I have a Yaw, Roll and Pitch servo in my Kitfox S7. The Roll and Pitch servos can be hooked up to electric trim if your aircraft has it, mine only has a trim on the Pitch.
It's wired through 11,12,13,14 on the servo and runs through an expensive electrical box, then to the electric trim motor on the horizontal stabiliser. So it can command the trim motor as it requires, I'm guessing to save on load on the GSA28. With the auto pilot on or off I believe I can still manually trim via the stick through the eclectic trim.
Finally my question. This is an option so do I need it. It's about $600 bucks.
Thanks Lyndon