Yeah, so that would cause the problem. Mine is a touch tail heavy halanced on the main spar, it flies very well, although I think that my 8 year old son will take over the plane this season as I am now on to my first low wing (4* 60, and have a Twinstar, Corsair and Cub ready to go, not to mention a 1/4 Chipmunk that just needs the electronics put in be ready) The PT-40 is a great little trainer, I hope you built the B wing, the A has way too much dihedral in it.

Good luck and please post a picture, would love to see how yours turned out.