Mixed Horizontal + Vertical Takeoff/Landing in One Mission on a Tailsitter + FW AUTO Takeoff Pitch Issue

PX4 Autopilot
1

We’re developing a tailsitter VTOL and are trying to confirm whether PX4 can support a particular mission profile. The aircraft needs to perform both horizontal and vertical takeoffs and landings within the same mission. In other words, the mission would look something like:

  1. take off horizontally as a fixed-wing,
  2. later land vertically in VTOL mode,
  3. take off vertically again,
  4. and finally land horizontally as a fixed-wing.

All of this has to happen on the same airframe without changing configurations or uploading a new airframe type. From what we can tell, tailsitters in PX4 default to VTOL-style takeoff/landing, and it’s unclear whether the TAKEOFF mission item can ever trigger a fixed-wing runway-style takeoff on a tailsitter. We’re trying to understand if PX4 can switch between FW and VTOL takeoff/landing logic mid-mission, or if the system architecture only supports VTOL-style sequences for tailsitters.

Our second issue is with a separate flying-wing test platform we’re using while debugging takeoff behavior. When we run a standard fixed-wing AUTO takeoff, PX4 never commands a rotation. The aircraft reaches the takeoff point, throttle behaves correctly, but the elevons stay neutral and no pitch-up command ever appears. Manual and stabilized modes work normally, so the surfaces and mixing are fine. Adjusting RWTO_TKOFF, TKOFF_THR, and similar parameters hasn’t changed the behavior, and the TAKEOFF mission item is set up correctly.

The flying wing has no elevator (only elevons), and we aren’t running an airspeed sensor right now, but we don’t know if either of those should prevent PX4 from sending a rotation pitch setpoint. The documentation is vague on what conditions must be met before PX4 actually commands the pitch-up during AUTO takeoff, and whether flying wings are treated any differently. We also aren’t sure if this should be visible during bench/roll testing (with lowered takeoff speeds) or if PX4 suppresses pitch commands until certain airspeed/attitude cues are present.

So in short, we’re trying to figure out:

  1. Whether PX4 can mix FW and VTOL takeoff/landing modes within a single mission on a tailsitter?

  2. What the expected behavior is for AUTO takeoff pitch-up on a flying wing, and what prerequisites must be satisfied before PX4 outputs a rotation command?

Any clarification on these two points would be much appreciated.

2

That’s not something that is currently supported pretty sure. It would require some changes/hacks to enable this. @sfuhrer can correct me if I’m wrong.

I can’t comment on the 2nd question, I’d suggest to create a separate topic in the forum and remove it from this one, if you can. The questions are very separate, so a thread about both would get very messy.