Do you know the difference between differential and symmetrical ailerons? Most fixed-wing aircraft have ailerons. Consisting of hinged flat-like surfaces on the wings, they are used to control rolling and banking. Some airplanes, however, have differential ailerons, whereas others have symmetrical ailerons.
The Basics of Ailerons
Ailerons are flight control surfaces found on the trailing edge of an airplane’s wings. Pilots can raise or lower them to control rolling and banking.
Ailerons move in opposite directions, which causes the airplane to turn. When raised, the respective aileron — known as an upward-deflected aileron — will reduce the amount of lift generated by the wing. The aileron on the opposite wing — known as a downward-deflected aileron — will simultaneously drop.
What Are Symmetrical Ailerons?
Symmetrical ailerons are the most common type. They are characterized by a synchronous, static angle. In other words, both ailerons move at the same angle. If the aileron on the right wing moves upward by 20 degrees, the aileron on the left wing will also move by 20 degrees. Symmetrical ailerons still move in opposite directions, so the downward-deflected aileron will simply move down by 20 degrees.
What Are Differential Ailerons?
Differential ailerons are designed to move at different angles. Like their symmetrical ailerons, they move in opposite directions. The difference is that pairs of symmetrical ailerons always move at the same angle, whereas pairs of differential ailerons move at different angles.
A differential aileron on the right wing may move upward by 20 degrees, whereas the differential aileron on the same airplane’s left wing may move downward by 15 degrees. Movement angles for differential ailerons can vary depending on the aircraft. With that said, upward-deflecting differential ailerons always have a higher movement angle than the downward-deflecting differential ailerons with which they are paired.
Why Some Airplanes Use Differential Ailerons
The main reason some airplanes use differential ailerons is to counter adverse yaw. Differential ailerons are characterized by different movement angles. As previously mentioned, the upward-deflecting differential aileron has a higher movement angle than the downward-deflecting differential aileron. This means the downward-deflecting differential aileron will produce less lift and drag.
Using the differential ailerons, pilots can roll the airplane more smoothly. There’s less adverse yaw, resulting in smoother turns and fewer rudder corrections needed. Differential ailerons still provide a means for controlling rolling and banking, but they produce less adverse yaw.
