Differential Throw Ailerons
Ailerons that are set up to deflect more in the upward direction than downward are said to have Differential Throw. The purpose is to counteract Adverse Yaw.




Radio controlled aircraft with ailerons can benefit from differential throws of ailerons. Aileron differential means that the aileron that moves upward needs to be deflected by a larger angle, and the one that moves downward is being deflected by a smaller angle. This results in a more coordinated roll of the aircraft because if the aileron throws were the same, the equal angle of downward deflection causes more drag than lift for the upward moving wing, slowing the wing down and causing the aircraft to yaw in the direction opposite to the desired direction of turn (if any).
     While desirable, differential aileron throws is not really a critical flight function and is not implemented in many lower-cost computer radios. And, of course, it is not at all available in simple, non-computer radios. And if you sensibly choose to drive both ailerons with one servo then transmitter programming is of no use at all.
     There is a simple way of accomplishing differential aileron throws mechanically, by positioning control horns away from the hinge of the control surface. On this page we provide simple charts that allow one to measure and position aileron control horns to get precise maximum throw angles while achieving the desired differential.

To use the charts, first make a note of the deflection angle you need and of what percentage of the upward deflection angle you want the downward deflection angle to be (the differential). Next critical parameter is servo arm travel. This parameter is what you can change by placing the aileron linkage in the different holes in the servo arm.
 Next, follow the links in the table below to find the servo arm travel that will enable you to select the horn offset and clevis height, while giving the desired deflection angle and percentage of differential. Make sure that you use charts for the same servo arm travel.
Source: http://www.rcmix.com/diff_ailerons.html