VTOL nose-up tendency during transition

Hi friends. I built my gas engine VTOL drone (quadplane) and I’m using arduplane 4.0.4. I have done many successful flights. But always I have an issue and I couldn’t solve it.
I take off in QStabilize or QLoiter mode and climb to about 30 meters up. After that, I switch to FBWA and set throttle to max and start to gain speed. But in first 5 seconds, multirotor motors starts to move the nose up and prevent the drone to move forward. After I apply too much pitch down by stick and it starts to move forward. If I don’t, the plane will collide with ground by tail and crash.
Another amazing subject is that I don’t have this problem in my electric VTOL drones and this issue just happens in my gas engine VTOL drones!!
What do you think about it?
Thanks for reading.

Nobody had this problem before?!

I’m familiar with ArduPlane but @GregCovey or @iampete might be able to point to a parameter setting that’s causing this. Normally, during MC to FW transition, you shouldn’t be putting any control inputs until the transition is completed. Hope they’re able to point you to the right direction.

Good luck.

Hi Kaveh,

I agree with rollys that you shouldn’t need to raise your throttle before transitioning to FBWA. It almost sounds like you have up thrust built into the gas engine mount.

I would recommend posting a .bin file of this issue. It will allow others to look at what the flight controller is doing versus the pilot input and plane response.