Thanks to a question from my buddy Mike, I've confirmed that the autopilot parameters in the .air file affect the behavior of AI aircraft.

Originally, when adding a couple of Stearmans and a couple of Twin Beeches to the AI traffic, the aircraft couldn't get lined up with the runway at their destination, so couldn't land, resulting in a series of go-arounds, then winking out. So I took the default C-172 .air file, used AirEd to tell it that it was a taildragger, and made a separate AI entry in the aircraft.cfg file, with the only difference from the version that I fly being in which .air file is used. This worked well, so I did the same thing for the Twin Beech using the .air file for the Baron. It, too, worked well. But it resulted in performance for the Stearman like a 172 -- OK for AI, but not the best. Same deal for the Twin Beech -- it performed like a Baron.

So, after Mike's question about whether autopilot parameters may be part of the answer, I used AirEd to compare the Steaman_AI with the Stearman .air files. While many parameters matched, there were several which did not. So I changed a dozen or so parameters in the PT17 file to match the Stearman_AI (172), and repointed the aircraft.cfg file for the AI Stearman to the modified Stearman file, then followed the Stearman from Jeffco to Centennial.

It taxied fine, cruised more slowly (more like a Stearman -- about 95 kts) and made a successful approach and landing on Centennial 35R. The only thing wrong was that it touched down just short of the runway and came to a stop on the numbers. ATC told him to contact ground, and he taxied in to parking.

I tried the same thing with the D-18, only I changed every difference between the Baron (AI) .air and the d-18 .air. The aircraft took off fine, and got into the Centennial pattern, but on downwind it descended to the ground (out of my sight) and tower told him to contact ground. I never saw him again.

So in both cases there were decided behavioral changes from modifying the autopilot parameters, but it is yet to be determined which parameters have the most effect and which one can be left alone. Also, some of the changes I made on the Twin Beech made it worse with the non-AI (original) .air file than before the changes, so evidently you have to be selective what you change. Certainly the C-172 and Baron parameters didn't match each other.

Larry N.