Structural Repair

[Rcmaster199 at aol.com]

In a message dated 10/14/2002 6:51:15 PM Eastern Daylight Time, 
DGundling at compuserve.com writes:

> Subj: Structural Repair 
>  Date: 10/14/2002 6:51:15 PM Eastern Daylight Time
>  From: <A HREF="mailto:DGundling at compuserve.com">DGundling at compuserve.com</A>
>  Reply-to: <A HREF="mailto:discussion at nsrca.org">discussion at nsrca.org</A>
>  To: <A HREF="mailto:discussion at nsrca.org">discussion at nsrca.org</A>
>  Sent from the Internet 
> 
> 
> 
> Had a wierd one while flying Saturday. The wing on my Legacy Lite went from
> slight dihedral to noticeable anhedral in flight. Was able to land the
> plane OK. On checking I found out the wing had failed right at the center
> of the two wing halves in the middle of the fuselage. Would have expected a
> wing failure to occur just outboard of the center section fiberglassing.
> The failure was almost like a knife cut at the wing joint. The fiberglass
> and wood on either side of the break were pretty much OK. The fiberglass
> was stuck to the wood and the wood was stuck to the cores (wood put on with
> epoxy). Question, what is the best way to repair the wing. Put new
> fiberglass and epoxy over the old or take the old fiberglass off and stick
> the new glass to the wood. I am leary of this as I am liable to tear the
> balsa wood off while trying to get the old fiberglass off. Will brace the
> joint with carbon fiber this time. How far out should I run the new center
> joint?
> 
> Any ideas on a better way of doing it appreciated.
> 
> Dave

Dave,

It sounds like too much sanding at the wing center  joint. It also sounds 
like whatever glass you used, would have been plenty strong, since the wing 
did not really fold completely. Apparently there was enough strength left, 
perhaps from the bolts, since you landed the plane. 

To repair, roughen up the glass in the center section with 60 grit paper and 
lay another piece of 6 oz/yd  minimum over that. You just have be certain 
that the glass is roughened very well so the fresh epoxy has bite. I would 
not try removing the old glass since  too much of the wood may be removed.

For one piece wings, my procedure is to first make sure the skins from the 
two panels mate properly with minimal gap, and then glue these together with 
Pro-Bond and water.  I let this cook off overnight, and then come back, touch 
up the foamed Pro-Bond  at the joint a little, and then lay a 1" piece of 4 
oz cloth all around the center. Then I lay another piece of similar cloth, 
about 5" wide, over the first. The first piece is a little insurance in case 
I get a little heavy handed with the sandpaper on the second, wider piece. I 
have never had a wing center section fail (or stab, except, 2 oz is plenty on 
stabs)

Matt K
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