Strong yaw when switching from QSTABILIZE to FBWA

ArduPlane Plane 3.7
1

Hello,

This is a QuadPlane running APM:Plane 3.7.0. I’m trying to transition to fixed-wing. When I switch from QSTABILIZE to FBWA, the forward motor turns on and starts pushing forward, while at the same time the plane starts yawing to the left. Since this is a flying wing, it doesn’t lend itself well to correction. Eventually, with both sticks full right and after a few seconds and close to a 180deg rotation, the yaw slows down and stops. I usually then revert back to QSTABILIZE, no transition.

Is there any reason for the flying wing to yaw in such a way when the forward motor is turned on?

Here’s the BIN log (5MB): https://drive.google.com/open?id=0Bz8Gb5bfp9T2SWZveGFmN2FwdGs

2

I thought about this some more. Since this is a small flying wing, could this be due to the forward motor (push prop) being slightly misaligned with the longitudinal axis of the plane?

3

Also when switching from QSTABILIZE from FBWA, I had noticed my aircraft was losing a few meters of altitude for a few seconds when the forward motor fires up, and here’s what I see in the logs

Screen Shot 2016-09-19 at 2.21.37 PM.png3168×700 22.5 KB

Can the drop in current be be caused by the spike in voltage to 14.5V somehow?

I have a 4S 5.2Ah battery, 10C - 20C.

4

Anthony,

Was your flying wing set up initially with APM Plane without a QuadPlane? In other words, did you initially fly the wing using APM Plane “Manual” mode, set the trims and record in TRIM_AUTO before flying with FBWA?

I have found it easiest to set up the plane with APM first and then convert to a QuadPlane.

5

Greg,

Unfortunately not. It was built as a QP from the very beginning.

I was suspecting a lack of power and I tried with a 35-70C battery, which didn’t help much.

However what helped was to do QSTABILIZE -> QLOITER (or QHOVER) and bring the throttle down to 10-20% -> FBWA.