I'm building up a pair of Piedmont Temptations from their basic kit (what a deal!). Hopefully the pics and descriptions of what I can offer will be of some use. Starting out a bit in the middle though, mainly because I wanted to get some pictures out of a method of securing the wing tube socket end as a followup to a post on the NSRCA list tonight.

I build up a snug fitting plywood and balsa box that fills the tube socket cutout in the foam core. This is done for two reasons. The most important reason is that it roughly triples the gluing surface area as opposed to the usual method of securing the socket with a single ply plate. This will greatly delay the onset of fatigue damage to the interior of the core. What frequently happens is that the foam beads along the glue joint to the ply plate will crumble and eventually allow the plate to completely separate inside. The tube socket then is floating around and starts to work at high stress against the balsa skin. Failure of the wing panel is imminent and you are lucky if you notice the impending failure in time to repair it.

The second reason for doing this is more of a freebie benefit, but there are sound structural reasons for it. What you get for free is that there is now support for the balsa skin over what would normally be an open hole in the area of highest stress on the skin. However unlikely it may seem, the skin that is in compression during high G maneuvers is always trying to buckle in against the foam core. When there is nothing but a hole underneath, it makes it more likely that a compression failure can occur. This little tube socket box elimiates the hole (obviously!) and adds a bit more structural integrity. Basically, this entire process eliminates a high stress point in a location of the wing where it can normally do the most damage.