Our plane crashed a few seconds after take off. We hand launched the plane in AUTO mode. It took off without any problem and started to mission. After passing WP2, it suddenly incresed the throttle to %100 and went straight to the ground with a roll of nearly 50 degrees. I tried to analyze log files but couldn’t find anything interesting as I am not an expert about it.
We autotuned the plane and it was really nice to fly it with FBWA and Manual modes. We also calibrated the airspeed sensor in our previous flights. We made a few Auto mode flights before that one and all went without any problem and the plane landed safely.
Can anyone please explain me what happened here? I really need help about the issue.
I am deeply unqualified to analyze your logs, as a beginner with ardupilot myself. However, I am trying to teach myself and was curious - if anyone with more experience chimes in you should listen to that person. However, this looks to me like an accelerated stall of some kind. Roll goes to 60, your vehicle is commanding pitch up, and throttle is high, but actual pitch is downward.
During the final period your airspeed is still only 17-18 m/s, which seems like a slow airspeed for a really steep bank of ~60 degrees. What is your vehicle stall speed in level flight? Is there a possibility of a miscalibrated airspeed sensor - your airspeed during the first portion of the flight up to 1:45 (while in FBWA) seems implausibly low.
Thanks for your reply. The plane started to fly aproximtly at 1:47. It wasnt flying on FBWA mode. When it crashed on the ground the air speed graph shows nearly 27m/s. So I think airspeed sensor readings are ok. Stall speed in level flight is 8-9 m/s.
It’s worth stating that flight modes like FBWA and Auto do a good job of keeping a plane from stalling. However, if the plane does stall FBWA and Auto will actually accelerate the stall and make it worse. They will not correct for a stall.
The flight controller was demanding pitch control and sending the output to the servo, but the plane stopped reacting. Possible causes:
Servo or control surface failure. This could include wiring or power to the servo.
Incorrect C of G or something in the plane shifted and changed the C of G.
Stall is always a possibility, especially given the high bank angle, but if the level stall speed truly is 8 or 9 m/s, then this still should have been okay. But if there’s been any changes to the weight of the plane this will change the stall speed.
