Spaceclam

I have a large foam disk, 2" thick and i may need to cut out a lot of it for weight purposes. it is 1 lb/cu ft polystyrene foam and i need suggestions on what material may be useful if i were to cut out big chunks and wanted to simply put a thin cover over it to save weight. the material needs to be able to in some way conform to a shallow dynamic curve, it needs to be at least as strong as the foam it is replacing, it needs to look solid from the top and look the same underneath paint as the foam right next to it. i am thinking either light fiberglass and not putting resin in the part that is not adhering to anything, or maybe monokote or someting. any suggestions?

Mike James

See Peter Thannhauser's excellent article on this, here on RCU, at http://www.rcuniverse.com/forum/m_25.../tm.htm#256678

Spaceclam

that would work nicely, but i dont have the tools to do it i dont have any hotwire systems or aluminum jigs, nor the lathe to make them. i may be able to dremel it out, but it would be a better option to simply cut the foam out completely where i do not need it and cover it with something lighter than the original foam.

Mike James

Well, the way Pattern guys have done it for years is to remove the foam, then sheet the entire wing with lightweight 1/16" balsa. (I note that you said a "foam disk", rather than a wing.) If you want to keep it light, use a film covering, otherwise, it could be glassed. But glassing defeats the purpose of removing the foam.

Ed Smith

Before you do anything check the weight of the disc you have. Calculate the weight saving by removing what you intend to remove. Calculate the added weight to fill the hole.

You may find that the weight saved is so small as to be not worth the effort. I have done this in the past and I saved virtually nothing.

Ed S

Spaceclam

the disk (yes, i did say disk) is 12 oz. i am using expanded polystyrene foam at 1 lb/cubic foot. the whole dohickey weighs 12 oz. my trouble with balsa is that it doesnt conform too well for a slight dome shape. it will conform along the grain, but not against. does covering film stick to styrofoam?

iskandar taib

My Feedback: (5)

Yep.. Low heat iron-on works. Solarfilm and the like.

You can also use packing tape. This comes in colors if you look around (do a web search on "zagi" and "tape"). Iron it down and it'll stick permanently. I personally cover bare foam with USI Opti-clear (a laminating film).

mccoy40

My Feedback: (6)

The control line combat guys use silkspan and thinned white glue. When wet, the silkspan will conform to any shape and will shrink as it dries leaving a very strong thin skin. More strength needed? - add a second sheet of silkspan in a different direction similiar to plywood. Silkspan should be dampened with a wash cloth before applying. The glue should be thinned two parts glue to one part water. Apply a coat of poly urethane to it after it's dry and then it will be fuel proof.