Ailerons on most aircraft only take up about 10% of the total wing area. Use darock's proportions, and you are into that range. Larger aileron area is found on aircraft that are more aerobatic. On some very small and very slow 3D-type models the aileron area is almost 50% of wing area. With slow speeds, you need large area for the control surface to be effective. Very fast models don't need large surfaces with large deflections to be very effective...witness pylon racers and jets.