Ok, i think i found the problem.. When i go full throttle with the controller, the plane is going sideways. Taking the throttle back make the plane stay in line. So its the controller that is the problem, not the joystick.
But what the he** should i do?
EDIT: After signing throttle to a different button, it didnt work to adjust the throttlehandle to make the plane not go left. Sooo.. im back to zero.
EDIT 2: I tried to re-calibrate the joystick and i discovered this: http://i.imgur.com/PvxWQSV.png - notice the X/Y Axes. Thats how it looks like when the joystick is centered. That cant be correct?