Interesting comment about jets, Rick. I’ve only flown a jet once (Albatros L-39) and the one thing that really stood out was the pitch sensitivity - I found holding level flight much harder than in a slower plane.
And as for the rest of it, I think you’ve summed it up well - the harder you try, the harder it gets. Like crosswind landings - while you’re trying to think about what you’re doing, it just gets harder, once you get to the point where you can relax and let your subconscious take over, it all just happens. It’s great watching really good, smooth pilots - they appear to be paying absolutely no attention to flying the plane, yet it goes exactly where they want it.
Clark, I don’t disagree with what you said, but would note that the Cirrus is somewhat different to the typical light aircraft, and probably different to the referenced accident planes, in that the trim and autopilot servos are the same thing, whereas the typical a/p setup has dedicated servos (with an override clutch that offers quite a high resistance) plus in some aircraft the a/p can drive the trim servos, to relieve loads on the a/p servos. The failure scenario is that the autopilot servo drives too far one way, but the a/p runs the trim the other way to compensate, when the pilot finally sees a problem, and disconnects the autopilot, he suddenly has major out of trim forces to overcome. The SR20 setup is quite different and this scenario basically can’t occur (not sure about the SR22, I seem to recall it has a separate a/p elevator servo). In both, though, the maximum out-of-trim force that would have to be overcome in a runaway trim situation is quite low, as it’s just spring pressure, not aerodynamic force from a trim tab. fWith some other planes, overcoming full elevator trim can be very difficult. Also, with the SR2x, if the trim is moving, you see the stick moving. I’d also note that the MU-2 that you mention does have manual (as well as electric) trim.
In summary, I think the SR2x setup eliminates several failure possibilities, without introducing any new ones, and the lack of a manual trim is not a significant disadvantage. The major drawback in my view is that the stick loads are still quite high at low airspeeds (because the springs don’t know you’re going slow) - e.g. holding aileron into wind while taxiing is quite tiring, whereas with e.g. a Cessna there is essentially no effort required.
I almost always have my hand on the stick with autopilot. I wonder if the stick movement in a runaway trim situation would be apparent? Or in a stuck left-indicating turn coordinator?
Thank you for the clear explanation of the Cirrus AP. I think that every problem I’m aware of with trim in other planes is due to the situation you described so well… two separate servos working against one another. I had also not considered that a mechanical trim tab in a bad position would require much more control force to overcome than a Cirrus would. It all makes sense now and I can see the wisdom of this design decision. Thanks Clyde, Clark Jernigan
Could the determining factor in the trim rate be the ability of the autopilot to control the aircraft at the minimum autopilot speed? I don’t know why that would be so different in your Bonanza, but given that the roll trim IS the autopilot trim there may be a relation there. In the SR22 the autopilot has a separate pitch trim, so the main trim can be (and seems to be) tuned for pilot comfort.
-Curt