Hi Gang,

I'm building a Wendell Hostetler 29% Gee Bee Zee from plans, and he's calling for urethane foam for the wing fillets, then covering them in 1/16th balsa. I've not used foam of any type before, (the Zee has very large fillets) and would like to know what's best to use, along with how to best shape and attatch the stuff.

Thanks for your help!

Jim

Urethane foam is the stuff they use for insulation in the spray cans. It expands after it is sprayed. Shape with a razor, and sand. You might get better answers posting this in the scale forum. Good luck.

With large fillets, I would use balsa blocks. I would be concerned that the foam would be easily damaged just from handling the plane even with 1/16 sheeting over it.

That spray can foam is really pretty tough stuff, but it continues to expand for a considerable time. I filled the insides of a vacuum formed pilot bust with it, and a month later it was starting to come apart at the seams.

Les

Thanks for your help guys! I found out about a product called Superfil from Stits. It's light, doesn't shrink, and sands easy so they say.

Jim

I have used styrene foam for fillets in smaller planes with no problems. I usually just fiberglass over it and it has been fine. Covering in balsa and then fiberglassing will most likely insure you from any reasonable handling damage.

Wonder if he's referring to this stuff...
http://www3.towerhobbies.com/cgi-bin...?&I=LXBH62&P=0

Would think a large dowel wrapped in sandpaper would help shape it well, though I've yet to use this stuff.

Jim,

I used green "floral" foam from the craft shop to shape fillets for my Pitts Super Stinker. It is very easy to work with, just harden the material with thin CA and kicker. I follow-up with a thinned mixture of epoxy and milled fiberglass. Sand the high spots then fill as usual.

The floral foam (green) or the pink or blue sheet foam (Home Depot, Lowes) will work quite well. It is easy to cut and sands well.

I agree about the 1/16" balsa sheeting and the possible lack of protection for the foam. I suggest 1/32" ply to sheet the filets with. If the filets get damaged with the ply on them, the filets are going to be the least of your problems.

This is my first time using green foam to shape fillets. It was amazingly easy to shape but very delicate until treated with thin CA. Just allow the thin CA to soak in and LIGHTLY spray it with kicker. This stuff will handle the CA, kicker, and chemical "heat" without any problems. Just make sure you like the shape BEFORE using the CA. It gets rock hard and requires aggressive sanding after treatment.

I don't believe covering with balsa is needed for extra strength. However, it's cheap enough to try for yourself, just a couple of bucks at the local craft store and test it before using it on the plane.

I'll post more pictures later today.

Foam fillet after filling the low spots and blending.

Have you ever tried Leather Fillets? Old control line stunt model makers trick.

Bill Sawyer sells them and he can be found on the Stuka Stunt Works forum. They come in many different sizes (widths) and they CA in place. You just buy them buy the foot. They're like belt leather only they've been cut to fit in a corner.

They work EXCELLENT and you can paint them.

That's a new one on me... and I've been around for a while.

Superfil is the very best, Easy to shape and easy to sand.

You can smooth it out befor it completly sets with a wet finger.


Regards

Here is a cowl modification using the green foam method.

Texan, thanks for the insight i have been working on a waco making fiberglass parts is a trick
to learn. I just made a tool box door with working latch, my question is when you fiberglass
over the green foam does the fiberglass eat up the foam?

Roger,

I am very pleased to say that green floral foam is not eaten by regular thin (ZAP) CA, kicker, or epoxy. It has proven to be very easy to work with.