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

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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.

In this article, we’ll go over 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 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 FlightMovement NameAssociated Primary Flight Control
Longitudinal AxisRollAilerons
Lateral AxisPitchElevator
Vertical AxisYawRudder

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. 

Commercial Airline Aileron

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?

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.

Piper Archer Aileron

Adverse Yaw

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

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 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.

Commercial Aileron Gif

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. 

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.

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Comments

3 responses to “Ailerons – What are They, and How do They Work?”

  1. Christopher K.

    I really like this discussion, but I think there is more to your quote, “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.”

    It’s not necessarily wrong, but ailerons and rudders are not what pulls the plane through the turn. Yes, the aileron rolls the airplane and the rudder is used to bring the nose back in line with relative wind, but it’s the elevator that gives us that horizontal component of lift (or centripetal force), and pulls us through the turn. Without an increase in A.O.A. by use of our elevators, all the airplane would do is roll into the direction of the turn we’ve told it to and begin to descend. We have to create the additional lift needed to maintain level altitude and we do so by increasing our A.O.A., which is back pressure on the elevator.

    My DPE for my CFI checkride and I had a really great discussion about this. I think many student pilots and newly certificated private pilots have a poor understanding of the aerodynamics of a turn. Just thought I’d share my two sense 🙂

    There aren’t many articles or videos that really dive into the aerodynamics of a turn, though, so I really appreciate the input you’ve offered.

  2. Lawrence McCall

    This article was very helpful in understanding the increase and decrease in the angle of attack with the up or down ailerons. As a student pilot, I’m trying to fulling understand why a wing deflected down with an up aileron will stall in a skidded turn which can lead to a spin. I understand that as the angle of attack increases, you come closer to a stall. But if the up aileron decreases the angle of attack, why does the lowered wing lead to a stall in a skid? I know the relative wind over the fuselage in a skid plays a part but not sure if there’s more. Thanks.

    1. Brian Brassaw

      So the first thing we have to understand is what are the exact conditions in a skidding turn. Let’s look at this scenario, we’re in a left turn from base to final: to start, our left wing will be dipped downwards and our left aileron deflected UP. Once established in the turn our ailerons go NEUTRAL. If this were to be a skidding turn, we would be using too much left rudder, bringing the nose to the inside of the curve. This does a couple things, first it increases our aircrafts overbanking tendency and rolls us further left, and second we want to incorrectly fix this with right aileron rather than decreased rudder pressure. With this left rudder, right aileron combination we could now potentially spin if we stall the aircraft because the wings will stall unevenly.

      This skid itself doesn’t induce a spin, the spin comes from incorrect control inputs to correct the attitude of the airplane and the direction of the nose. To be in a continuous skidding turn, the lower wing would have aileron deflected DOWN because we’re trying to fix something with the wrong controls, and the downward deflected wing will have a higher angle of attack and would stall first.

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