Mike:

Standard servos are fine on the Duellist 2/40. All surfaces.

Regards ailerons/flaperons. Never felt the need, But since the wing is mostly completed you still have the option of using two servos in the middle, linked through the torque rods, and you could program flaperons if you wanted to try them.

If you make split flaps I would strongly recommend using four servos, and mixing the ailerons into the flaps. At low airspeed with high throttle the propwash will hit the inner portion maintaining aileron control, without the mix you will lose roll authority at these same low airspeeds.

Bill.