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.
just a correction - double checked my params and STALL_PREVENTION was enabled (set to 1) when this crash occurred.
I've had this happen more than once in the past (before stall prevention was added). If you switch to manual fast enough you can recover.
Since you had it happen with stall_prevention enabled, you either didn't have your airspeed sensor well calibrated or your min speed is set too low. The airspeed sensor is not super accurate, especially at low speed so you need to give it a few MPH of margin.
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..
I did not perform a preflight calibration - on the field I'm using a tablet for telemetry; im not aware of a way to do this calibration with the android app (haven't found it).. the wiki only gives instructions for mission planner.
Is there any way to enable this calibration on boot every time? Seems to be a requirement for safe flight.. i'm surprised it doesn't do that by default..
So the bottom line is, on the ground the airspeed should read 0? or is there a range that is 'ok' like 1-2?
I'm using the analog airspeed sensor. I didn't know I could use the digital one with the APM - is it worth it in your opinion?
I also use the analogue one but I never fly with a groundstation, so instead of doing that calibration I made a cover for the pitot tube out of heat shrink. I just leave the cover on while plugging in the battery, once everything's settled and ready for flight I take the cover off.
This has worked well for me.
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?
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?
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.