I used a standard servo connected to torque links for the bottom ailerons which in turn were connected to the top ailerons via slave rods. It's a very common method used on biplanes with four ailerons. Sometime about 30 years ago people began using a servo for each aileron. While I think that is overkill for small biplanes 60" span and under, but probably necessary on bigger biplanes. Especially ones used in IMAC competition. Those are typically larger than 25% scale and heavier than 10 pounds.