APM response to catastrophic air frame/wing failure?


All -- what do you believe is an appropriate response of APM (ArduPlane) to a complete air frame failure?

Over Thanksgiving break, I test flew an Experimental Airlines AXON build (in a remote, rural area). The plane was flying fine with default settings, and I flew from FBWA to RTL to Auto. During the Auto mission the main spar (an oak dowel) failed and the wings collapsed at around 300' AGL. The plane, as you might expect, took a nosedive to the ground. If my recollection is correct, I could hear the motor running at full throttle as the plane headed to the ground -- my guess in an attempt to pull itself out of the dive. I didn't have the time (or the reflexes) to switch to manual and cut the throttle myself.

Is there ArduPlane code that could somehow detect such a failure and cut off the throttle?

I certainly don't plan on this happening again -- carbon spar from here on out -- but you never know...



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  • If there was a reliable way to detect airframe failure, popping out a parachute might work well. Though this opens a load more questions about payload and parachute design.

  • Moderator

    Keep trying to fly is what I would want it to do, I have had two servos fail in flight in the last month, one an aileron and one the rudder neither a train smash but the autopilot kept things sensible for me. Manual and throttle closed should have been the immediate action drill there. Another great reason for keeping the traditional flight controller around. Do all the fancy stuff on your laptop or tablet and when the chips are down reach for the TX and get home in time for tea and medals.

  • 100KM

    Agreed with John here - I would prefer the APM assumes air frame integrity and attempts to keep flying at all times. I once had an aileron partially separate while about 2km from launch which induced huge drag and a Zoolander style inability to turn left at all (even in attempted straight flight it would drift right). Fortunately using guided mode I could command it to fly increasing and decreasing right turns which brought it back overhead where I could manually take over to land.

  • The more you fly, the better your responses will get. 300 feet should be plenty of time to switch to manual and cut throttle.

  • Developer

    With the exception of full throttle, APM already did the correct thing for such a failure. Meaning it never gave up and tried to fly the plane all the way down to the ground to try and minimize damages. That is pretty much all you can do with a critical structural failure.

  • A feature like this would be difficult to make robust. Any kinematic condition to sense a failure would likely need the opposite response from APM as would be necessary for stability in a non-failure condition (eg cut power in a free fall instead of increasing power to stop a stall). If this feature didn't work perfectly, APM would cut power at the worst possible time...
  • The APM would have to have an airframe supervisory sub-system to alert it to this kind of failure.

    Maybe in ArduPlane 37.6 ? ;)

    Seriously, even CF can break if the loads aren't designed correctly. I hate to hear of your flight failure. Crashing teaches us things and, in this case, I recommend a better airframe.

    Did the logs survive? Those will tell you the throttle output at the time of the failure. You should see the gyro values going nuts within seconds of the event.


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