The Advanced Flight Model 2 isn't bad, there are only a couple of items that are not physics based. FM2 uses an artificial vertical restorative force rather than off-setting the center of gravity of the helo to use the weight to correctly bring it back to vertical. There is also an artificial heading restorative force which they used instead of modeling the rear vertical stabilizers. Everything else is correctly physics modeled, especially the main rotor. The body drag force should also be moved slightly if I move the center of gravity and the weight force. Other than that, it's actually a pretty good model.
The "G" key Auto-Pilot is another issue altogether, it's not physics based at all. It moves you around without any basis in physics. I'll look at that next, maybe in a few weeks when I get back from the next work trip. Enemy aircraft are probably controlled the same way, but you don't notice it as much since you aren't in the cockpit.
Thinking about it, there are two other forces/behaviors that could be added in. When you hover the helo will drift sideways because of the tail rotor side force. You need a little cyclic angle to counter it. In most helos the manufacturer off-sets the weight distribution to remove this tendency. There is also a gyroscopic force that could be modeled. Let me see if I can get this right... While you are in the act of turning to the right in a helo with a counter-clockwise main rotor, the nose will pitch slightly down during the turn. Turn left and it pitches up. That might be backwards, I'd have to get out my dynamics text to check. These behaviors are hardly noticable, so it isn't that big of a deal if they aren't in the sim. I can go through the code and put in the weight restorative force and the rear stabilizers and remove the artificial ones if you guys want me to. It's pretty close to accurate now, though.