Hi Guys,
This has been hashed and re-hasned many times over the years as far as an AP flying the plane with a trim tab. To be quite blunt, it has never worked in an application like an RV as an AP that can move the controls. The AP will always be behind the movement of the actual flight control itself, so on and so forth. No big deal in a 172 that is relatively slow, and relatively insensitive in pitch. The DC9 isn't even worth comparing, the entire flight control system couldn't be any further away than that of an RV (while the elevators in a DC9 may be controlled by servo/anti-servo tabs, the trim is NOT - it's a jackscrew that moves the entire horiz stab - and when that breaks...well, we know what happened there).
There are 2 well proven autopilots out there for RV's that are very reasonably priced (TruTrak and Trio) as well as BMA with their own. Dynon will be selling theirs sooner or later, but at the moment we don't know much about it - other than what little anecdotal responses you occasionally see on the forums from them or some of their beta testers. TruTrak and Trio both have nice optional little boxes that will automatically trim the plane (hooks right into your electric trim system) for you as fuel is burned, or for climb/descent, etc.. and they work marvelously. Of course you need a trim sensing servo to do such a thing.
Anyway, neat stuff all the way around. Once you fly with an AP, you'll never want to go back...no matter which one you choose! Heck, even the NavAid's were pretty darned good in their day!
Cheers,
Stein
BTW - interesting factoid. As of OSH this year, TruTrak has shipped more than 10,000 servos! Can you believe that?!?!