. PETg is recommended to print with a big layer height to allow the surface tension and thicker layer placed to flow nicely into the under layer but this is only possible if your wing doesn't change contours too sharply with bad overhangs in which case you'd need a dual extruder to produce suppots that could be separated easily from the PETg later. With PLA+ it still shrinks but I use a wide brim, typically 10mm around the base and that reduces lift at edges. Also I have recently found that trying to do all pieces at the same time gives more corner lift, it's better to build the model one piece at a time faster so the previous layers have less cooling time before the next pass. For my cubic infill I keep the speed and over-diameter constant between infill, internal perimeters, external perimeters, contained perimeters etc as this give more constant flow control with less under and over extruded parts. I also keep the layer height low enough to have good overlap on previous layers at the 45 degree upwards angles of cubic infill. After a non printing move it's common for there to be a small gap in printing as the flow pressure catches up, for this reason it's a good idea to go well past 10% on fill as you need any cubic cell surface voids to have a high probability of opening to a sealed cell. So cell voids should be no more than one per cell. A higher fill rate raises the cell sealing rate as any individual single infill track covers more cells but is unlikely to cause a void in more than one. A cell is comprised of many layers but voids are more likely close to the edges of the model where a non printing move has been performed. It's also possible to make all moves wiping moves which reduces nozzle leakage but I'm suspicious of the integrity of fast wipe move deposits, that they may be a source of poor adhesion. Anyway, it's certainly possible to make PLA seal very well, I've printed many dozens of PLA and PLA+ vases and only bad settings typically cause voids in outer walls. Beware that most slicers allow % settings on nozzle diameter that actually relate to % of nozzle diameter based on layer thickness. This can give bad results so I like to set absolute values instead of percentages. They are treated quite differently and it took me a while to prove to myself that my waterproofing failures were caused by a different response to my % settings than was logical.

[salvatoreone]

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

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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

Also in another reply, you mentioned calculations for a stab. Are you able to calculate the optimal stab parameters for the above wing?

[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).

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

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).

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).

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.

[salvatoreone]

Thank you! They are very close to each other indeed... I'll try the smaller wing with 700mm span just because it's smaller, this will be something completely different to what I have now so I'm very curious how it feels. Maybe also a touch easier to make since it's smaller. I just wonder if I need a buoyant board to take off. The one that I have is a flat board with not much extra volume but I'm sure it will be doable.

Ah yeah, I didn't even think about all these factors needed for the stab. I assumed it just lift*distance to CG but when I think about it there are so many other factors. Even the distance to CG isn't obvious because it depends on the foot balance. I'll start with the stab you recommended and then try different mast positions relative to the board and this should be enough to find a sweet spot.

[PrfctChaos]

I use a 95cm or 100cm long, thin board for all my foils (Wave, freeride and race). So I wouldn't worry too much about the board (A bit of nose rocker is nice though). But if you are used to much larger wings, then it might take a session or so to get used to the the higher take-off speed needed. It helps to not be underpowered and get up to a good jog speed (with board on the water) before lifting off, otherwise wing stalls and drops you back on the water. But you get used to it after a while and then just send the kite hard and get\straight onto foil at speed.

Yes the two wings are pretty close together. They have identical centre chord and just a bit reduced wingspan on the one. You can see the wingspan helping the 750 mm wing at the lowest speeds, as the speed increases the wingspan means less and less. So they end up pretty close together at the mid and high speeds.

[downunder]

Hi,
I am following this thread with a great interests. Lots of great info, thank you! I just got into foiling myself (on slingshot hover glide nf2) and thinking that at some point I might end up printing a different foil that would fit into slingshot fuselage.

Did anyone consider 3d printing a foil with polycarbonate instead of PLA/PETG? This would no longer require laminating with carbon sheets. If you google for “Introducing Javelin’s 3D Printed Hydrofoil Project” you will find a report from 2017 where someone printed a polycarbonate foil, but I haven’t seen results of their tests.

Hey mate, I'm pretty sure you'll still need to wrap the print with few layers of laminate at least for surface finish and impact protection. If you don't laminate it, the wing will be only as strong as the glue that holds it together. Someone on Thingiverse posted a wing printed out of ABS with some steel bars fitted lengthwise for reinforcement but this must be heavy as.

If you're considering making your own wing with help of 3D printer I strongly recommend looking into moulding described by PrfctChaos. 3D printing the mould is much easier than 3D printing the wing itself - for starters, you can print the mould from PLA because the mould strength isn't essential, it just needs to be stiff but doesn't really need any high strength. PLA is very rigid when printed with some reasonable infill and this is enough for good dimensional accuracy of the finished wing. Printing PLA is heaps easier than anything else I know and this is important especially with large prints like hydrofoil wings. I suffered from large warping at the base of my PETG prints which made gluing it together a nightmare. Also finding a glue that will actually stick to plastics like PETG is difficult, nothing holds reliably but I don't know about PC filaments.

I can imagine that printing with PC will pose some other challenges but the point is that you will make your life easier if you just make a mould of cheapest PLA instead of the printed wing of the high-end filament like PC.

Hi,

I'm trying to find the moulding process, where is it?

Thx