Hi!
I nearly crasched my Viper this summer due to a weak tail that broke in half. I had lots of up trim 3-4mm and decided to saw away the stab using a japanese razor saw and relocated the stab 3mm down at the leading edge. That removed any up trim problems so now I have just a 0,5-1mm up trim.
I don't have any trim problems what so ever when flying my Viper.
It flies straight as an arrow at full speed and just loses hight when I reduce throttle, just like a normal racer (airplane).
Nelson LS engine is set at 0, Wing at 0 and stab relocated 3mm down at the leading edge.