Striderjg: What size engine you you have on your PT-40? I'm in the process of completing a PT-40 with a OS .50SX, and from what I can tell - it'll be tail heavy too. I may have to put the battery behind the F3 former, but don't know how to secure it there, as there's a lot of space between F3 and F4. Any suggestions? if all else fails, I probably make some sort of a tail skid with the right amount of lead weight in it and epoxy it the the bottom tail section.