RE: the rational of trimming
Contrary to what has been said above, I have often trimmed out my big bipes to fly hands off in level flight whether upright or inverted at one throttle position (usually about half or two/thirds throttle). Now, if I change throttle position, trim will slightly change. I have also trimmed out several monoplanes (.40 and .60 size) to do the same thing. It is difficult sometimes, you have to play with both the CG position and usually have a little bit of up trim in both ailerons when the aileron stick is centered, especially on the monoplanes.