Cox Engine And Foam Control Line?

NEW222 Thu Feb 25, 2016 9:28 pm

So, I have this big question that I am wondering if anyone may know the answer to. I have the plans for a couple of Dick Sarpolus designed airplanes. I have a good supply of foam here and was thinking. If I was to build a plane out of foam, and fuelproof it, does anyone think it is feasible? The changes I would be doing is making the wings from 1/4" foam, double up the fuselage from 1/4" to 1/2" by laminating two pieces of the 1/4" foam, and tail would also be 1/4". Among the other changes would be to add at least 1 piece of 1/4" square balsa as a leading edge on the wing, and if needed, the tail as well (basically doubling the sizes of balsa indicated on the plan). So, does anybody feel that this would be a worthwhile project, or should I just scrap this crazy thought. Thank you for any opinions and or advice given, both good or bad.

pkrankow Thu Feb 25, 2016 10:09 pm

Foam wings, wood fuselage if going for a profile. Use wood spars in the wings. If you design well there is no need for proper ribs. Been done by others.

Use a low temperature film to fuel proof the foam. If your foam is solvent tolerant maybe spray adhesive and no heat. Thinned white glue is supposedly fuel proof and exhaust proof, but I haven't tested this myself. Paint the exposed wood.

It is possible to go almost all foam in a full fuselage design, using plywood for the needed spots.
http://stunthanger.com/smf/building-techniques/the-bluefoam-model-or-how-to-build-a-stunt-plane-without-a-bit-of-balsa/

Foam is not stiff enough for a profile fuselage.

Phil

NEW222 Thu Feb 25, 2016 10:21 pm

Thanks. This is just what I was looking for.

PeterJGregory Fri Feb 26, 2016 8:56 pm

Sounds interesting - if you can continue reporting on your progress that would be great...

Edit - just thought about it, this might be a good use of the four miles of doculam I bought, for fuel proofing foam on a plane like this.

NEW222 Sat Feb 27, 2016 12:00 am

Doculam. What's that? Very Happy

I just finished covering a Lazy Bee I started a couple years ago tonight with some. Now to the most tedious part, and the one I hate most. Installation of electronics and tail surfaces! But not much will be posted here as I had built it for the bad type of engine...

NEW222 Sat Feb 27, 2016 12:02 am

I will keep you updated on things as I go along with it. I will not be able to start till at least next Thursday as I will not have time to get my glue for the project till then. Followed by a weekend of Canadian Power Toboggan Championship Racing.

roddie Sat Feb 27, 2016 10:22 am

I hope you're able to put that foam to use.. especially if you have a lot of it. I agree with Phil, that you need to reinforce a foam-board fuse with something. Two layers is a bit thick for what I'm guessing is a 1/2A model. If your going with a beam-mount.. you could cut slots in the foam for 1/4" square maple beams, and face them with 1/32" ply-doublers. The doublers would also give a radial engine-mount more support with cheek-blocks. Another option is laying-out a single-layer foam-fuse "core" with straight 1/4" square hard-balsa rails; top/bottom the full-length, tapering at the tail, sort of like a vee >.. You can then add foam-contour pieces over the rails.. (nose, belly, canopy, turtle-deck profiles etc.) to match the plans and still retain the 1/4" thickness as if the plan called for 1/4" balsa sheet. This would add some rigidity and keep it light too.

Some considerations for the wing might be 1/4" balsa leading and trailing edges. Maybe 1/4" square rounded-off for the L/E.. and 1/4" T/E stock? Layout your foamboard-wing with this added wood figured into your chord measurement. Maybe cut a square hole for a flush-mount bell-crank block made from 1/4" hard-balsa treated with thin CA to harden it.. (grain running chord-wise) and install a bushing for the screw. Your CG will probably be further back I'm guessing.. when compared to a design using a 1/8" sheet balsa wing. It's hard to say with foam. I guess it would depend on it's density.

Nothing ventured.. nothing gained.. right?

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