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Jul 18, 2001, 05:58 PM
Registered User

A question for dave-lilley & others as well


Dave
Working with a foam airframe for the first time. I have tried the polycrylic & silkspan
on some test units & am pleased.However I want to add some light glass to some areas and was wondering should the glass go on before the silkspan or the other way around.
I was thinking(gets me in trouble some times)
that the glass would need sanding & that might be hard to do if the silkspan was in place.
Am open to all ideas.
Thanks

Have A Ball

Hans
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Jul 18, 2001, 06:21 PM
Registered User
Hans,
I haven't covered foam with silkspan, but have used fiberglass and polyurethane to cover a foam J3 Cub I designed. Unless you fill the weave you will not get a really smooth surface. I don't care that my Cub is pink so I haven't tried filling and painting yet. If I were you, I would put the glass down first, let it dry and add a second light coat of polycrylic to ensure a good bond. Then you can fill the weave with a lightweight spackle and sand it smooth. Cover that with the silkspan and you should end up with a really smooth surface.
The glass will go on easily, but if you touch it while it's wet it has a bad habit of pulling off of the foam. I used latex gloves and that seemed to fix that problem.
One last thing I should mention. Plain glass and polycrylic adds strength to the foam, but it doesn't add any dent resistance to the foam. My trailing edge is pretty thin (~1/16") and stiff, but if I push at the foam with a fingernail it will dent the foam.
Mark
Jul 18, 2001, 07:31 PM
Registered User
I've never glassed a plane and I can only regurgitate what I've read on the subject.

However, I can offer some advice with the poly and silk. When I wanted to add more strength with silk and poly, I just added more coats. The combo is so light that even adding a couple doesn't seem to add all that much weight. If you want even more strength, I've heard that you can use light-weight brown paper instead of Silkspan. It doesn't form to compound curves as well so you may have to make cuts to keep it from creasing. According to those who have done it, the result is very strong even though it weights bit more. I haven't use brown paper yet, but I have used brown paper tape. I used it to protect the LE, wing tips, and the joint between two wing halves. It worked VERY well and it is light weight too. Before you put it on, I recommend that you spray on a light coat of 3M-77 to help it stick better. Then, you cover it with the silk and poly. Be forewarned that if you do not sand down the tape edge, it will shop when you paint your plane.

I recommend try this method too to the areas where you need more strength and/or protection.
Jul 19, 2001, 02:27 AM
Model Designer
keven64's Avatar
Dave,

The brown paper tape.
I have rolls and rolls of the stuff !
I never thought of using it as you describe !
That I have has reinforcement of diagonal weave within it - is the same as that you use ?

Keven.
Jul 19, 2001, 05:36 PM
Registered User
dave
I was just going to add some 1/2oz. glass to the nose & belly for skid protection-- no landing gear!
I plan to layer two coats poly,one silkspan,one coat poly,let dry, sand,one more layer silkspan,one more coat poly,
sand
and then paint with airbrush.
Do you think the glass would be too much?
Thanks

Have A Ball

Hans
Jul 19, 2001, 06:38 PM
Registered User
The brown paper tape that I'm using doesn't have threads, but the threaded kind would probably work too.

VaVol,

I thought about putting something extra on my 'Lil Sporty to protect the bottom, but after the tape, the two coats of ploy and silk, and the spray enamel paint, I think that anything more would have been overkill.
Aug 01, 2001, 09:19 PM
Registered User
dottney's Avatar
Please excuse my ignorance but what is this polycrylic stuff? (brand names will be appreciated)
I thought polyurethane would melt foam.

Thanks
Dave
Aug 01, 2001, 09:46 PM
Registered User
Dave,
Polycrylic-water based polyurethane by MINWAX-SAFE FOR FOAM.
Aug 02, 2001, 01:35 PM
Gravitationaly Challenged
jmelzer's Avatar
I have had success using thin Balsa sheeting (1/32" - 1/16") over pink foam to strengthen leading edges and fuz bottoms. Apply diluted Elmers carpenters glue to both surfaces and allow to dry. Place the wood on the foam. Heat with an iron set to high to bond. Sand to suit your taste and further lighten. THEN cover with Silkspan and polycrylic, I use the Minwax brand.

Now I have a question... I apply the Silkpan and spritz it with water to smooth it out on the surface, but I still get some little wrinkles. Is there any way to obtain a smooth aplication right from the start? Or is sanding the only way to smooth these?
Regards, Jay
Aug 02, 2001, 01:49 PM
Registered User
-- Materials:
“Spackle” is sold by under various brand names including Red Devil and Bondex as “Lightweight Spackling Paste.”
“Polycrylic” is a superior polyurethane like product that is sold by Minwax as “Ultra Fast Drying Polycrylic - Protective Finish.”
Both of these products clean up with water and both can be found in most hardware stores and the hardware departments of most large discount stores.