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.

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That's not normal. Try another sensor. I get mine here http://rctimer.com/product-865.html for $16 free shipping.

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. 

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.

@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!

I always do a calibration because as the board warms up there tends to be some drift. This is especially true for the baro.

How did you generate that graph? Thanks!

Raph said:

Hi Scott,

Thank you for your input. Are you aware of a good way to check if the airspeed sensor is badly tuned? I ran through the calibration as directed; on the ground it shows a value of 3-4, and if I blow on the tube it does increase..

I attached a graph from the crash showing altitude, GPS speed & airspeed. To an untrained eye (me) it looks ok? I also increased my FBW min speed as well..

Typical stall, one wing drops, then spiral.
The ONLY way to get out of a spin, is DOWN elevator. Yes, it sounds crazy, but it will work. Also, use RUDDER, not alerions. Once spin is stopped, reduce power, then up elevator, alerions, as normal.

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