Fixed wing plane pitch issue and doesn't land

#1

Hi guys,
I have a problem with my twin motor airplane.
The airframe is a Believer FPV with V tail and I used the Applied Aeronautic Albatross as template for the correct mix and moving part setup.

The plane fly overall good, I have a small issue on pitch that I can’t figure out, where it keep be bouncy while travelling between waypoints, when climbing and staying flat. I don’t think it’s something related to PIDs since when I fly in stabilize it’s perfectly stable.

The biggest problem I have is that the plane doesn’t land, I mean, it loose the altitude perfectly to approach final on landing, but when it exit the circling of sink it stay flat without loose altitude anymore. It’s expected to put the nose down on approach, but it just keep altitude and overtake the landing point, then I take over manually and land it.
It has Garmin LidarLite V3 onboard as rangefinder, someone can help me with those 2 issues?

A flight log as example is available here:
https://review.px4.io/plot_app?log=79e74c1a-6622-4f86-a10c-f66b0e3af8f9

Thanks

#2

Hi @Damiano_Maeder ,

Given that throttle and pitch oscillate. I guess it’s a TECS tuning issue; did you tune it? There is a pending or the tuning guide here: https://github.com/PX4/px4_user_guide/pull/475/files?short_path=02de973#diff-02de97315e248e0023859bb437f59daf
Also, I’ve seen that your gyro cutoff frequency is at 80Hz and there are quite some strong vibrations just above that. I would suggest to reduce that value to ~50-60Hz. This will reduce the noise you feed back to the actuators and thus increase the life time of the servos.

Good luck!

#3

Thank you! I’ll give a try following the guide and report back, thanks!

#4

Hi Bresch, another question, do you know also why the plane doesn’t sink to land on final approach?

#5

@Damiano_Maeder No, sorry, I’m not familiar with the fixedwing takeoff and landing logic.