I have been using an APM 2.5 in an actual aircraft connected to my laptop running Mission Planner just for recording pitch/roll/yaw and comparing it to the "gold standard" G1000 logged data while doing a few roll and pitch step control tests. When I expect a 30 degree roll angle that is held for several seconds as seen on the G1000 data, I get the initial roll angle (sometimes a lot less though) on the recorded MP data but then it drifts back towards zero over five seconds or so. Similar results for pitch. The rates and accelerations look reasonable (hard to really tell - unless the maneuver is dramatic).
I realize that this actual aircraft environment - especially the 100+ knots - is not what has been expected or tested for Ardupilot use, but I wondered if anyone has any ideas to try to improve the APM results. I see that I should probably upgrade the firmware to 2.6.8 since the accel noise reduction has been improved. Maybe this environment is a little too extreme. It's possible that I need to move the APM closer to the CG - I am unsure just how far away it is right now - it seems to be near the quarter chord position and is centered left to right. Also, should I isolate the APM with more foam? I don't feel much vibration and I have two layers of velcro between the airframe and the APM. Any ideas would be appreciated.