The best-tumbling plane I've ever seen is the Seagull Extra 40 ([link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXGPL7&P=ML]this one[/link]). That plane would tumble instead of snap. Small control surfaces but an effective rudder and thin wings will give you snaps, and the heavy wingloading lead to good tumbles. A guy that had been flying for right around 6 months, this was his third plane, and he was doing tumbles 30ft above the ground at full-throttle parallel to the ground after 10 flights. He told me to try it, and it was as simple as doing a snap roll. He had an OS 46AX in it and standard servos. I know tumbles are CG-dependent, but I have no idea what the GG was....sorry.