Caution! Safety Issue - Quadplane will takeoff if armed and in mode RTL

Hi fellow quadplane flyers and devs.

Today we tested the behavior of quadplane whilst armed on the ground. When it is switched to RTL the quadplane will instantly try to takeoff at full throttle. As mentioned previously on other threads, this is the same behavior it has in SITL as well, so I held down the quadplane safely in expectation of this.

I think this is quite dangerous as any cycling through the modes on the RC will launch the aircraft if it is armed. Especially larger quadplanes this could lead to very dangerous scenarios, where the pilot or others are still to close to the airframe prior to launch, or where the wrong mode is selected inadvertently. (eg some RC swtiches cycle thru)

For safety reasons the only mode that should really trigger takeoff is Auto. RTL is typically only used to get the aircraft to return to launch, but not to takeoff. Also I’m thinking that the current 6 modes available for selection should be expanded so that both Q and plane modes are available at the same time to allow for either quad or plane mode recovery by the pilot.

On a unrelated matter, we are also experiencing intermittent attitude control issues in qloiter, qhover and RTL, which cost us one of our test air-frames today. After a unspecified time the aircraft will pitch forward sharply without warning. the crash occurred after switching from auto to RTL.

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Hi Jeff,

I haven’t tested this RTL auto-launch bug, can you give me a little info about it so I can duplicate and fix quicker?

Was there a mission loaded?
Did the mission include a TAKEOFF?
Did the mission have a QLAND?
Did the mission have a DO_LAND_START?

Did you boot in a non-RTl and upon switching to RTL is when it launched?
I assume you were already armed when you manually switched to RTL, is that right?
Do you know if this happens if it auto-switches to RTL via normal failsafes?

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Thanks for the heads-up. I also experienced this on my Bix3 QuadPlane when my initial Flight Modes were set to have position 6 at RTL instead of Manual. Fortunately, I didn’t stay on position 6 long and I wasn’t near the plane. The forward thrust plane prop was also off. I was simply armed and I was going through the flight modes.

I would like to hear more about your thoughts on the 6-position Flight Modes. My experience with APM: Copter and the FireFLY6 tiltrotor and CL-84 tiltwing have made my perspective think that a QuadPlane is first a copter and second a plane. However, the QuadPlane implementation in APM Plane has caused me to re-think my learned perspective.

As a suggestion, it would be nice to add flight modes outside the 6-position switch on channel 8. The copter implementation allows for RTL to be on channels 6 or 7 tied to a transmitter switch. This is how I use it on all my multi-rotor copters, both APM and DJI.

Also, on my FireFLY6 and CL-84, the bailout mode when in trouble has always been to go to hover mode alt. hold (or QHover) not a manual plane flight mode.

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Even pressing the hardware safety switch won’t prevent an inadvertent take off if the a failsafe occurs. I put it here on github. These are serious safety issues.

Hey guys!

@tridge and I talked about this at today’s weekly dev call and it comes down to a few issues happening: one is that the is_flying check is now much more complicated on quadplane than it is on regular plane and that was just recently improved and will be in the next release. Next is that RTL is an AUTO mode so it works just like auto. If you had set it to AUTO then it would have done the same thing, right? We agree there should be some extra protection on RTL so we’re going to put in a few extra precautions.

Hi Magicrub
Thank you for the quick response to this.
A few answers to your questions:

  1. Mission was loaded, including Q_Takeoff, Q_Land, Q_Transition, DO_Jump (at end to repeat course 4x) and Do digicam triggger distance.
  2. No DO_LAND_START was used
  3. Booted in non-RTL mode
  4. Because I had tested this behavior in SITL many times (In fact I used it to relaunch the missions in SITL because it was easy!) we wanted to check if it had the same behavior on our real quadplane. As a result I was holding the plane down safely to test it.
  5. It only happens if it is armed. We had it armed to test.
  6. We haven’t tested the behavior on failsafe, however that should be possible to test on SITL.

In regards to your comments about IS_FLYING: From a experienced user’s point of view this might be acceptable, however currently, quadplanes is only some 6 months old, and those converting from plane, or even copter, will not consider this “normal” behavior for RTL. The first level of protection should be to ensure safe and predictable behavior, so getting this fixed as soon as possible, along with maybe a warning in the wiki until it’s fixed would be a prudent way forwards.

In regards to the Q modes in general, I’m also thinking that and alternative solution would be to add a separate parameter to trigger takeoff, that would continue to allow any “auto” mode to initiate takeoff like it is now, but will force new quadplane users to familiarize themselves and use an extra trigger to takeoff. I think this would also fit well with a “pause and resume” function.

BTW there’s also another issue regarding landing that I’ve explained here that probably needs to be addressed to avoid flyaways/crashes: Quadplane landing issue using weathervaning, Quad hover and forward motor simultaneously

Thanks again for the fast response and all your work.

Thanks for the explanation but it doesn’t address why the hardware safety switch won’t disarm the quad motors.