The Fixed Wing is V-Tail with Wingspan of 1.6 metre and fuselage of 80 cm. It has Pixhawk 2.4.8 with 5200mah 4s lipo battery full charged with T motor 1250KV 1055 prop with wing incident angle of 5 degree and C.G. is balanced.
(Check Plane 1 image)
The Plane takeoff with full throttle given by pilot. The takeoff was done in 5-6 metre. as per TLog, the plane leave ground at 8-9metre/sec. as we can see in tlog. The Pilot did the Elevator Pitchup during takeoff + Climb. Before plane nose down to crash, the Pilot removed the finger from pitch joystick since the Plane was in Semi Auto (Auto Stabilize mode). but the nose went down and plane crash.
There was no Flight Log from F.C. All the helpful images are uploaded. The Tlog2 image labels are assumed as per the video and Lines on tlog. Also check the video.
Couldn’t find cause of crash since, all connections, all control surface, C.G. was perfect and no loose assembly.
It may be harsh to write this, but are you sure that plane was aerodynamically stable with the flaperons?
It looks like the flaperons were fighting the elevator and when the elevator went neutral, the flaperons won and crashed the plane.