I am trying to tune the ArduPilot for Bevrc X-5 plane. At the moment I am playing with roll P gain and trying to achieve acceptable stability in FBW mode. Also, I am trying to overcome the plane peculiarities: he has tendency to roll in positive direction (left wing down) and because of this, rates of left and right turns are not equal.


In order to get an idea what is going on during FBW flights, I converted flight logs into charts which display desired (navigation) roll, and actual roll detected by IMU.

I started from P = 0.003. It seemed to be too much for my plane, because oscillation amplitude is pretty high. The plane even was unable to turn right due to the oscillation. Attached LOG00220 demonstrates how it looked.  

Then I tried to reduce P gain down to 0.002. This gain value worked much better, oscillation reduced significantly,  but sometimes the plane could not keep navigation roll during left turn and tried to fall  into left spiral. LOG00221 shows this test.

Then I reduced P gain to 0.001 (LOG00222). The tendency to fall into left spiral becomes even more visible, although oscillation almost disappeared.

Now I am going to stay with P=0.001, and will try increase I gain in order to achieve better stability. I appreciate any hint how to tune P and I gains correctly.

LOG00220-20120601.html

LOG00221-20120601.html

LOG00222-20120605.html