You can add braces to the tailplane which will help. I have had a few horizontal stabalizers break in flight on 40 size planes. I used thin nylon cord all the way around on a Thunder Tigre profile Extra that had a problem. It cured the flex and made the plane fly smoother. Before moving the UC (UC= under carriage >> landing gear for the states) forward check the center of gravity. It may be too far forward. Roll the plane inverted and if it takes an excessive amount of down then the CG is too far forward and needs to be moved back.

EXCAP232