Increasing horizontal speed decreases altitude

Hello everyone,

I am using a custom tilting multi copter airframe dervied from px4 multicopter.

Everything is working fine as required, however when i increase speed beyond 20 m/s the drone starts to lose altitude and then crashes. Do suggestions or advice on what should i look for?

you can start with checking if the altitude estimate is correct.
(you are welcome to post some logs as well)

please see the logs if you can make sense of it. Z distance drops downs and I have to land it

ok, so at the point where Z starts to deviate from setpoint there is a sharp jump in pitch (at ~1:17):

you can see quite clear what happened from 3d view:
at ~1:17 the drone does a nosedive, then it tries to recover, but loses altitude and eventually tumbles.
I think it’s not able to recover well because px4 might be not well tuned for tilting motors? the velocity is also quite high to easily recover.
did you set up and tune px4 for your frame?

I not an expert on aerodynamics, but i think the nosedive is because of aerodynamic instability. as soon as rear motors slightly overpower front ones, the frame can easily swivel so that rear motors rush forward, and flip the frame. I think that at this velocities you need some sort of stabilizers/wings for a tilting platform? that might be the trick.

bu in any case, great job at getting it to fly at all, and working on a challenging platform, quite inspiring!

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Thank you for the analysis.

Yes, the drone is tuned and it works perfectly well for speed under 17 m/s and sometimes even at 20 m/s.

I’ve tested it with a smaller drone and i get around 25 m/s without crashing. So I’m thibking the issue has to be with my airframe design.