Originally Posted by
acerc
I don't think the cabane mount is a stress issue but rather a bolt issue. The wing to cabane is a 4-40 through the wing mount and a tube through the cabane. The wing mount is held by two 6-32 bolt's into the wing with blind nuts on the back side. If I were taking a guess I would say those two 6-32's have backed out a turn. These type's of issues are also why I said when I return from the trip I was going to disassemble the plane, correct known issues, check for the unknown, and make the changes mentioned in previous post.
If it turns out that you are correct about the 6-32's backing out, I have ONE warning (from experience - where else!?! LOL) DO NOT PUT ANY KIND OF BOLTS ON TOP OF THE BLIND NUTS! That can (probably will) cause the bolts to break and the top wing to depart the aircraft. Under those conditions you have to be very lucky and very good to recover the aircraft and repair it. Lucky in that it has to happen at the right place and you have a landing place readily available and very good because you have to have the faith to bury the nose and throttle to keep the flying speed way up because when it stops flying the party is all over. This makes flaring a real trick!
It turns out what happens is that as you do various maneuvers, the top wing shifts but that shift is hidden and is only seen as load on the structure. By adding bolts on top of the T nuts, you will have taken the 'slack' out of that part of the structure that flexes so the movement is applied totally to the bolt. The struts just are not enough to hold that top wing on even if this happens to occur at the top of an Immelman, which is where my Super Stinker came apart. That was one hell of a landing! The hardest part was NOT watching the top wing flip its way to the ground.
In short, add lock washers to the bolts AND use Locktite and put those on your preflight list.