I will make a guess or two. If its a 60 size plane (you didn't say). I would think that the 11x7 is too small. I would try about a 14x7 or maybe 13x8. I don't have the specs on the plane but its a 40 size with a 60 class engine it may be nose heavy. Either way the ruff CG should be about 1/3 of the way back from the leading edge of the wing. About where the wing is the thickest. If you do need more weight to the rear you can allways move the battery back further instaed of adding other weight. Good luck, mxerman