Find out why the VTOL crashed

hi guys, my VTOL suddenly crashed during the flight. I didn’t find the reason from the logs, any reply would be greatly appreciated.

flight log

Open up the access to anyone, we cant download the log

And post it on the correct section.
Are you using ArduPlane 4.0?
Which hardware?
Which firmware version?
What manouvers where you doing?

Thanks for the tip, I use firmware 4.2 and CUAV X7 hardware.

Hello guys I’ve tried a maiden fixed-wing flight from Qloiter through the FBWA but failed three times during the transition. The first one did not reach to transition and I stopped it manually. On the second try plane started to rotate in yaw uncontrollably and the final, last try made weird moves when I turned back to Qloiter probably because of the batteries moved inside of the plane, and crashed to the ground. I am adding logs and videos of the transitions
. Can you help to diagnose the problem?


You should first carefully read the QLOITER and TRANSITION documentation.

When transitioning from QLOITER to FBWA, both thrust control and VTOL attitude control are applied to the forward rotor until airspeed reaches ARSPD_FBW_MIN. If the aircraft yaws to the left due to the difference in tilt rotor speed during the transition, the VTOL controller will increase the speed of the right forward rotor in an attempt to make it yaw to the right. However, since the rotors are tilt forward, the aircraft will accelerate yawing to the left.

To solve this, you need to increase horizontal speed to around ARSPD_FBW_MIN before starting the transition. Your configuration has Q_LOIT_SPEED=500cm/s and ARSPD_FBW_MIN=19m/s. You need to bring these two values close together.

Hi @hatnac thank you for your reply.

I know my plane does not reach to minimum transition speed but my point is “why” it has not reached. I made some tests in realfligt and find out a safe flight speed which is why I made ARSPD_FBW_MIN to 19 m/s. Also, I tried three times on the same flight but every try ended with a different attitude.

About the Q_LOIT_SPEED it is around 5m/s yes but do I know the wrong Arduplane hold tiltrotors at some middle angle which is 45 degree in my case and try to reach the minimum FBW speed. So I can’t decrease the FBW_MIN does that really mean something to increase the vertical flight speed?

Your aircraft is not reaching the minimum transition speed because Q_LOIT_SPEED is set to 500 cm/s. I think the problem is that you are transitioning to FBWA with a slow horizontal speed.

My suggestion is as follows:

  • Set Q_LOIT_SPEED to a value close to ARSPD_FBW_MIN. For example, 1600 cm/s.
  • Increase horizontal velocity in QLOITER mode with pitch control stick.
  • Switch to FBWA when the aircraft reaches a speed sufficient for transition.

Thank you I will try your suggestion. Thank you but I am still open to new suggestions. I am really afraid to fall down one more time.