Fiberglassing a Wing Center Joint - Tips Needed

Harry-

The purpose of fiberglassing the center section is simply to reinforce the joint between the planking on the two wing halves so it doesn't pull apart during high-wingloading maneuvers like tight loops. If there were no dihedral joint and the planking were continuous, there would be no need for fiberglassing.

For a typical .40 to .60 powered plane with 1/16" or 3/32" planking, one layer of 5 oz. cloth should do fine. I'd cut it about 2" wide to overlap each half by 1". The epoxy or polyester resin is only used as an adhesive, and with smaller planes and lighter cloth I often just use regular Titebond wood glue.

-Dave

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The link is an awesome site and it covers just about everything

Steve

On Sun, 12 Mar 2006 23:53:55 -0800, Harry Sanchez wrote in :

That's way overkill, but no harm done--it will work just fine.

Here's where you get to do what YOU feel like doing.

I would make the strip at least as wide as the fuselage, maybe a touch wider. That's overkill, too, but I don't want to do the destructive tests that would establish the real optimum for my wing design and materials.

I'm going to use 6" for grins. Maybe 4" is better. Depends on the size of your plane.

Cut a 6" strip long enough to cover the bottom of the wing.

Put the dry fiberglass in place.

Drip a tiny amount of resin down the centerline of the fiberglass.

Scrape from the center toward the edges with a credit card or epoxy squeegee.

The resin that counts is the stuff that is inside the fiberglass and in contact with the surface below. Anything left on top is wasted weight, so squeegee pretty good if weight is an issue.

Let the fiberglass dry pretty thoroughly. If you have any excess at the leading or trailing edge, you can trim it off with a razor or razor knife when the epoxy is half-set or you can wait and sand it off when it is fully set.

I like to have the top piece overlap the bottom piece about 1/4 to 1/2 inch. It's just an aesthetic judgment. I feel better doing it that way, although there would be no measurable difference in the joint doing it differently.

One.

That means you try to press down the edges and/or leave a little extra epoxy at the edge so that you have less sanding to do to make the edge of the fiberglass disappear smoothly into the surface of the wood. I haven't worried about that much. A lot depends on your own taste.

There are a lot more engineering complications to think about if you like thinking about stuff like that. But if you just want to get the wing together and go fly, almost anything will work just fine. Chances are quite good that something else will break before the wing joint does.

Marty

Martin,

We must have attended the same school of model building : )

I learned from good ole Carl Goldberg...the kits that is.

CJ

Great site, Mosher. Thanks for pointing it out.

Harlan

I like to use lighter weight glass cloth and go out wider than the fuselage as well. This way the fibreglass takes some of the impact/scuffing where the fuselage sits on the wing (or vice versa): I believe there will always be some movement there anyway plus localised loads on landings, though more so with a low-wing models.

Mike