# Going down a rabbit hole - Parametric foil design and printable molds in Onshape
**URL:** https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227
**Category:** Build, Repair & Mod
**Created:** [September 23, 2026, 7:42am UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227 "2026-09-23T07:42:22Z")
**Posts on this page:** 8
**Page:** 2
### Author:  [@Jb69](https://foil.zone/u/Jb69)
#### Post date: [October 4, 2026, 1:27pm UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/21 "2026-10-04T13:27:33Z")
Fair point on the volume. I’ll keep this one short.
Agreed, the joint is the hard part, and it’s where most of my last week went. Short answer for now: the semi socket. The fuselage’s nose, or a flat bar on a home build, drops into a pocket molded into a hub on top of the wing, with carbon cheeks either side. The cheeks take the twist and the side load, so the bolts only have to hold it down. The fit is set in the mold, 0.1 to 0.2 mm a side, rather than by sanding. The next thing I’m adding is bolting it from the wing side, up through solid laminate into the fuselage instead of into inserts, as a lot of production wings do.
The longer answer is that I’m not trying to pick one. In a parametric tool the joint is a dropdown and a few dimensions, so the variations are cheap. What’s useful is having options that fit what people already own. Right now that’s a flat mount, the semi socket, a full square socket for a bar and a round tube socket, plus a production-style mount pad on the stab. Next is a joint that mates with Gong’s V3 fuselage, so a molded wing bolts straight onto a fuselage that’s already common. That one waits on me buying a V3 and measuring it.
Whichever joint, the tool works out the loads in a hard carve (3 g by default) and checks the laminate against them:
- root bending and the carbon caps
- core shear
- how much carbon is left under each bolt head
- the fuselage in torsion
What it can’t tell me is play and fatigue over a season, and you’re right that that’s where the bigger foils struggle. That takes someone building one and riding it, which is the next step.
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### Author:  [@Jan12](https://foil.zone/u/Jan12)
#### Post date: [October 5, 2026, 1:46pm UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/22 "2026-10-05T13:46:05Z")
I have been trying to get the stall speed of the AFS Silk 1050 and it is really hard to do.
Stall simply does not happen.
What I have figured out for my weight (95kg complete) is, 17.3 km/h is too slow. But I do not stall, but simply loose height over water until touchdown.
With constant pull I could probably set an AoA to stay up, but this would be a nonsense number with absurd drag.
So I think the minimum usable speed is around 18.5 km/h.
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### Author:  [@Jb69](https://foil.zone/u/Jb69)
#### Post date: [October 5, 2026, 2:43pm UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/23 "2026-10-05T14:43:08Z")
Thanks Jan, that’s the most useful number in the thread: a real minimum speed on a wing I’ve modelled, with a weight.
“Stall simply does not happen” is what the Silk’s tubercles are supposed to do. When I went through the published tubercle tests (Miklosovic’s humpback flipper model, Johari, Hansen, Bolzon), the one result they all share is the shape of the stall, not the numbers before it. The stall starts in the troughs between the bumps. Each bump sheds a pair of vortices that keeps the flow attached behind it, so the stall stays confined to the troughs instead of spreading along the span. The wing doesn’t drop; it runs out of lift gradually while the drag climbs. Losing height until touchdown, and being able to hold it with a constant pull at absurd drag, is that same thing seen from the board. The tool can’t calculate it: a lifting line and a 2D polar don’t contain those vortices, so it reports the tubercles’ effect separately, as a range.
Where your numbers bite is how early it starts. I ran the Silk 1050 in the twin at 95 kg (with my guessed sections, since AFS don’t publish theirs):
| Speed | Wing CL needed | Share of the section’s CL max | Board angle | On the water |
| --- | --- | --- | --- | --- |
| 13.2 to 13.6 km/h | about 1.2 | 100 %: the model’s stall | | never reached |
| 17.3 km/h | 0.74 | 57 to 61 % | 5.3 to 5.9° | too slow, sinks |
| 18.5 km/h | 0.65 | 50 to 54 % | 4.3 to 4.8° | minimum usable |
The ranges run from Ncrit 9 to Ncrit 1. So where you’re already sinking, the model thinks the wing has 40 % of its lift in hand. On this wing the soft stall sets in at about half the CL max a smooth section would reach. That’s the troughs, plus a real finish, the real sections, and a rider who isn’t a fixed weight, none of which the model has.
