APM 2.6 - AP3.2.3 - Spiral of death in FBWA

Hi Everyone,

Very weird crash today. I have 12-15 flights all flawless before this incident. When it occurred I immediately thought I lost a servo - but upon inspection both servos were fine. Watching the video (below), I did not input the left roll that began the spin. I tried to switch to 'manual' but that made no difference; it's like I had no attitude control what-so-ever.

-APM 2.6 Plane 3.2.3, GPS with external compass
-3DR power module
-APM airspeed sensor

Here's a video of the crash - winds were about 10-15mph hitting the aircraft from the right side. I left the sound in, so maybe lower your speakers before clicking the link:

Attached are both the telemetry log from ground station & dataflash log.  

Any help would be greatly appreciated! Trying to rule out the autopilot as the cause before venturing back out. It almost looks like a stall, but I'm doing at least 20mph when the spiral begins.. I've flown this plane at 10-15mph without any issue.

logs.zip

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                • Hi Mark,

                  I also keep a foam cover over the pitot tube when powering up - but as iskess mentioned i guess it doesn't make a difference as the calibration has to be done manually anyways?

                  • @iskess thank you that's the exact airspeed sensor I have right now (bought from 3DR). I'll order a replacement one from rctimer to test out. very weird though, today I could not make the AS jump again by putting my finger over the pitot. must be faulty..


                    @MarkM thank you for the link - I did read that, but was getting conflicting answers on if it does zero it out on boot on not.. i'm going to make a cover out of shrink wrap as you suggested, maybe the foam one I made is letting air through.

                    appreciate the help!

                  • Have a read of http://plane.ardupilot.com/wiki/common-optional-hardware/airspeed-3/ under calibration it says you are supposed to power up the apm with the pitot covered, if you forget then you use the mission planner calibration button.

                    So really, the mission planner calibration is the fall back method that you only need to do if you dont power up properly. 

              • The preflight calibration can't be automatic because it requires you to place your finger over the pitot tube to stop any wind. I use the analog with much success. I don't see more than 1 m/s at rest in any of my planes. If you zero it out it is very accurate. I don't know anything about Droid Planner.
                • I tried to run the preflight calibration, and I cannot get the airspeed value to be less than 2.8. It is fluctuating between 2.8-4.2 while sitting on the ground. Could it be a faulty airspeed sensor? 

                  • Mine will hover between 4-8mph on the ground and that's whether I use the cover and power up method or the MP pre-flight calibration button. Still work's fine i the air though.

                    Agreed though that covering the end of the tube should not make the airspeed jump up, just tried it on mine and it doesn't change the reading at all.

                  • That's not normal. Try another sensor. I get mine here http://rctimer.com/product-865.html for $16 free shipping.
                    Rctimer Airspeed Sensor MPXV7002DP
                    RCTimer - the world's, No1 Online Hobby Store. We stock a huge selection of RC products from Planes right through to Quadcopters and all accessories.…
                  • if I cover the hole on the end of the pitot with my finger the airspeed value jumps to 30, not sure if that's normal. 

    • Hi iskess,
      Thank you for taking the time. This is a Mako flying wing (no rudders) http://www.readymaderc.com/store/index.php?main_page=product_info&a...

      The aircraft was autotunded, which really made it fly quite nice. Also the airspeed was tuned as per the wiki. The FBW min is set to roughly 21mph which has been more than enough (maybe until now?) - this would be the first tip stall I've had on this frame. I did not activate the stall prevention code but I will now. I hope the logs substantiates your initial diagnosis; I'd much rather it be pilot error!
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