PX4 Fixed-Wing AUTO Takeoff — No Rotation Command on Flying Wing

PX4 Autopilot
1

We’re debugging AUTO takeoff behavior on a separate fixed-wing flying-wing test platform and are seeing an issue where PX4 never commands a rotation.

In AUTO mode with a standard TAKEOFF mission item:

  • The aircraft reaches the takeoff point correctly

  • Throttle commands behave as expected

  • Elevons remain neutral

  • No pitch-up or rotation command is ever generated

Manual and stabilized modes work normally, so control surfaces, mixing, and authority are confirmed to be correct.

We’ve tried adjusting RWTO_TKOFF, TKOFF_THR, and related parameters without any change in behavior, and the mission item appears to be set up correctly.

Relevant details:

  • Flying wing (no dedicated elevator, only elevons)

  • No airspeed sensor installed

  • Bench and ground tests performed with lowered takeoff speeds

What we’re unclear on is:

  • What exact conditions PX4 requires before commanding rotation during AUTO takeoff

  • Whether the lack of an airspeed sensor can suppress the pitch-up command

  • Whether flying wings are handled differently from conventional fixed-wing aircraft

  • Whether rotation commands should be observable during bench or low-speed testing, or if PX4 suppresses them until specific airspeed/attitude conditions are met

Documentation on the rotation logic and prerequisites for AUTO takeoff is fairly vague, so any insight into expected behavior here would be appreciated.

2

Can you share a log via logs.px4.io where you see the issue?

3

Note: We believe the crash occured around 26:31.5. We had set FW_TKO_AIRSPD to 10 m/s which it clearly reached before it crashed and yet no pitch command was seemingly issued before it crashed.

4

Before trying out mission mode the first time, had you carefully tried and tuned altitude and then position mode at all? If not, I would be very surprised if mission just works out of the box.