ORIGINAL: bruce88123
There could be a lot of reasons why this is happening. One could be the "neutral" or "center" position of the arm on the servo. Another could be not having the horn positioned correctly in relation to the hinge line of the aileron. For most high wing/sport plane a little "differential" is nice in the ailerons BUT in the other direction. This is because it helps prevent adverse yaw during turns. This is also used in full scale planes.
Desirable = more up than down.
Can you post a pic of your servo installation and linkages?
on a flat bottom wing(trainer or cub) the aileron going down causes more lift and rolls the plane. I.E. down right aileron is rolling your plane left. if your plane handles well with the diferential it curently has your good to go
