Crash without any error, Undesired high Roll

Hi, I flew in FBWA mode. The flight was good at the beginning. Everything work good. Suddenly my plane desired roll changed to high values. It exceed the my bank angle which is 45 degree. Then it crashed. I looked logs many times. There was no error or anything anormal. The drive link where the telemetry and dataflash logs are in is Logs - Google Drive.

Perhaps an aileron servo failed?

I checked all servos after the flight, they worked normal. After plane rotated roll, I rotated it reverse from RC transmitter and it responsed that as seens from logs. So I think the problem is result from fully by autopilot.

Unfortunately you kept switching back and forth between FBWA and Auto tune, so I don’t think you made any significant improvements in the tune. I suggest you verify your C of G, and try the auto tune again. Once you’re in auto tune mode, stay there until the job is done. The plane flies the same in FBWA as it does Auto tune, so there’s no reason to switch back and forth.

The plane appears to have stalled at least three times I saw in the logs.

Each time you can see the slow airspeed. Stall speeds increase with bank angle so the high pitch demand with high bank angle is prime for stall. The last stall didn’t have a demanded bank angle, but the stall is clear and the airspeed is very low. On a tuned airplane FBWA is really good at keeping you out of a stall, but it’s not good at getting you out of one once it’s happened. No flight controller in the world can overcome the physics.

My suggestions:

Thank you Allister. Now I see the problem clearly. The airspeed is very low and autotune procedure is not good performed. Another fact that the weather was very bad, strong wind was exist. I knew that the this weather was not suitable for autotune. I just wanted to see the limits :slight_smile: . I will try your suggestions. Thanks again.

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