Steering an Aircraft: Use Ailerons for Lateral Control in Planes


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The aileron can clearly be seen at the trailing edge of the wingtip. Photo Credit: Yawar Saeed

What are ailerons, anyway? These flat hinged flaps are critical for steering a plane to the left or right.

If a pilot wants the airplane to turn, he or she must first roll over its longitudinal axis at a certain bank angle. Ailerons provide the control over the tendency of the plane to roll. The rectangular flaps are installed at the outer trailing edge of each wing, and operate opposite to one another; if the right aileron moves down, the left one moves upwards.

Ailerons – Principle of Operation

Technically, an airplane’s wing “flaps” are a completely different structure, and are located inboard the wing (near the wing root) on its trailing edge. The aileron, looks like a flap too, but fulfills a completely different function – Simply put, these flap-like structures work to turn the plane by creating more lift on one wing while decreasing the lift generated by the other. The down-going aileron increases the overall camber of the wing exposed to the relative airflow. This, in turn, results in that wing generating more lift. Consequently,  the wing moves upwards.

The up-going aileron decreases the overall angle of the wing thereby resulting in a reduction of lift produced from that wing. As a consequence, this wing drops down.

With one wing rising upwards while the other dropping downwards, we now have a turning moment that rolls the airplane in the direction of the dropping wing. Two key points in this regard:

  • The aileron of the rising wing will always move downwards (increased lift).
  • The aileron of the falling wing will always move upwards (reduced lift).

Pilot Control on Ailerons – Systems Working Behind the Scene

The Control Column of a Cessna-150. Photo Credit: Junaid Ali

Pilots control the movement of  the airplane’s ailerons through the control column, which is connected to the ailerons via hydraulic lines (light aircraft such as the Cessna-150 may have a mechanical linkage). When the pilot turns the control column to the right, the right aileron moves upward to reduce the lifting capability of the right wing. Airbus aircraft have a side stick instead of the conventional control column for flight control.

Adverse Aileron Yaw

Ailerons are part of an aerodynamic wing design, and like all lift-producing surfaces, have a certain amount of drag produced as a by-product. This produced drag is greater on the rising wing (aileron down) than that at the falling wing (aileron up) and is commonly known as induced drag, which is primarily associated with the production of lift.

This results in a slower motion of the rising wing thus resulting in a yaw opposite the direction of turn; adverse aileron yaw. Hence, a side effect of rolling an airplane is its tendency to yaw. This can, however, be corrected by introducing design modifications in the ailerons such as differential ailerons, frise-type ailerons and aileron-rudder coupling.

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