I came across this set of photos which shows some interesting processes as far as EPS/hotwire cutting, female moulds, wet layup using moulds, carbon spar (stringer) reinforcement, and honeycomb sandwich construction.
I’ve seen similar methods used in conjunction with vacuum bagging and resin infusion with carbon for better resin/glass ratios and weight savings.
Thought it might spark some ideas for the hollow/sandwich construction set.
Interesting stuff… but some captions would surely help.
What is the material of the wing ribs? Seems like a hollow/cellular structure…?
I’m pretty sure it’s aluminium honeycomb sheet.
Cheers
Rohan
No fuel in those wings? Where will they put it?
Here’s another interesting composites site. A few more details about some of the processes…
http://www.quatrocomposites.com/comp101proc.htm
But I’ve been obsessing over this female molding idea. Why would you need to lay it up wet?
Couldn’t you build both halves of the mold, just like they did, but surfboard size…print your cross sections of board every 6-12", trace them onto plywood, split them in half & cut them out. Use each sequential pair of plywood half-cross-sections as hotwire guides for blocks of EPS. Once cut, glue them all together in proper rocker…
Paint the insides with mold release. Lay on a couple layers of CF cloth, already wet out on a table. Then lay on some peel ply & paper towels. Poke the whole thing into a vac bag & pull…pop it out, do the other half. Pop the halves out of the molds, grind the seam, lam them together with CF tape & epoxy…
What else would you need? Everything seems completely do-able. Or am I missing something?
Even 1/8" d-cell between 2 pre-wet sheets of CF. That would be strong enough, right?
Before you join them together, you laminate in a block of d-cell surrounded with CF - even in the vac bag would be ok - that will hold a finbox you’d router in later from the outside…thicken up a little place to install a vent screw…
All of a sudden it doesn’t seem so hard. What am I missing?
I don’t think you’re missing anything Benny. It is all very do-able as you have described. Would love to see you give it a go. You could also try the prepeg carbon fibre in the mould and popped into an oven - sometimes the aircraft companies throw out their prepreg sheets after they have passed their use by dates (I’m sure they would still be OK for surfboards - just not aircraft). Pope “stealth” bisect is a hollow carbonfibre job isn’t it ?
Cheers
Rohan
“All of a sudden it doesn’t seem so hard. What am I missing?”
Not much, that’s pretty much the process. About the only thing you’d need that you didn’t mention might be some internal stiffeners, like the wing ribs in those photos. You’d have to play with it a bit to get the flex where you wanted it, but maybe run 2 or 3 lengthwise like stringers from nose to tail, that would keep the skins from compressing so much. It’s basically how they make the Salomon boards. The only downside is the labor intensive process of making the female molds.
Something I thought about when I was looking at the pictures though, is that you’re making the board from the outside in, as opposed to working from inside out as with a typical blank then glass job. Where that seems to really be a benefit is that you could get a finished outer resin coat if you vacuum bagged it. Almost like a gel coat, but if you got your ratios right, it would be quite strong and very light, plus no worry of sand through or gloss coating. As I thought more about it you could do balsa skins like that. Lay up all the strips, cut them to shape, then bag them with the exterior glass face down on smooth flat surface (glass, formica, etc.) then use that pre-glassed balsa panel and glass it onto the blank using the interior glass and resin to bond it to the blank. By doing this you’re also pre-tensioning the exterior glass job and you’d be able to heat-cure the exterior glass and balsa with no worries about the foam core since it wouldn’t be attached yet. I hope my rambling makes sense.
That’s kind of the reason why I posted the link. It shows a process that is proven and has lots of relevant processes to non-traditional surfboard construction.
Something else you could do with female molds though, is shape a slightly oversized blank, a plug if you will, and make the molds from that. Use a sandwich core material, d-cell, xps, eps, whatever, but put it against the mold almost like a rocker table then put the glass on the inside then bag it. The glass would hold the mold shape into it. Make both sides like this then join them without exterior glass and you’d have a shapeable blank that you could tweak a bit depending on how thick of a core material you used. Once shaped then just glass as normal. Labor intensive but you’d be able to make more than one specific shape out of a set of molds that way.
Sorry for the rambling, one thought leads to another.
edit: spelling
Yeah, Lawless, all those thoughts are coming to me too. I actually figure that the way to go is to make the top & bottom female molds & then bag in a layer of glass without mold release, so you have a nice stiff substrate to work off of. You paint in your mold release for subsequent production molding…
The neat thing about that is you could then tweak contours with a contour mat like Bert uses. Want a concave? A double-barrel? A step-deck? Done. Want to mold in a swallow tail? No problem, just add a triangular chunk of foam to the mold. I mean, its obviously not as easy as that, but I’m sure you see what I’m thinking…
I think I’ll have to give it a spin.
Lawless…
The process you have described is basically how I build the hollow carbon fiber board. There are some challenges to the process and techniques, but you can build a very strong sandwich shell, and keep the weight down. Give it a try.
Good luck with the process!!
Ken
Thanks for posting that. Also on that site is much more of the building of that plane for those that might be interested.
Wow, that’s a large hobebuilt airplane. I’d go for something more simple, like this http://www.cozyaircraft.com/
regards,
Håvard