I have built a VTOL from a X-UAV Clouds Airframe with 4 lifter motors and one pusher at the tail. The plane flies well in MC mode and also Fixed Wing mode. Some transitions went well, some didn’t. I am only concerned about transitions to fixed wing flight. Back transitions always work without a problem.
The problem with forward transitions is that the plane always pitches up when I flick the switch. When it’s windy (and the nose is pointed into the wind) it can even end up in half loop. In the log files I have found the following:
You can see the offset between Estimated and Setpoint Pitch. I always have this offset, but the plane flies perfectly level in MC mode. When I flick the switch for the transition, the green line shoots up to zero the Pitch Setpoint. But the Pitch angle already was actually zero, which means the plane pitches up. Then the wind catches it and flips it over. This one ended in a very soft crash without any damage in high grass.
Here is another graph from a transition that didn’t end up on the ground but also showed a significant pitch-up tendency:
My gut feeling tells me I need to get rid of the offset between the green and red line which means working on the Level Adjustment.
Btw, in a level multicopter hover with absolutely no wind, the artifical horizon in QGC is not level. The plane hovers level in Manual and Position mode without stick inputs (as long as there is no wind).
Please help, I am a bit out of ideas at the moment.