Crash Investigation, ArduPlane 2.28 on APM1

Hi everyone!

I need your opinion on why the following might have happened.

Last weekend I had a nasty crash with my EasyStar and APM1.0, using ArduPlane 2.28 and MissionPlanner 1.1.19. On that day temperature was between -10C and -5C, light wind and lots of sunshine. I had already completed two missions to take some movies which had gone absolutely smooth and as planned.

The last one didn't...3690915026?profile=original

 

The plan

As the sun was about to set, I loaded a mission I had already flown earlier last year. It's a steeply declining zigzag path, which would allow me to  take photos with the the plane banking hard, gliding without motor, to make sure photos came out as sharp as possible. The mission was uploaded to APM, then downloaded again to check everything was ok. Preflight check as usual in stabilize mode, everything seemed ok, so I got the plane in the air.

3690915086?profile=original

 

What happened

I climbed in narrow circles to about the altitude of the first waypoint, then I switched to AUTO.  The plane did a sharp turn, and then set out on a long leg to the first waypoint. Or so I thought, I didn't remember exactly where I had set the first waypoint, so I let it fly in the wrong direction for too long, before realizing there was something wrong.

The plane was already too far away and against the bright sunset sky. There was no way I could have revovered manually.  So I switched to RTH, but this only made the plane stall two times and then dive into the ground.

 

Reading the log

Fortunately the APM still boots up and I was able to recover the onboard log data. I don't have telemetry, so I have to rely on this data to get a better understanding of what happened. Most interesting is the attitude data from the log.

On climbing to altitude, attitude seems to be ok:

3690914945?profile=original

20 seconds before impact. Check the attitude data!

3690915048?profile=original

I could still see enough of the plane to know it was flying more or less level when the log data suggests a pitch angle of -50 and a roll angle of -35! What was going on there?

Here's just after switching to AUTO. Something must have happened that made the IMU sensors go completely wrong. Check the plane symbols on the white path and then on the green path. I can definitely confirm that the planes attitude was completely normal then.

3690915110?profile=original

 

What I want to know

  1. Temperature too low, sensors disturbed? With wind chill, temperature might easily have been down to -15C.
  2. Some software glitch that made the IMU recalibrate in the wrong moment?
  3. Cosmic rays, aliens?
  4. ...?

Break out your crystal balls and tell me what happened :)

I'd love to rely on APM in the future but I need to know its weak points.

 

Thanks for reading

Chris

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Replies

  • Something else

    I opened another thread regarding repairs on the IMU shield. I didn't get feedback there. Maybe someone with some technical knowledge of APM1.0 could take a look at it?

     

    Lessons learned

    • First of all, don't rely on your autopilot.

    I'm obviously not the only one who lost a plane to an autopilot system that went awry. I should remind myself of this more often :)

    • Don't let the plane fly out of your visual range on autopilot.

    Unless you are "on board" with video downlink, your spotter has really good eyes or you just don't care... :) In my case it was just too dark and I was a already a bit tired from the cold.

    • In AUTO mode, always know where the plane is supposed to go. The slightest deviation from what you consider normal should make you switch back to MANUAL immediately, land and investigate.

    As I wasn't absolutely certain on where my waypoints were, I let the plane go on for too long.  I was suspecting something could be wrong but waited too long to take the right decisions.

    • Concentrate! 100%! Gravity is against you :)

    I was slightly distracted by someone talking to me. Bystanders shut up, please.

    • Finally, trust your gut instinct. It's late, it's getting dark, you are tired. Take a beer, sit back, relax :) Just don't fly!

    It's not the first time that I wasn't totally sure if I should fly and subsequently crashed something. Might be ok with a cheap fun plane, but not with the more expensive equipment. I should finally learn from my own mistakes :)

     

    What did I miss?

     

    Fly safer than I did :)

    Chris

This reply was deleted.

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