I now have one fin with a rib and one without. You can't "squeeze" the fin sides together on one and you can get a liittle concave-result on the other. It springs back immediately and is stiff.

I have full length fuselage braces in both, resulting in very stiff assemblies. I also put the rudder-tray very high in the fuse, in-line with the end of the brace. There is a vertical former that prevents the canopy opening from twisting at the back. Two bolts per wing stiffen the center. I also thickened up the stab tube and siliconed the stab halves to the fuse sides to take out the stab rocking that was there on both of them.

With all of the above, there isn't much left that can be done. It is either going to hold up on not!

Regards,

Eric.

Attached is a pic/sketch of where the fin rib is fitted