I suspect something about the setup of your plane may not be right, but since I haven't flown that particular kit, can't say for sure.

This weekend, I went out with a Great Planes "Venus .40" ARF, assembled by the book, using only S3004 servos, and did knife edge loops... Never had to use full rudder. (with an OS .46FX and 11-7 APC prop)

I reviewed the "Venus .40" kit on my web site at http://www.nextcraft.com/gp_venus40arf01.html Very impressive for the price.

Good luck!