This was my first flight tests using IMU stabilization insteed of thermopile sensors. After some PID adjustment I have nice and stable stabilization of the airplane. But... Whenever I accelerate quickly the plane goes into a dive. Or if I decelerate it pulls up. The plane is trimmed and motor mounting angle is good, so it is not that. It does not seem to be a problem with vibrations. I have mounted the IMU using vibration pads, and if I slowly accelerate the IMU maintain the correct pitch at any throttle setting. Same with deceleration. But punch the throttle and the plane goes into a steep dive. Or sharply pulls up if I let go of the throttle quickly.
My setup is the ArduIMU+ V2 with unmodified v1.7 firmware and the ublox gps.
I am currently focusing on stabilization so the only autopilot logic in use, are PID loops for elevator and ailerons using roll and pitch from the IMU as input.