HELP. Level Calibration issues, FBWA will always dive

The airplane is a RVJET, that has previously successfully flown several autopilot missions and rock solid LOITER circles in moderate wind a week ago.
It is running Arduplane 3.0.1 (as this was the only firmware that worked properly with minimosd)
And we have just finished doing 5-6 test/tune flights. We were just getting ready to go further by adding ozone sensor and etc, and we crashed pretty hard.
I have tried to analyze my log, and found that it never really went into manual as I was fumbling with the mode switches. While the cause of crash is mainly pilot error, I am completely puzzled as to why the FBWA mode was pitching the plane down 10 degrees.
We had trouble with the autolevel FBWA/AUTO/Loiter mode since the maiden. We initially leveled the plane with the wings perfectly level on a table. then, we found that the plane liked to go into a 20 degree dive with that setting. Adjusting AHRS_Y to the maximum value of +17 would slightly adjust the dive to 25 degrees. So we would calibrate the level with the aircraft at near 20 degrees up position, thinking that the aircraft liked to fly with a slight up elevator.
This worked for a little while, and we had successful 3-4 flights in auto mode, with successful failsafe RTL and every other mode.
So we decided to put the POM ozone sensor, to test its readings and CG was set correctly, right where the vertical stabs meet the wing.
Preflight went perfectly, elevons behaved as needed, and we launched in manual mode with a bungee cord.
We engaged loiter as I reached altitude of 150ish, and loiter was not holding, and was decreasing altitude. So after loiter changed direction as the wind pushed it, it lost altitude even more because of a 10 degree dive, I attempted to take over. Went into FBWA mode accidently opposed to manual, and even with full elevator input (as seen in the log), it would not pull up. and it made a nice crater in the ground.
If any of you guys could help in analyzing our setup and tell us how to get the FBWA to work reliably, that would be greatly appreciated. I fully intend to put the manual mode into a dedicated switch, which I can pull in an emergency.

I should mention I have setup the plane in accordance with the arduplane wiki/manual at
and have followed every step leading up to the RTL test

I am new to arduplane, however, I have successfully setup dozens of arducopters.
The log is rather large, at 25mb, it is hosted on my google drive. … sp=sharing

Thank you very much for the great community/software.

Biggest question that I have is, why is the autopilot trying to go into a 30 degree in FBWA & Loiter & RTL mode, when I have leveled the aircraft with the bottom surface of the wing level with a table.

Is there a step I missed in calibrating the accelerometer?

The RVJet flies pretty much level with very slight deflection of the elevons, so I am puzzled why we had to calibrate the level with 20-30 degree nose up to get the FBWA & loiter to fly somewhat level.


Hi Maximus,

Can i suggest that you don’t attempt to manually adjust the horizon for the autopilot in the way you are describing as all the APM software is not designed to work this way (although I am assuming the APM/Pixhawk is located central and level inside the aircraft). Levelling should be done by trimming control surfaces and then adjusting the PIDs that the APM uses to maintain control.

Are you 100% sure that the direction of controls is set correctly in the APM Parameters? If you put the aircraft in FBWA do the controls move in the same direction as they do in manual in response to stick inputs?

If so, I would suggest you start from scratch on the trimming/tune as below:

  1. Fly in manual and use the TX trims to find a good neutral level flight trim.
  2. Mark position of control surfaces, reset TX trims and adjust servo arms to match the control positions that worked.
  3. Confirm nice level flight in manual mode with zero TX trim and the control surfaces in new positions.
  4. Do accel calibration and radio calibration on APM/Pixhawk and try FBWA (after confirming controls move correctly in FBWA as per Manual mode)

I hope that is helpful - happy to discuss further. Good luck!