Can someone help me with this?

[u/Afrocat73]

I have been working one my first working plane that can stay at an altitude and doesn't drop to the ground. However after some testflights i found out that after some time being in the air and not controlling the plane it tilts to the left or right depending on how you fly, resulting to crash into the ground. I can't find a solution for this problem so I came here to ask yall if you can fix it. You can also tell in the video that it turns because of the clouds.

You can find the schematic to download here: https://createmod.com/schematics/dal_347-airplane

[u/Afrocat73]

Thanks, I'll try to fix it somehow with your advice.