Many ARFS have horrible aileron design.
The lightest/quickest /most effective fix -for me --has been to strip the ailerons -then make sure they are straight - then add diagonals along the surface - that is - even with the covering.
1/8" sq spruce will work - or make ribs -in each diagonal and cap and sand flush- How it's done is of little import.
The covering will grab each one and make tiny torque boxes along the surface - You will see this when you try to twist them.
Finally lighten the AFT portion of the aileron as much as possible -that is from center to trailing edge.

The object is to make the aileron CG move forward--
Insure the control linkage is stiff.
I fly big ailerons on 33% models with one servo - no problems using this technique.
On this size model a servo such as JR's new 811 digital should work fine.
I put them on my new 1230"sq in model.