ORIGINAL: MIXMASTER
Sounds like you got the vertical tri stock where it should be and the right idea for the blocks too. I doubt the t-nuts will come out without the hardwood block attached,I know this from experience(happened to both planes,I just glued that back on since the break was clean.
I didn't mean that the tee nuts would fall out. I just thought with the block glued in between the formers that you would not be able to get in there in the case of failure. I did tri stock vertically in the four corners, added just one extra dowel between the two stock ones and found that now, on ocassion, I end up poppping the threaded sleeve from the washer on the tee nuts. It seems that with being a minimal re-enforcement, its now stronger than the hardware, or else I need stronger tee nuts. I've been recycling parts from past UCD's.
I think that flutter issues were from those who used 2/56 rods, sub par connectors and weak servos. Flutter has never been an issue to date and the YS 110 would have found a weak link by now. Joe