A.L. Spinz

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I have a very limited knowledge on scratch building anything, but I have all winter to find out. So here goes. I've design my own plans and now want to start building. I have carved out the basic shape of the fuse, and it's almost ready for sanding and prep. I want to fiberglass the entire fuse, and I think I remember reading somewhere about using lacquer thinner to remove the foam from the fuse so that it is hollow and structurally sound. Please give your input if you know what I'm saying. How many layers of what oz. fiber cloth with who's epoxy? Thanks!

A.L. Spinz

BMatthews

Any LAMINATING epoxy will work. West is one type but if you check with the local boat building supply houses or a specialty figerglass supply outlet they should have the correct resin. And acetone or lacquer thinner should do the trick. You can also chew out much of it through the wing opening first to save on the amount of solvent you need to use.

Another method would be to build up a "box" of foam with some of the basic structure and control pushrods inside and sand the outer shape and glass that then leave the foam in place as a stiffener. That way you can get away with a lot less cloth. Probably half or 2/3 what you would need otherwise. Otherwise you need more so that it's self supporting.

Not having made a glass fuselage myself I'll leave it to others to recomend how much and what weight of cloth.

cappio777

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A.L. there are other methods a lot cheaper and with about the same results. Once you are done with the shaping of the fuselage you can wrap it with kitchen plastic wrap and give it a nice coat of releasing agent, you can also use cooking PAM spray but leave a very fine layer by spreading the film around. Now you dont have to use epoxy resin which is more expensive, about three times the price of polyester resin. Since the plastic layer wont let the polyester resin eat the foam just cover it with the fiberglass cloth and apply the resin for semi fast setting. If you allow it to dry slow and use PAM then it might soak in the cloth and will remain sticky on the inside. Depending of the size of aircraft you are designing thats how you should pick the cloth weight. For small 1/2A size birds try to use 2, 2 oz, cloth....for 40 size aircraft 2, 4 oz, cloth and increase it on the same pattern for larger aircraft. In the past I realize that if you cut your foam fuselage where you want the bulkheads to be, then add bulkheads and glue them, when you glass the fuselage and melt the foam with acetone the bulkheads are already firmly in place. This is a must sometimes if you are doing a ducted fan body. Oh, do not get rid of the foam until after you have finish the surface as smooth as you want. It would be harder to sand a semi-flexible body than a rigid one.

[sm=bananahead.gif]

[email protected]

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The foam we commonly use is the blue or pink which has a finer grain and seems to sand better than than the stryofoam. Usually available in 3/4" and 1", just laminate it with water based contact cement. More expensive than the stryo but it doesn't ball up as much. Drywall screen sanding sheets work great in sanding all sorts of foam. Tried the acetone and lacquer thinner many years ago and it made a huge mess and left the fuse pretty weak and not as stiff as it should be. Leaving bulkheads in (as above) and pre-installing the controls, engine mounts, lg and servo trays (think backwards from normal kit) and leaving the foam in now. Not really that much heavier and very much stronger. Saved my bacon on several not so pretty landings. Can't stand the smell of polyester so we use epoxy slightly thinned with denatured alcohol (keep stiring) which sets up slower as the internal reactions of the epoxy are slowed somewhat. Marine laminating epoxy at home depot seems to work well. There are many others but it is locally convienient. P.S. Don't get discouraged. We trashed serveral plugs and fuses before we got it right.

A.L. Spinz

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Thanks for all of you're input. Something new to think about. The fuse is a 48" f-18. The suggestion of the pre-installed bulkheads is a good one. This is my second attempt on the fuse using pink foam and I have a really good start this time. Just dont wanna wreck it by not doing the proper research. I intend to use DF set-up with tailerons to keep things simple. Doing the drawings were alot easier than the building. Any other suggestions I need to be aware of? So two laminated layers of glass will be sufficient, given the correct weight/oz. cloth?

checksix

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I've had good results using by using packing tape over the foam. Then apply the glass with laminating epoxy, sanding and smoothing between layers. When you're happy with the results, the fun part: pour in acetone or gasoline to dissolve out the foam. The packing tape serves two purposes: it reduces the amount of epoxy needed (hence weight) and prevents the solvent from softening the glass/epoxy. The final step is to peel the packing tape off the inside of the fuse. Try it out first on something small. Its fun and works great.

--Derek

cappio777

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Just as Checksix mentioned, the idea of covering the foam with some kind of plastic is to reduce the amount of weight from the foam soaking resin. If you design it properly enough for a DF model, the packin tape or plastic wrap would leave a smooth surface where you might not have to use thrust tubes at the exit. As far as leaving the foam inside I wouldnt recommended, on a fuselage that size you could have up to an extra 12 oz just on foam alone. No choice in the matter if its a DF model. If you want the model to last longer and withstand the "old probable" hard landing I would recommend 3 layers of 4 oz. Keep each layer on the borderline of wetness....too much resin and it adds weight and also tends to crack easily.

A.L. Spinz

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Cappio & Check,

Thanks for the input. Yeah I was thinking that keeping the foam inside, other than for DF reasons, would be a bad idea. The foam plug, even sanded with as much material removed, weighs a ton...add glass and epoxy on that with a 33" wingspan (not much wing, at all) and I'll have a pretty fancy brick or static display of a F-18. Well you guys have restored my confidence. Sanding is almost completed. The three layers of glass sounds good...will that make the airframe fairly rigid? I also imagine strips of glass here and there wouldn't hurt, reinforcing the critical areas. I plan to have access hatches at the canopy area and the mid-to-rear portion of the fuselage, I guess when those are created I could add a few 1/8" lite-ply bulkheads or should being be thinking more coroplast type material (I guess that's what its called).

BMatthews

You didn't mention this was for a smaller model. You may want to weigh all the components and forecast some resonable weights of the structural parts and see if you're painting yourself into a corner.

If the foam is already feeling heavy then leaving it in is not a good option except perhaps for aditional stiffness in a few areas. With a 33 inch F18 I imagine the wing area will be around 400'ish sq inches? If so then about 3 to 3 1/2 lbs is as much as you want to go. Lighter if the wing is smaller than that. Of course you're fighting the usual scale model situation. Too much model and not enough wing. Because of this you may want to use the leave foam in place method and use a lighter glass layup. With the foam in place it doesn't take much to be strong. In this case perhaps two layers of 2 oz with a third layer of patches in key areas.

One item if you have not done much glass work. Resin is heavy, resin is the enemy, use as little resin as you can in the initial layup. Just enough to make the cloth go transparent. Ignore the weave showing through. After it's cured fill the weave with a second coat of resin with microballoons (those are lighter). Then primer, sand so it's almost gone, primer, wet sand to smooth and paint.

Good luck.

michpittsman

My Feedback: (11)

Bruce-We always think fiberglass is the only way to go; reading the British model mags occasionally I see a lot of models built with very light foam with a skin of kraft paper/white glue (brown paper bags to us), with or without internal wood structure. Can you say "dirt cheap"? Be aware, some kraft paper is waterproof. This has always seemed like a noteworthy method to me; maybe someday... JIM ... SO MANY AIRPLANES, SO LITTLE TIME