Pink Foam, Fiberglass, and Casting, Questions!

LizardJedi

LizardJedi

Sr Member
OK I have to say first off, that I've been searching around a reading a lot of old threads about this, and I'm learning a lot. But this will be my first time playing with this kind of stuff, and its a big group project, so I can't screw up!

Long story short, we need to make some airplane wings. Each wing is made up of 2 parts (so 4 parts total) and size wise, the biggest part is about 3'x1'x1.5"

I know there are way that RC people do their wings, but we're starting totally from scratch here.

I came up with a couple ideas, and I would like some input on how I can refine them to be most accurate, and maybe some guidance to if they are even possible (or feasible enough to do)

Since I needed to sketch these up anyway, and because its a lot easier for me to explain things, I snapped a picture of my sketches (scanner isn't hooked up ATM)

Sorry for the bad penmanship...
IMG_0145.jpg


So, it break it down..

1) CNC the wing out of pink foam. Seal it (latex paint?), then lay some fiberglass over the top. Somehow the FG has to be smooth and even on top... so I guess vacuum bag the FG?
Then, we can either use it as is, or I suppose we can make it hollow, and get rid of the pink foam with some laquer thinner to dissolve it out.

2) CNC a negative mold for both sides out of wood or MDF. Seal this (with paint?) and tons of mold release. Use this as a fiberglass mold. CNC some supports out of metal or carbon fiber (or whatever else we have laying around).
What I don't know about this method is if we would have to glass each mold seperatly and then join them after they cure, or if we could sandwhich them together with the supports, as shown in my sketch. I have a feeling we would have to do the former?

3) Just a mix of 1 and 2... make both a negative and positive mold, glass the negative mold, put the positive molde inside, and sandwhich together (the supports could be included, if the positive was made out of sealed pink foam in sections, with the supports attatched.)

I also had an idea with the negative mold to vacuuform styrene in it (which would probably give the smoothest finish) then glass the styrene. But the vactable we have access to isnt that big. Cutting in sections is an option (in my mind) but the other people in the group don't think its strong enough.

The most important thing in this whole operation is how smooth the surface is. Spending all of our time filling and sanding isn't really an option either.

Time is also of the essense. Honestly, I'd like to try all 3 ways, but this has to be done yesterday. :unsure

So, you glassing and casting Gods of the RPF, help me figure out what to do!
 
First, if you can avoid CNC I would, unless you have a big budget.

If your wing is a simple shape you can use templates at either end and run a hot wire along the templates to get the shape.

If you're going to glass over foam I would either, use a urethane foam (but again expensive) or if you're going with pink foam, I would use epoxy on the first layer or for all the layers.

I don't know how strong the wing needs to be but glass over foam is going to be very strong, so I would leave the foam inside.

With pretty much any method you choose your going to have to spend time sanding and filling, either the part being glassed or the negative mold.

Also vacuum bagging is going to leave a texture from the release film that will need to be sanded and possibly filled.
 
We have access to CNC machines, so the costs there aren't really a factor.

The problem with the hot wire was that we don't have access to one. Well, a big-enough one.
 
Is there a picture above? If there is, it is filtered here at work.

A wing? Will it fly? Will it support weight? Is it just for looks?

Without any knowledge of the above, it is hard to say what the best method is, but I have made lots of wings for RC planes. The standard wing is hot-wired EPS foam with telpates as mentioned above. You can build a hot-wire set up easily. The foam wing is then laminated with thin wood veneer and sealed with lacquer.

If this wing isn't going to fly, then the airfoil doesn't matter, and you can sand the foam into shape.

My last suggestion is that if you need it to be fiberglass, don't fiberglass over pink foam, it will dissolve.
 
Yeah there's a picture, its hosted on Photobucket, that might be where its being blocked.

Yes its going to fly, and yes it has to support weight. That's one of the reasons I'm a bit concerned about smoothness.

