I am a beginner pilot, so I am not sure if this is pilot error or Plane error.
I have had two crashes the same week caused by the same problem, last time was yesterday. I am flying a Bix3 with a Pixhawk (without airspeed sensor). Yesterday I flew for 30min on one battery without problems, did the Autotune again since I wanted more iterations than last time (this time I did 80 roll and 80 pitch iterations).
Takeoff on first battery was very nice, I used full flaps and full throttle. I haven’t thougth about it before, but reviewing the logs it seems that the plane is climbing nicely without me adding any elevator. After climbing a bit a I retract the flaps completely, the plane pitches down a bit (from the sudden loss of lift I am guessing) and I pull back on the elevator to bring it back up. Nothing dramatic.
Takeoff on second battery was not good. Same as before, but this time I reduced the flaps to half some time before retracting them all the way. When I retracted the flaps from 50% to 0% the plane went into a nosedive, I input max elevator, but the plane keeps on diving for 80m until it crashes in the most spectacular way, sending styrofoam, battery, camera, wings everywhere.
I am mostly thinking that this is an aerodynamic phenomena from me retracting flaps at “high speed”, but I am not sure.
I have seen that another user here has posted the same problem here, so I thought maybe there was something else to it.
Anyway I am happy for help, even if it’s just pointing out the correct way of taking off with flaps
The first one is the successful flight, last one is crash.
P.S.: Flaps are on channel 5, elevator is channel 2, aileron is channel 1, throttle is channel 3.