Quadplane RTL/QRTL behavior at low altitude, Danger!

Hello all, I have a question regarding how the RTL/QRTL handover behaves when hovering at low altitude.

The aircraft of todays issue is a tiltrotor quadplane running firmware 4.0.5. After a long flight in AUTO mode, the aircraft was hovering to landing using a VTOL_Land mission item. However, the landing position was slightly off from desired, so the aircraft was switched to Q_Loiter to be landed manually.

At this point, the critical battery failsafe engaged, and put the aircraft into RTL at around 5ft off the ground. We do have Hybrid RTL enabled, and the aircraft was within the Q_RTL_Radius at this time.
I would expect, in this case, for it to simply enter Q_RTL and continue landing on it’s own with little issue.
However, instead, the aircraft entered “normal” fixed wing RTL for a brief moment, and began moving forward as if to transition to forward flight. It then changed to QRTL, went back to a hover, and landed.

I was able to replicate this behavior in SITL/Realflight sim testing, so it’s not a one-time thing. Any time I click “RTL” while hovering within the Q_RTL_Radius, the aircraft lurches forward in fixed wing RTL, then returns to Q_RTL and hovers back to landing. Since failsafes also switch to RTL mode, the same behavior would apply to any conceivable failsafe RTL occurrence, no?

Is this the normally expected behavior for Q_RTL? Is this correct? It seems dangerous to leave as-is. The aircraft luckily didn’t crash this time, but shooting off forward unexpectedly during a landing/hover could have some serious consequences depending on what it’s pointing at, not to mention crashing the plane. Any help is appreciated.

We have a open issue, I think its the same problem?

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That issue seems to be talking about tailsitters? My case is quadplane, not tailsitter. Might be the same root cause though, as the aircraft is switching to RTL mode for a brief second before going to the correct Q_RTL. The problem happens during that time, as RTL is a forward-flight mode for quadplanes/tailsitters, causing it to attempt to transition.

Yeah, its the same issue, I have PRs a fix

Tailsitter or not the issue is the same for all the VTOL.
With tailsitters it becomes more critical.

Same issue here. Found in Arduplane 3.x and 4.x

That’s great!
I hope it can be worked into a release soon. I have aircraft it can be tested on if that’s necessary. This seems like a pretty major safety issue for VTOLs, it could easily hit something during landing, so it’d be great to see it fixed.

I see the PR has been merged, and I just tested it to be working with my SITL/Realflight setup. Still waiting for a more solid numbered release to use before I load it on a plane, though.
There’s still a bit of concern if you try to RTL while hovering at a low altitude beyond the Q_RTL_Radius, but that’s not a condition I ever intend to be in while flying. I only use hovering for takeoff and landing. That being said, a system like “if hovering below X feet AGL and RTL is engaged, climb to above X feet AGL before attempting transition” would be nice for the people that use VTOL capabilities more freely.

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Exactly, this procedure would be more correct, but in any case it is already better than before.