Ailerons – What are They, and How do They Work?

Ailerons are one of the main controls you use to fly the plane, so it’s important to understand how ailerons work.

This is also one of those times when understanding a little bit of aerodynamics will make you a better pilot in the cockpit.

As a private pilot student, your instructor will go in depth in teaching you how they function and how to properly manipulate them to control the aircraft.

In this article, we’ll go over what do ailerons do, the aerodynamics of ailerons and go through a few different types of ailerons and alternatives. After you read this be sure to learn about the rest of the airplane in our guide to airplane parts.

What are Ailerons?

Ailerons are hinged flight control surfaces attached to the trailing edge of an airplane’s wings. They are used to control the aircraft’s roll and help it turn.

Ailerons are one of the three primary flight controls found on an airplane. That means they are fundamental in controlling the plane around one of the three axes of flight. 

For a quick review, movement around each of the three axes of flight has a name, and each type of movement is controlled by its own control surface. 

Axis of Flight	Movement Name	Associated Primary Flight Control
Longitudinal Axis	Roll	Ailerons
Lateral Axis	Pitch	Elevator
Vertical Axis	Yaw	Rudder

Ailerons are mounted on the outboard trailing edge of the wings. When one aileron is deflected upward, the opposite side goes downward.

They are controlled by turning the yoke or stick left or right in the cockpit. When you turn left, the left aileron goes up, and the right goes down. When you roll right, the opposite happens. 

It’s important to remember that ailerons alone do not turn an aircraft. All ailerons do is roll the plane left or right. Therefore, you will also need rudder inputs to turn the plane. 

Unlike a car on the road, no force immediately rolls a plane back to straight and level when you are done.

Instead, you apply aileron to roll into a turn, keep the wheel neutral throughout the turn, and then roll the plane back to level using an opposite-direction roll when you finish. 

How Do Ailerons Work?

So, now you know what ailerons do, but how do they do it? The answer comes to us by way of some intricate aerodynamics.

To dive into what makes ailerons work, you’ll need to review the fundamentals of wings and how they make lift. Here’s a quick recap.

• Wings make lift thanks to Bernoulli’s Principle. The air flowing over the top of the wing travels faster, producing less pressure than the air flowing below the wing. The pressure difference between the top and bottom results in lift on the wing.
• A wing can make more lift by increasing its angle of attack. The angle of attack is the angle between the relative wind and the wing’s chord line. 
• A pilot can increase the angle of attack by either pulling up or altering the wing’s shape. Flaps work by changing the wing’s shape–they move the chord line to increase the angle of attack and make more lift. 

How does this apply to ailerons? Ailerons work the same way that flaps do–by changing the shape of the wing and moving the chord line. When an aileron is deflected down, it increases the angle of attack on that part of the wing. This wing will make more lift, so it will start going up.

At the same time, the aileron on the other wing deflects upward. This also changes the chord line, but in the opposite way. It reduces the angle of attack, meaning that part of the wing is now making less lift—that part of the wing drops.

Of course, the two wings are attached together, with the fuselage in the middle. When the ailerons are deflected, the plane starts rolling in the direction of the upward aileron.

Adverse Yaw

You might also remember from aerodynamics that when you make more lift, you also make more drag. 

Induced drag is a byproduct of lift. As you increase the angle of attack on a wing, more and more induced drag is made. This is why you must add more power to maintain your altitude during slow flight. 

When your aileron goes down to increase the angle of attack and make more lift, it will also cause an increase in the induced drag on that part of the wing. Remember, this is the wing that goes up as you roll the plane. The induced drag will pull that part of the wing-back, introducing a yawing motion to the plane. 

It’s called adverse yaw because the force is pulling you away from the direction you want to turn. If you relied only on your ailerons, they would roll you in the direction you want to turn but yaw you away from it. This is one of the big reasons that you need to use the rudder to help you turn.

One of the main purposes of the rudder is to counteract the adverse yaw created by the airplane ailerons.

Aircraft designers are pretty clever, so you might not notice a lot of adverse yaw when you fly your trainer. They can minimize it in several ways, but these generally work best at cruise airspeeds and normal maneuvers. Adverse yaw is at its worst when flying slowly and using large control surface deflections.

Types and Designs of Ailerons

Here’s a look at the types of ailerons you’ll find on planes. Most of these designs are ways engineers can tinker with the amount of adverse yaw. But none of these designs eliminate adverse yaw. So you’ll always have to use some rudder inputs.

Differential Ailerons

The idea behind differential ailerons is pretty simple–make the raised aileron go up more than the lowered aileron goes down.

That way, the raised aileron will create extra drag on the descending wing, which counters the adverse yaw made by the lowered aileron. Using the ailerons still results in drag, but it balances out enough that the adverse yaw isn’t so adverse.

Frise-Type Ailerons

Frise ailerons pivot on an offset hinge so that the upward deflecting aileron also projects below the wing. This has the same net result as the differential ailerons–drag is increased on the lowered wing enough to counter the drag made by the raised wing.

Some frise-type ailerons also create a slot for air to pass over them when they are lowered. This makes the lowered aileron very effective at high angles of attack and low-speed flying. 

Coupled Ailerons

Coupled ailerons are designed to move the rudder and the ailerons when you move the controls. It’s accomplished with a simple set of springs between the yoke and rudder pedals. The pilot can override the couple if they need to perform a slip. 

There were a few models of planes that did not have rudder pedals at all and relied on coupled ailerons for all maneuvers. The most notable of these was the Ercoupe. 

Flaperons

Flaperons are combination flaps and ailerons. They are controlled in the same way as a plane with separate controls. These are common on low-speed aircraft like bush planes.

They’re often mounted away from the wing to get undisturbed airflow during high angle of attack operations.

Elevons

Elevons (sometimes called tailerons) combine the elevator and aileron. You will typically see these used on delta wing designs or fighter jets. They are on the trailing edge of the wing.

Spoilerons

Spoilerons are positioned on the outside portion of each wing to spoil the lift on that side causing the wing to drop. Only one side deploys at a time. Spoilerons can be used in conjunction with ailerons or they can replace them entirely. See the Mitsubishi MU-2 for an example of an aircraft that uses them.

You can read all about ailerons in Chapter 6: Flight Controls from the FAA’s Pilot’s Handbook of Aeronautical Knowledge.