Mxsmanic wrote:
In simulation, if I set the autopilot to maintain the altitude, and
then try to change pitch with the controls, the control surfaces
barely move, and I can hardly have any effect on pitch.


There's a big difference between airline control movement and it's
relationship to trim than light aircraft. I'll restrict our talk
to light aircraft.

I think this is a limitation of the simulator. My guess is that, in
real life, the autopilot continuously adjusts trim, and so, if you try
to change pitch with the yoke, the A/P retrims to cancel out your
efforts, and the net effect is that you can change pitch, but you must
exert very high control pressures to do it (in order to overcome the
trim that the A/P is applying to neutralize your efforts).

My autopilot has both pitch servos and trim. You push on the yoke
it has the same impact that it would if the autopilot wasn't there.
However, what the autopilot does endeavor to do is adjust the trim
so that it's always "trimmed" which means it may try to trim away
your force (if you are pitching it away from where it thinks it
should be). The autopilot does this so that if you kick off the
autopilot it's giving you a plane that is in trim.