Kerosene jet with Arduplane crash analysis

For a project that involves fast, low flying jets, we set up an APM running Arduplane 2.74.

We used EZUHF for the RC link which was programmed to trigger RTL if the RC link got too weak or lost.

What you can see in this video is the Mavlink data using Minim OSD during the auto waypoint flight. At 1:10 the link starts to cut out and the APM switches to RTL. However, the link does come back a few more times, switching between Auto mode and RTL. At 1:50 the pilot invoked RTL via RC link to make the jet fly back home.

At this point however the jet dives and does not recover.

https://www.youtube.com/watch?v=BPzfmc1vWXQ&feature=youtu.be

Unfortunately our telemetry link died after 3km, so our recorded logfile is only useful for that part of the flight:

https://dl.dropboxusercontent.com/u/18031607/2014-04-12%2019-07-50.tlog

Based on what we can see in the video, we are assuming that the APM might have frozen up since the artificial horizon stopped working as the jet started to dive. But it might as well have been the MinimOSD that was lagging behind the data.

Of course considering the speed at which the jet flies, it is entirely possible we have been on the limit with the APMs processing power but we had multiple RTL runs that went flawlessly before this accident.

If anybody has ideas or suggestions on what might have failed, please post it here or feel free to ask any questions I might be able to answer.

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  • First the video was painful to watch. Were you able to recover anything?

    Looks like perhaps the magnetic compass was off. Here are a couple  screenshots of your telemetry. Is there a chance that APM came loose or something caused magnetic inference?  With the compass being off the APM may have tried to correct. The red line is the magnetic heading and the black line is the gps heading

    Also what antennas are you using for the EZUHF? You should have gotten better range with EZUHF. Out were you were flying you should easily get 10-15 km if not 20km. Also did you have any other equipment running like RADAR? Also which frequencies are you using for telemetry? I wouldn't use 433mhz telemtry with EZUHF.

    I would investigate things that can interfere with the gps and magnetic compass. I would also use a spectrum analyzer to see what devices cause rf noise such as the Jet Engine computer. 

    Another cause could be the plane lost elevator control somehow. Hard to tell from the limited telemetry data.

    3701708494?profile=original

    3701708741?profile=original

  • It's for testing a radar prototype for our university. The flying area is a dedicated area for this purpose and there are failsafes for the motor Ecu that are triggered should there be any indication of a fly away.
  • Could you please share with us the context of your project involving autonomous high-speed low-level flight of turbine-powered aircraft? Thanks! 

  • Yes, AHRS got messed in the end.
    Wonder of gforces could have played a trick here.
    Speed does not influence cpu usage.
    Was GPS sane until the end ?
    Any chance of recovering .log from APM ?
  • Developer

    the apm was still responding, as the alt,roll and pitch where all responding, you can see this via the osd.

     

    but it does look like the attitude solution was messed up.

    watch the pitch, its at +38 degrees even though its pointing at the water.

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