This video is of some loiter testing I did this morning of my Trex450 running the latest arducopter code, 2.0.50.
If it were a quad I might not be super happy with the results but for a traditional heli, I think this is a pretty good performance. The altitude hold is very solid using Jason Short's latest code paired with a maxbotix MB1260 XL-EZL0 sonar which is mounted on the tail using a custom 3d printed mount.
There's some more work to do to resolve the circling (which is always in the clockwise direction by the way). I guess what's happening is that the heli is always missing it's target - so for example if the loiter point is straight north, it's actually heading slightly north-west. I suspect the problem is either:
Also the P and I values need some more tuning to stop any overshoot.
This code is the latest and greatest and can be downloaded from the APMissionPlanner. By the way, if you're not familiar with the arducopter code for the heli, it's 95% the same as the quad code, just some changes here and there to deal with moving servos around instead of motors.
If anyone has any other ideas, comments or advice on the circling or anything else, I'd love to hear them.