To help reduce the likelihood of wing tip stall and adverse yaw, engineers developed differential ailerons. As the name implies, they deflect by different amounts: When the stick or yoke is moved to the right, for example, the aileron on the right (descending) wing is deflected up much more than the left (ascending) wing’s aileron is deflected down. This basic design is depicted in Figure 2, at right.
The reason differential aileron movement works is that deflection of an aileron upward can’t do much harm; it is the aileron deflected downward that can be the “troublemaker,” i.e., the one possibly precipitating a wing-tip stall. Additionally, a design incorporating differential aileron deflection works to minimize adverse yaw, the tendency of the ailerons to pull the airplane’s nose around to the opposite side of the intended direction of turn.
