RE: Differential
Without differential, when you rollup to turn at #1 the right airloin (which is deflected down) has more drag than the left airloin (which is deflected up) and causes the plan to yaw toward the right wing, which pitches the plane up when you are rolled at 90* getting ready to pull around #1. Then you are out of wack when heading back to @2. The difference is subtle, but i could see the difference when i put the differential in.