For what it's worth.....

Maybe I should expand a bit more on what I have done and why, relating to wing joiners. Everyone has their own experiences that drive their decisions and this is mine...

I had an instance where I probably got a bit too agressive with my trainer a couple of years ago and the wings folded cleanly at the center joint. After looking at how it failed I came to the conclusion that the joiner was a definite weak link and I decided to look for an alternative. After looking at engineered materials and wood, I decided to stick with wood for convenience and fabricated some joiners out of aircraft ply, oak and maple. Wood properties vary with respect to type, variable quality, moisture content and grain, however, maple is the strongest with oak closely behind (per my engineering handbook). I conducted non scientific break tests without measuring moisture content or forces and it was clear that the maple I was using was supereior. Oak is also superior, however it has a much coarser and variable grain when compared to maple. I feel that this coarse grain could also allow many starting points for crack propagation to begin. The ply joiner was weaker and the strength of ply is very dependent upon the quality of the laminating adhesive and the quality of the wood "fillers" in the laminate. There may also be voids inside. So, now I make my own maple joiners for all of the ARF's that I assemble. In my opinion this makes the center joint the strongest part of the wing structure - especially if you add glass. The result may be that some other unknown part of the ARF wing may fail before the center joint, but I have had no other problems to this point. I stress ARF's here because when you build your own kit, you know how well the structure is asembled and you can ensure that it is robust right from the start.

Steve