Drift with wind in Auto, not in qloiter?

I have a quad VTOL plane (q_enable =2 for this) that we were flying in stiff winds (15kts) yesterday and it would hold its place in qloiter, or durring a VTOL_Takeoff, but when it switched to VTOL Land it started to drift backward, unable to proceed forwards against the wind. Log shows the WP dist increasing and the Qtun.DAx and DVx max out. Q_Angle Max (10deg) was not met at all during the flight.

Any ideas?

Log posted:

I haven’t pulled your log file down but I’d suggest checking Q_VFWD_GAIN

Its set, and the cruise motor works. It uses it to loiter too, so I’m not sure how that would affect it, but I’ll put it in my battery of simulation tests I’ll do.

So in SITL I haven’t yet gotten this to reproduce, but its happend IRL multiple times, with multiple aircraft.

I tried toggling VFWD gain on and off, no change in SITL
I tried turning down Q_VXY_I/P, Q_PXY_P (a parameter we fiddle with and have turned way down for our landings) and got nothing in SITL either.

Still hunting for this, and hate to have to iteratively fly this to pinpoint the problem.

I’ve asked for some extra help: but to grasp at a straw, you don’t have any deadzones on RC in, and in land mode RC inputs are respected - so for instance the autopilot thinks you are commanding 1495, rather than having mid-throttle, which would let the autopilot control it. Try setting a deadzone around mid throttle (10 or 15 would be enough), and see if that makes a difference.

Thanks @james_pattison, are you talking about throttle nudge having an impact? Throttle nudge is off, and there is a small dead zone for qloiter, but in Auto I can do what ever I want to the throttle and it doesn’t affect anything (unless it somehow does in this weird way). I always go to 50% throttle when I switch to auto, in case I ever need to swap to qloiter for some emergent reason and then she’ll be ready to hold position.

Not specifically throttle nudge. During landing stick overrides/mixing are active so you can reposition if needed. As you don’t have any dead zones set, this might be contributing.

Ive got stick mixing on in general and haven’t seen anything like this except in high wind auto landings, but I’ll take a look. the log should show where the RC is at.

Did some testing with high winds and showed that turning up q_wp_speed, q_wp_loiter_speed, q_pxy_p, and q_vxy_p appeared to have no effect on this annomaly.

High winds tomorrow so we will attempt to flash 3.9.4 and see if it happens with that.

More testing today. Flashed 3.9.4 and it still happened.

@WickedShell any ideas?