Newbie76
From the picture in your second post, it looks like your wing may have excessive positive incidence. The only way that I have to measure it is to hold a ruler up to the CRT screen and look at the angle of the wing compared to the angle of the fuselage and horizontal stabilizer. I am not exactly sure what you mean when you say “it goes nose over and is impossible to recover”. But with excessive positive incidence the model may climb out nicely at low speed and as speed builds take more and more positive angle of attack until it stalls and comes right back down. If the model is not in a stalled condition when it impacts the ground then it may be something like the control surfaces twisting/warping under normal flight loads. I do not think that it is a C/G problem. If it balances at the spar then you are approximately at the 25% point. Plus, If it was a C/G problem you would know it immediately at the time of launch. I would check the wing incidence and set for zero or no more than a positive one or two degrees. If that does not solve the problem, then launch and immediately throttle back and nurse it up to a safe test altitude. Slowly advance the throttle and observe the results. If it starts to pitch down immediately pull back on the throttle to recover then look for excessive down thrust of the engine or the horizontal stabilizer bending under load.

Let us know what you find.