That gives me what I asked for back in post 3. For a tubercled wing like this one, the minimum usable speed is about 1.4 times the tool’s stall speed. Put another way, it’s where the take-off loading reaches 50 to 55 %, not the 85 % I’d been using as the limit. For an 85 kg rider on the same wing that’s about 17.5 km/h, where the tool quotes a 13.1 km/h stall. Your 18 km/h guess back in post 2, for a 1000 cm² wing at the same weight, lands in the same place. I’ll make your two numbers a check the model has to pass: at 95 kg on the Silk 1050, 17.3 has to come out below the usable limit and 18.5 above it. And I’ll stop quoting a stall speed for tubercled wings, and give the minimum usable speed instead.
Two questions, if you don’t mind. How were you riding it for this: winging, towed, pumping, or with a motor? It changes what “constant pull” means. And did anything log speed with power, current or heart rate? The model has the foil’s drag almost flat between those two speeds: about 40 N at 18.5 and 42 N at 17.3 for the wing and stab at 95 kg, under 60 N with a mast and fuselage. So if whatever was pushing you had to work much harder at 17.3 than at 18.5, that jump is the soft stall measured as drag. It’s exactly the part of the curve the model can’t see yet.
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### Author:  [@Jb69](https://foil.zone/u/Jb69)
#### Post date: [October 6, 2026, 2:33pm UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/24 "2026-10-06T14:33:28Z")
**A side branch of the rabbit hole: scanning a foil back into the tool.**
**The itch:** nobody publishes a wing’s section. The best you can do for a production wing is “a NACA something at a guess”. So I’ve been building a scanner that goes the other way round from the molds: photograph a wing, get the tool’s own parameters out, and from there tweak it, re-mold it, or just know what you’re riding.
**How it works so far:**
- An iPhone app that takes about 300 photos by itself as you walk round the wing, nothing to tap, nothing in your photo library. Depth sensors turned out too coarse for a section (LiDAR is a centimetre, the face camera a millimetre or two), so it’s photogrammetry.
- Printed AprilTag targets round the wing for scale and reference: a plate of tags, two measured bars, a cradle for the fuselage, and a printed NACA test section in every shot so each scan reports its own error.
- The Macbook rebuilds the 3D model, splits it into wing, fuselage and stab, slices it at stations and fits the tool’s section and planform laws, with an uncertainty on each number. It refuses what it can’t fit rather than guessing.
- A separate printed jig and the phone’s own tilt sensor for incidence, twist and decalage, which the photos can’t do to a tenth of a degree.
The check so far: a wing built in the tool, every parameter known, exported and run through the fitting with phone-photo noise added. It came back with the camber to 0.04 % of chord, the thickness to 0.05 %, incidence to 0.08°, the winglet’s angle to 0.2° and even the tubercles’ pitch and height.
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### Author:  [@Jb69](https://foil.zone/u/Jb69)
#### Post date: [October 15, 2026, 8:35am UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/25 "2026-10-15T08:35:31Z")
Update on the scanner, since the post above: the first real foil has been through it.
the foil on its cradle among the tag plate, towers and scale bars
Nobody publishes their wing sections, so the section in any model of a production wing is always a guess. Nothing stops me scanning the ones I can get my hands on, so that’s what the set-up is for. The printed parts are a tag plate, three tag towers, a cradle for the fuselage, two measured scale bars with a tag at each end, and the NACA test section that goes in every scan to show how good that scan is.
the printed parts
the app guiding the sweep with the auto-shutter: photos taken so far, the coverage ring filling as you walk round, torch and exposure lock
The foil was scanned twice, 351 photos with the app’s own shutter and 111 with Apple’s guided capture, both rebuilt on the Mac at full detail.
What worked:
- All 85 tags found, the plate lined up to under a millimetre, the scale from the bars to about 0.2 %.
