Ok, maybe I'm weird but if I want to circle I just bank in the direction I want, and engage autopilot. It continues the orbit it that direction, at that bank angle. So if you are manually piloting a turn that is circling you perfectly around your target, you should already be good to go once AP is engaged. If you press l-control l-shift h, it shows you if the autopilot is in orbit or level mode. I think orbit is alt- a. Whenever I switch to gunners, autopilot auto engages in level or orbit mode.