Two Aileron Types

To help reduce the likelihood of wing tip stall and adverse yaw, engineers developed differential ailerons.

Thursday, October 30, 2014 at 12:00 AM ET

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Key Takeaways:

Differential ailerons were developed to reduce wing tip stall and adverse yaw by deflecting the aileron on the descending wing upward much more than the aileron on the ascending wing downward.
This design works by minimizing the "troublemaker" downward deflection that can precipitate wing-tip stall and by increasing aileron drag on the descending wing to help equalize drag and minimize adverse yaw.
Slotted differential ailerons improve airflow and effectiveness at high angles of attack, while Frise ailerons offer an alternative method to minimize adverse yaw by creating additional drag on the upward-deflecting aileron.

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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.