Foam for wing tips under UltraKote?

[Dennis Toth]

Guys,
Working on a new project and I need to have shaped wing tips (to add area). I though of doing the balsa block route but this is a test ship and light blocks would be a waste. I was wondering it anyone has used foam (blue, pink, green) for a part that was then covered direct with UltraKote? I know guys have used the foam and fiberglass and this is possible but covering direct would be simpler for this ship.

Thanks,      DennisT

[Tim Wescott]

Styrofoam will melt under Ultracoat.  If you were willing to compromise on the covering and use something low heat, styrofoam would work great.  Most beaded styrofoam is white, but the continuous extruded stuff comes in other colors -- but it'll still respond to heat and solvents the same way.

Polyurethane foam (the green stuff that sells to dry flower arrangers in craft shops) would, I think, stand up to the heat, but it's pretty crumbly -- I'd want to slap on a layer or two of light fiberglass if I used it.  I've seen it sold as "plastic balsa".

[Avaiojet]

Den,

Why don't you just add a rib or two on each wing tip and have flat wing ends. Not stylish but it's a test ship.

Besides, I still have your heat iron. 

[Dan McEntee]

   Carve, sand and shape your foam tips. Then apply layers of silk span with white glue, getting it as smooth as you can. Lightly sand between coats of glue/layers of silk span. Blend it in to your wing. You may be able to adhere the covering this way, or at least you can now paint the tips. Just let everything dry thoroughly. Another thought is to shape the tips, cut them loose, then lay up epoxy and fiberglass on the tips to get the shape, then dig out the foam from inside the glass. You can make cowlings this way also. The original "Lost Foam Method!"
   Type at you later,
    Dan McEntee

[phil c]

It's been some time, but I've covered bare white beadboard foam with Ultracote.  It was pretty sticky all by itself but ironed down OK.  Just don't let the iron rest in one spot.  Doing the tips, apply the heat past where the covering contacts the tip.  The covering will soften and you can pull it down over the foam.  Dan's suggestion of a layer or two of silkspan over the foam is a good one.  Actually, any soft paper will do., silkspan just has better wet strength than most.  You can also apply a fairly thick(1/32in) layer of lightweight spachltling compound(Red Devil, DAP, etc).  Sand it to shape and cover.  It makes a pretty good insulator too so you have more leeway in applying heat.

Phil C