Seeking advice on fiberglass wingtip build process

[MidGenerationAL]

image.pngPictured above is the 3d model for my wingtip mold. I divided it into 24(!) pieces and started 3d printing the parts of the mold.
It will take about 30 days and $300 worth of filament to print each mold (right and left). Neither time nor cost is prohibitive, but both are annoying.
The alternative would be to print the wingtip itself as a dummy and pull a mold off of that. Much faster print, much less material.
One possible advantage of a 3d printed mold would be the ability to assemble it and take it apart in multiple different ways. Eg, for the tight spots, I could start the layup using only the relevant parts of the mold, then add on the other parts of the mold. Ditto for taking the mold apart.
The main advantage of 3d printing the plugs then pulling a molds would be that the parts can be permanently glued together - after some filling/sanding/priming there would be no concern for aligning the seams or the seams showing.
I have been through the process of 3d printing plugs/molds for fiberglass layups but this is far and away the largest and most complicated such project I have tried.
Would appreciate any advice or suggestions.

[jaredyates]

I sometimes encounter a problem where I try to employ the less-optimal tool for a job and end up spending more than I would have if I had instead hired someone with a bigger tool. Like I could dig a pond by spending spend 100 hours at $100/hr with a tractor or hire someone with a bigger machine who can do it in 10 hours at $1000 per hour. At first glance that may sound like an even-money proposition, but there is 100 hours of my time that isn't accounted for, and also the likelihood that I'll break something and have to fix it. And the job gets done in two days instead of two weeks.

Is it worth looking around for someone who could CNC foam or some other material, or even find someone with a larger 3d printer that could provide better value? Even if you were spending, say $500 I wonder if you'd be ahead.

Lately around our house the 3d printer has occasionally been the hammer in the "every problem looks like a nail" proverb. I've been studying printing male molds out of water-soluble PVA for one-off duct fittings and such.

[noema]

Did you get some quotes from any of the prototyping services. If not, might be worth checking out.

Some I know, but there are more:

Xometry: https://www.xometry.com/cnc-machining/

3ERP: https://www.3erp.com/large-format-cnc-machining/

Star Rapid: https://www.starrapid.com/services/cnc-machining/

Protolabs: https://www.protolabs.com/services/cnc-machining/

[geraldmorrissey]

Not knowing much about 3D printing and based on my experience, a few thoughts. I would mock up the part and build a split mold around it. I would design the mold with the fewest mold sections, and as simple as possible, two tool sections if you can do it. Part geometry concerns like draft issues and pulling directions would be my first area of investigation. Can I assemble and dismantle the mold sections. Where the possible jig locks. Can I get the part out of all the mold sections. What indexes the mold sections together? I would add stiffening flanges a few inches wide around the periphery of the mold. Maybe mold in some threaded steel inserts for bolting the sections together. Try to keep the outside of the mold as smooth as possible in case you cure your part under a envelope vacuum bag. I have found after many years of trial and error that plaster and hemp fiber make the best molds for small quantities of parts that can be cured at temps up to 200F. But I'm old school. There's alot on the web about it.
Gerry
Patrol #30

[Battson]

Don't underestimate the time and cost involved with making a good pair of molds, or with cleaning up parts made from a bad set of molds. Molds are generally for medium to high volume manufacturing. You just need one of each part?

There's a lot of time, work, and materials involved with doing molded parts properly, especially if only for a production run of one (each side). You have to make six parts - producing 2x plugs, then 2x molds, and then the final 2x parts. Unless you genuinely plan on making several copies, then it isn't worth the effort in my opinion.

We made a sacrificial plug and made our parts over the plugs. Once we were finished we destroyed the plugs leaving just the parts behind. You can't avoid spending time and energy getting a smooth final shape and making the structure. Might as well work directly on the finished parts, rather than including several extra steps into the process, each adding more work (unnecessary work?).

Personally, I would 3D print a frame and make the finished parts over that with fibreglass (or carbon if you prefer). If the frame is light it could stay in there, or you could remove it afterwards.

[noema]

Mostly agree with Battson. Doing layups on on-time foam plugs is a good middle ground. I have built quite a few parts for my Bearhawk this way, including the instrument panel. You can even vacuum bag them for better strength to weight. If you use a foam plug, either cnc machined or hand-made, you don't even have to worry how the get them out of the part, simply dissolve with acetone.

https://noem4.com/xhawk/log/Instrument+Panel

[Nev]

I made foam plugs for my wing tips - cut to shape with a hot wire using a ply template already cut to the shape of a rib. Graham Johnson had done his this way, and loaned me his hot-wire. The foam was then covered with dry wall plaster and sanded to smooth. I applied packing tape over the foam mould (has a release agent on it), and additional wax just to be sure. I also added some flat aluminum at the wing tips to keep the aft join separated to ensure it could be removed from the mold, and also because I wanted to get a good fit by doing the final glue-up of the trailing edge joint in situ. Peel ply gives a pretty good finish which I was happy enough with and didn't bother sanding further. Once I was happy with the fit I then glued the aft edge and trimmed to fit. Kept the molds and they are re-usable.

The final fit on the aircraft wing is excellent, no wavey-ness, no gaps. They're also very light, and robust. I did add extra fiberglass matting to certain areas for stiffness and a tape along the edges. Overall I'm very pleased with the results.


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[geraldmorrissey]

If you mold to the inside of a part, IML (inside mold line) you must do a fair amount of sanding and filling to get a good surface finish on the exterior of the part, OML, (outside mold line). Why not spend that time building a decent set of cheap disposable molds to OML, having very little cleanup on the finished laminate. It's a trade off, but I hate sanding and filling. Plus it's an easy way to lose control of the finished exterior surface contour. If you have an accurate male mockup of the part, the hard part is mostly done, Just my .02.
Gerry
Patrol #30

[Bcone1381]

I started on my Hoerner style tips last week and am making it exactly like Nev did. The basic foam layup and cut with the hot wire can be done in about three hours each tip. I expect test flying will interrupt the wingtip build.

[Battson]

It's the sanding and filling you want to watch out for, if you're tracking hours I spent about 14 hours total, on that task. More with paint etc.

There's a lot more work between the second last photo, and the last photo!

Credit goes to Jeff Lange, who did this 13 years ago and made a detailed YouTube series for us to imitate and learn from:

[Bcone1381]

That is the video I used to teach me how to cut the foam.

[svyolo]

I have only hot-wired the white styrofoam. I don't know how well the pink or blue insulation foam work with a hot wire, but I sure do prefer using those to make molds if I can. You can shape them quickly with almost anything - rasps to files to sandpaper on a board. I usually just use spackle to smooth and fair them. Super quick and easy.

I think the Rutan style constructions uses foam similar to the blue and pink insulation, so I am pretty sure it hot wires just fine.

I have CF tips that I bought with the kit. They are super light (1 layer), but fitment is definitely an issue. I have always admired Steve Wittmans' wingtips from the later version of the Tailwind. I might give that a try for my B.

[Battson]

The hotwire works great on the higher density foams, like extruded foam boards. Everything happens more slowly though, so patience is required. Rushing it causes the wire to drag in the middle of the board, and that can lead to minor discrepancies in the shape.

[whee]

Our foam plus were high density foam. The hotwire worked great; like Battson said, take your time.

If we had use the foam and plugs to make some set like Battson and Nev have suggested here I likely would have been successful years ago.

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