- The wing’s sections come out to about 0.1 mm over the inboard half of one wing. The section isn’t a NACA 4-digit shape, so the fit goes free-form and writes a profile file the tool can take.
- The guided capture did as well with a third of the photos, and took a third of the time to process.
the scan at full detail: the foil cropped out of the scene (left) and the scene round the plate (right)
the same foil from the app’s own shutter (351 photos) and from Apple’s guided capture (111): the stab is better in the second
the fitted sections of the inboard half, normalised to chord, with two of them and their camber lines (only if this wing’s shape may be shown)
What doesn’t yet:
- The stab is too small and glossy for the whole-foil scan, so it gets its own close-up with a small tag cube beside it for scale. The app can do that now.
- The outer third of the wing needs a pass from below: the underside isn’t in enough photos, and the trailing edge comes out rounded.
- The scan’s twist disagrees with the jig by a few degrees. No idea why yet. That’s the next thing to chase.
Yes, a contour gauge would do one section. This does every station, the planform and the whole foil’s layout at once, and it’s more fun.
The point is the next step: the scan’s numbers go straight back into the model, which works out how that exact rig flies and then sizes the prop and motor for it. That last link isn’t proven on a real scan yet.
If anyone has a wing they’d let me scan, say so.
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### Author:  [@Jb69](https://foil.zone/u/Jb69)
#### Post date: [October 22, 2026, 6:40am UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/26 "2026-10-22T06:40:24Z")
**The molds are real now**
Until now every mold in this thread has been a picture of a Part Studio. This week one came off the printer.
the mold tiles printing standing on end
The timelapse is a stab mold printing as the tool exported it: five tiles, each standing on its spanwise end with the flat cut face on the bed, so every layer draws the whole section and the nozzle runs the cavity in one smooth pass. You can see the keys and pins on the flange faces coming up as the tiles grow. PLA, 0.2 mm layers, five walls, about 30 hours for the set.
the two halves, coated and partly flatted
Then the prep, which is where the time really goes. The photo shows the two halves glued up from their tiles:
- Left, the half with the mount pad: the recess for the pad with its two bolt cones (the holes are molded undersized and drilled after cure), and the dowel holes in the flange.
- Right, the other half: the matching pins, the pinch-off groove running all the way round the cavity to catch the flash when it’s clamped, and [the two raised bosses opposite the bolt cones: say what they form].
I’m following Easy Composites’ videos on directly printed molds for the prep and the layup. Every FDM layer has a small undercut, and resin cast against it locks the part in like gear teeth, so the layer lines have to go before any resin touches it. I’ve sprayed it with high-build automotive primer, the blue, and started flatting it back: the patchy areas in the photo are where the sanding has broken through to the high spots and the coat is still filling the lows. Next is flatting it down to 3000 grit, then a coat of epoxy, sanded and polished, then wax and release before the first layup.
What I learned from the printer side: [one or two real lessons, e.g. brim, a tile that lifted, fit of the keys straight off the bed].
Next post should be the first carbon part out of it, and with it the first real check of the tool’s layup numbers, the pinch-off groove and the release. If you’ve prepped printed molds before, I’d like to hear what you’d do differently before I lay it up.
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### Author:  [@S\_Roger](https://foil.zone/u/S_Roger)
#### Post date: [October 22, 2026, 11:01am UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/27 "2026-10-22T11:01:19Z")
@Jb69 Ive enjoyed seeing the extent of your AI assisted work flow (though I didn’t have time to read through all 6 miles of posts!).
Excited to see how things go now as you start making parts!
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### Author:  [@Jb69](https://foil.zone/u/Jb69)
#### Post date: [October 22, 2026, 11:42am UTC](https://foil.zone/t/going-down-a-rabbit-hole-parametric-foil-design-and-printable-molds-in-onshape/27227/28 "2026-10-22T11:42:40Z")
Thanks, I am pretty excited to make some parts too. fitting it in around work and getting wet is the issue.
The 6 miles, maybe 10 miles of posts is the entertaining part, seeing if it all works is the exciting part. but it is all coming together in about 5 different projects
I am also printing and testing my own props and collecting data via the Apple Watch app I wrote
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