Not flying straight with Autopilot (AFC and ALT HOLD) enabled

[brunodk]

With AFC and ALT HOLD enabled the AV-8B can't seem to fly straight all the time. It slowly turns in either direction, sometimes more, sometimes less.

If the load is asymmetrical the turn is quite significant.

 

How I've tested:

• Create mission with AV-8B in flight with one waypoint and GPU-12 on the outmost stations.
• Start the mission and trim the aircraft straight for the waypoint. Enable AFC and ALT HOLD. As the aircraft comes closer the waypoint slowly comes off-center. E.g. the airplane is turning.
• Replay the mission. Jettison one station and trim the the aircraft for the waypoint. Enable AFC and ALT HOLD. The aircraft comes off the waypoint quite quickly.