[redxfred]

We can trim the Hurricane for coordinated straight and level flight, but without an autopilot or "Wing leveler", it will naturally "Upset" and start a turn after a while. This is a design characteristic of all high performance airplanes which enables them to roll more rapidly than stable trainer types. You just have to constantly fly the plane.

You should never have to fly around in a slip... that's like flying sideways all the time. It almost sounds like your aileron control is causing an uncommanded roll. You could try unplugging your joystick, then trimming it up with the keyboard commands only. If that works for straight and level flight, you may have a joystick problem. Good luck.