No GPS VTOL transition

Had a few successful flights as well as a maiden with my VTOL tricopter based on the VAS Ghost airframe:

There were some weird behaviors that I was curious about. This is using only gyroscope/accel and baro. There isn’t any sort of velocity reading. When I flip from qstab to FBWA it does a nice transition, but the voltage remains pretty low. When I flip from FBWA to acro the voltage bumps up for the same throttle level. I didn’t think to enable logging, but will next time.

My guess though is that it can’t determine that it’s going fast enough to full transition and just maintains the back motor until I switch to acro. Any other hypothesis?

Hi Luca,

From the APM Wiki


Flight modes to avoid

The linked nature of of the vertical lift and fixed wing control in quadplanes means the autopilot always needs to know what the pilot is trying to do in terms of speed and attitude. For this reason you should avoid the following flight modes in a quadplane:

  • ACRO

These modes are problematic as the stick input from the pilot is not sufficient to tell the autopilot what attitude the aircraft wants or what climb rate is wanted, so the quadplane logic does not engage the quad motors when in these modes. These modes also make log analysis difficult. Please use FBWA mode instead of STABILIZE for manual flight.

Hi Greg,

I’m actually experiencing the opposite problem. Acro seems to work fine, but FBWA is being problematic. The excessive voltage drop (and therefore higher current) happens only in FBWA, not acro or manual. I will attempt to record logs this coming weekend. That should help determine what’s going on.


Hi Luca, did you find out why you were seeing a voltage drop when you transition from q stabilize into FBWA?

Hi Shef,

I did figure it out. Unfortunately I couldn’t log it, but I believe it was because of the lack of velocity measurement. Basically the rear motor would stay on and the front motor tilt servos would stay slightly tilted up while the front motors accelerated. Basically it tried to transition, but with no velocity feedback it would just stay at the halfway point. Going to acro instantly killed the back motor and transitioned the front servos fully. Going from acro to fbwa doesn’t have the same issue.

I can’t remember if I fixed it, or just flipped to acro after gaining some forward velocity.

Hopefully that helps a bit,


For reference, here are some more videos of this plane and my friend’s identical build flying together:

Yes it does help, thank you Luca. I’m making a dual motor tailsitter right now, I hope I don’t encounter a similar voltage drop during transition from Qstabilize to FBWA.

Nice flight you posted, the transition seems pretty seamless despite having to use acro mode; nice.