Blue foam fuselage
 

I want to make a fuse for a large pattern plane. I have a bunch of blue builder's foam. I would like to make the fuse in halves. My plan would be to, stick two pieces of foam together with double stick tape. Bandsaw out the profile. Carve what I want. Carve out the inside leaving 1/2" walls (adds rigidity at a low weight). Add internal parts. Stick it back together. Glass with polyester resin and glass cloth. Bondo sparingly.

Does poly resin eat blue foam? I want to use what I have. If need to buy stuff (epoxy resin) I might as well stick build it out of balsa. Besides I have found epoxy resin to be more difficult than poly resin. I suppose could also buy a pile of florists' green foam for my core, it is cheap.

RE: Blue foam fuselage
 

Polyester resin will eat Dow extruded polystyrene foam.

What epoxies have tried before to do laminating?  A good epoxy laminating resin is very easy to use.

RE: Blue foam fuselage
 

That is beginning to sound very heavy. There are many ways to skin a cat. When I do one off parts and the process allows, I make fiberglass parts using the foam as a male mold. You can carve the shape you want from foam. Cover with mylar packing tape, apply a couple coats of carnuba wax. You are now ready to apply fiberglass cloth and resin. If you seal the foam well enough you could use you polyester resin but will end up with a heavier part. There are many variations of this you could do. You could employ a core material to stiffen the structure but thus would require you to vacuum bag. For a fuse you would fay up the glass, let it cure and then sand smooth while still on the foam mold. Trim the seam, pop off the form and then lay up the other side. Once you have two halves you can tape them together from the outside and seam them together.

RE: Blue foam fuselage
 

You can also just melt the foam out with solvent and then peel the packing tape out.  This way you don't have to make a seam.

There are some new foams that are water soluble.  I was just a testing lab that CNC cut the foam blank, ran it through a braiding machine, vacuum infused the braid, and then poured water in through an opening to melt out the foam.

RE: Blue foam fuselage
 

I have been using two part epoxy from the craft store. It is obviously junk. I live in a technical wasteland. One can get poly resin from an auto parts store.

My idea regarding leaving a layer of foam intact is based on observation. I have made cowls by laying cloth over a foam plug. Even the thinnest cloth layer over a foam plug is really strong. Remove the foam and it is very frail. Why not leave a little foam in place as a stiffener?

RE: Blue foam fuselage
 

Get WEST System epoxy;


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RE: Blue foam fuselage
 

You could use polyester but need a barrier like the tape, or white glue/water mix. It would be heavier. I tried it once and it still ate through in a few places. There is also water based polyurethane instead of polyester (WBPU)and fiberlass cloth. Not as strong as polyester, but cheaper than epoxy. Just throwing it out there. I wouldn't put a lot of time in it in case there is a learning curve, or it doesn't work. I think the pink foam is lighter. Never heard of the florist foam being used. Is it compatable with the polyester?

RE: Blue foam fuselage
 

I think leaving as much foam in place is a good idea. The foam can really offset the buckling of the skins. If the weight is equal, between leaving the foam or taking it out, you would use a little less glass to offset the weight of foam. The skin would be less pucture resistent but the structure will be stiffer. If you glass the inside of the foam structure it will become even stiffer.

RE: Blue foam fuselage
 

OK, west marine epoxy. What weight glass cloth for a 1/4 scale. Sanding the epoxy and filling imperfections, what is the correct epoxy that can be sanded, how about filling little holes.

RE: Blue foam fuselage
 

You can sand West Systems resin. You can fill larger blems with bondo or a mixture of epoxy laminating resin and micro-balloons. Little pin holes can be filled with a mixture of micro-balloons and primer (single component stuff like Dupli-color Paint Shop)

RE: Blue foam fuselage
 

I did my 1st foam loss method using Bondo brand polyester resin from the local auto parts store over pink foam. Scaled up a Brian Taylor Bf109E to 81" ws. Framed and filled between the bulkheads with foam and hot wire cut following the fuselage formers. Repaired my bad hot wire cutting with light weight spackling and sanded. Covered with econokote ( low temp so as not to damage the foam ). Trimmed the econokote off at the formers so the fiberglass could stick there. Should have waxed the econokote but didnt ( lessons learned ). First layer of cloth was .5oz to keep cure temp at a min. Then 2 layers of 2.7oz. Removed foam using acetone then gas ( outside of course ) messy. Let it dry and it pealed out easy. Made a light weight and strong structure.