I downloaded an excellent 2-page "trimming chart" a few weeks ago and have been trying to apply what it says not only to my actual RC aircraft but to an aircraft in my FS One simulator. So far the simulator is responding to CG changes as expected but my airplanes are not. Here's the situation.

The chart says one of the ways to check CG is to roll inverted and see if the pitch increases or decreases. It says if down elevator is required to hold level flight, move the CG aft.

This has worked perfectly on the simulator and on a 33% Edge 540 that used to drop like a stone when rolled inverted, it now flies hands off level flight either rightside up or upside down. Cool.

One of the airplanes I've been trying this out on is an old CG Staudacher S-300 GS. It too drops like a stone when rolled inverted and when I really checked the CG I found that it was actually about 1/2" too far fwd according to the plans. I moved the battery rearward, checked the CG again and found that it was now balancing right at the aft point of the plan's CG range. I cautiously flew it this way and found two things. While it still stalled straight ahead with no real wing dropping tendancy, it still required a fair amount of down elevator to hold level inverted flight. The weird discovery was that when pitched upwards sharply it would start to porpoise up and down. The less elevator I used the less the up and down movement. Switching to low rate on the elevator made it easier to fly but it was a trait I'd never seen before.

Overall the airplane flies better, does perfect single snap rolls, spins upright and inverted coming out the instant you release the sticks, and lands easily as long as the speed doesn't get too slow.

So I'm wondering, if I've seen the result of a more rearward CG having the result shown on the trim chart when tried on the simulator model, why didn't I see it on a real one? Could it be the CG range on the plans is on the conservative side and I need to keep experimenting with moving it farther aft? This is more difficult because of course if I go to far, well I saw on the simulator what happens. And it would be expensive.

What about the up and down pitching when pulling up elevator that wasn't there with a fwd CG?

Is it possible to make any aerobatic airplane with a symmetrical airfoil, that is built straight, with proper wing and tail incidence, to fly hands off inverted or am I chasing shadows or just over simplifying things?

Inquiring minds want to know.

Kurt