I learned this morning that apparently they're going to try and get a hot wire set up.... but they've been saying that for the past month and nothing has happened. Which is why I've been looking into alternative options.

From what I've read, if you seal the pink foam (with a few coats of latex paint, or something similar) you can then glass over it? Does the EPS foam not require sealing?
 
do NOT glass over the foam, especially if you want it smooth. After you glass over it, then you gett o sand, putty, sand, putty, and sand some more. Sanding fiberglass for hours can ruin anyone's day.

If it is going to fly, then it might be a good idea to build the wing like a real wing, wing ribs on a spar and covered in monocoat.

If you are dead set on a fiberglass wing, then once the foam has been shaped, either by hot wire or sand paper, then vaseline it and make a quick plaster (hydrocal) mold. Seal the mold well, and lay your fiberglass into the mold. If it is going to fly, you will need ribs and a spar.

Is this a flat bottom airfoil, or a curved bottom air foil? The only difference will be how the plaster mold is made.

Depending on how strong this needs to be, My first choice would be to Monocoat the foam directly for a smooth with. Second choice would be to give the foam a wood veneer. Those are the quickest wings. Beyond that, you are building an airplane wing, and it must be structurally sound.

Maybe, after I get home and see the picture, I will have a better idea.
 
Why not just build it like a real wing? Ribs for the shape and a skin glued on top? Probably be easier.
 
Szyntax said:
Why not just build it like a real wing? Ribs for the shape and a skin glued on top? Probably be easier.
Click to expand...

The skin has to be a structural member. Which is why I was thinking fiberglass. If you notice, my second idea is basically what you're saying, but casting the wing first then adding the ribs on.

C6 - Yeah I'm trying to avoid the sanding/filling scenerio as much as possible. (which is why I'm not a big fan of the vacuumbag idea)

The more and more I think about it the more and more I like the idea of vaccing the skin out of styrene and then glassing the inside of that, and adding supports, but thats probably going to be just as much work.
 
I remember way back when I did aircraft models for NASA, the pieces were machined in hard foam. Then we carefully sanded the stair-stepped ridges down with a 220 grit sandpaper, finishing with a 320 grit sandpaper and finally coating the surface with an actual resin, not fiberglass, but a hard resin.(damned if I can't remember the name of it)
But the way we put it on was with a squeegee, and we slowly spread it out from the center to the edges. This was a slow hour long process, but in the end, all we did was re-sand the surface with 320 grit sandpaper and we were ready for painting.
I think if you go for the low density hard foam (yellow or green?) that would be light enough to stay in the wing. But again, these were models, and not actual flight parts.
 
You can fiberglas over the pink foam, but have to be really sure it's covered with a non-permeable barrier, such as masking tape or aluminum foil. If you're going to make multiples, have you considered a fiberglas negative to make fiberglas positives out of? That way, a large mold wouldn't be so heavy. Just be sure to wax the negative, buff it, and spray on a pva release.
 
OK, I missed the 2" wide part. This is essentially a yard stick.

So I will stay with the idea to hot-wire or sand your foam piece, and go to a model airplane store/site and get some veneer plywood (1/32") and give it a skin. Use balsa for the wing tips, and seal with dope. No reason to fiberglass or CNC.
 
If it were me, I'd sculpt the wing out of automotive clay, and use true sweeps to guarantee eveness of the curve. True sweeps are very hard to find these days, as the method of sculpting cars by hand has given way to computers, and machines. Then I'd make a mold, and cast it. Have cut, sanded several types of foam, - beadboard, superfoam, etc.. and I hate it. stuff goes everywhere, vacums up, but gets on everything, and everyone. clings. baby powder helps, but...
I also can't stand grinding, and sanding to much. way too messy for me.
 
I've done several sculpted foam pieces using regular/eps foam, all you have to do is get a barrier coat on it, simply put, latex house paint with no toluline(sp)
Also, if I recall, epoxy resin doesn't melt strofoam, it's the polyester resin that does that, test the theory on a small piece, can't hurt to try...


Will
 
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