Dave:
Its called differential ailerons.On a flat bottom wing, the down going aileron has more drag than the upgoing aileron, called adverse yaw. The drag on the down going aileron, say, to do a right turn the left aileron goes down but the drag on it is trying to make the plane turn left. One way to fix it is to put a servo wheel on the servo. drill two pushrod holes forward of where they would normally be, maybe 1/4 in. forward of the cross centreline. Now you can see where the holes move a shorter distance when the wheel moves forward and a longer distance when moved toward the back. Two servos and a computer radio is an easier way, but this way works fine with one servo. Hope it's not to confusing.