What Are Ailerons? How They Roll a Plane, and Why They Need the Rudder

Ailerons are the hinged panels on the back edge of each wing, out near the tips. They control roll: turn the control wheel to the right and the right aileron rises while the left one drops, so the left wing gains lift, the right wing loses some, and the airplane rolls to the right.

Rolling is how an airplane starts every turn, because banking tilts the wing’s lift toward the inside of the turn. That makes the ailerons one of the three primary flight controls, alongside the elevator and the rudder.

They also come with a built-in flaw called adverse yaw, which is why the rudder has to help. Below: how ailerons work, how they differ from flaps, how airliners and bombers handle roll, and how the aileron ended up at the heart of the Wright brothers’ patent war.

Ailerons at a Glance

Question	Answer
What are they?	Hinged panels on the outboard trailing edge of each wing
What do they control?	Roll, around the longitudinal axis that runs from nose to tail
How do they move?	In opposite directions: one goes up while the other goes down
What moves them?	The control wheel, stick or side stick, through cables, pulleys and push-pull tubes on light airplanes and hydraulics on jets
Control wheel to the right	Right aileron up, left aileron down, airplane rolls right
Main side effect	Adverse yaw, which the pilot cancels with rudder
Primary or secondary control?	Primary, with the elevator and rudder
Common variations	Differential and Frise-type ailerons, flaperons, and spoilers that assist or replace them

How Ailerons Work

The FAA describes ailerons as attached to the outboard trailing edge of each wing, moving in opposite directions from each other. Tilting one up and the other down changes the shape of each wing’s outer section.

An aileron that deflects down increases the camber, or curve, of that part of the wing, so the wing makes more lift. An aileron that deflects up decreases the camber, so that wing makes less. The difference in lift between the two wings rolls the airplane.

You can also picture it through the angle of attack, the angle between the wing and the oncoming air. Lowering an aileron raises the angle of attack of that part of the wing, which is why it lifts, and also why it drags, as the adverse yaw section below explains.

Ailerons sit near the tips for leverage. NASA’s Glenn Research Center describes them as small hinged sections on the outboard portion of the wing, and a lift change that far from the fuselage has a long lever arm, so a small surface produces a strong rolling force.

On a light airplane, cables, bellcranks, pulleys or push-pull tubes connect the ailerons to the control wheel or stick. Airliners add hydraulic power, covered further down.

Which way do the ailerons move?

Turn the control wheel, or push the stick, to the right and the right aileron goes up while the left aileron goes down. The right wing drops and the airplane rolls right. Turn it left and everything reverses.

The FAA’s Airplane Flying Handbook describes it from the seat: right pressure on the aileron control makes the right wing bank lower in relation to the pilot. The same handbook tells pilots to hold the controls lightly with the fingers, not grab them with a closed hand, so they can feel the airplane.

On most airplanes the ailerons and the elevator share one control: turning the wheel rolls the airplane, and pushing or pulling it pitches the nose. Some airplanes use a control stick or a side stick instead of a wheel, and it works the same way.

Ailerons and the Three Axes of Flight

An airplane rotates around three axes, and each has its own primary control. The FAA counts the ailerons, the elevator and the rudder as the primary controls required to control an aircraft safely in flight.

• Roll around the longitudinal axis, nose to tail: controlled by the ailerons.
• Pitch around the lateral axis, wingtip to wingtip: controlled by the elevator.
• Yaw around the vertical axis, top to bottom: controlled by the rudder.

Everything else is a secondary control. Flaps, leading-edge devices, spoilers and trim improve performance or relieve the pilot of heavy control forces, the FAA says, but they are not the controls it counts as required to fly safely.

How Ailerons Turn the Airplane

An airplane does not steer like a car or a boat. It turns by banking: tilt the wings and part of their lift points toward the inside of the turn, and the FAA says that horizontal component of lift is what moves the airplane toward the banked direction.

That makes the ailerons the controls that start every turn. The Airplane Flying Handbook puts it simply: the ailerons bank the wings and determine the rate of turn for a given airspeed. Our guide to how airplanes turn covers the rest of the physics.

Because a banked wing spends some of its lift on turning, the pilot adds back pressure on the elevator to hold altitude. The steeper the turn, the more back pressure it takes.

Once the bank is set, what the pilot does with the ailerons depends on how steep it is. The FAA splits turns into three classes:

• Shallow, about 20° or less: the airplane’s stability slowly levels the wings, so the pilot holds a little aileron into the turn.
• Medium, about 20° to 45°: the airplane holds its bank on its own, and the ailerons go back to neutral.
• Steep, about 45° or more: the airplane tends to keep rolling, so the pilot holds a little opposite aileron to stop it overbanking.

The overbanking comes from the wings themselves. In a turn the outside wing travels a longer path in the same time, so it flies faster and makes more lift than the inside wing.

Adverse Yaw: Why Ailerons Need the Rudder

Here is the catch. The wing with the lowered aileron makes more lift, and more lift always brings more induced drag.

The FAA explains that the extra drag slows that rising wing slightly and yaws the nose toward it, which from the pilot’s seat is the opposite direction of the bank. Roll right and the nose swings left. This is adverse yaw.

It is worst at low airspeed, at high angles of attack, with large aileron deflections, and on airplanes with long wingspans. Slow flight makes it worse twice over, because the pilot needs bigger aileron inputs and the rudder is less effective at the same time.

The fix is rudder in the same direction as the roll, applied together with the aileron. Pilots call the result a coordinated turn, and the ball on the turn coordinator stays centered when they get it right.

Once the bank is established, aileron and rudder pressure are relaxed together, and the roll-out works the same way in reverse.

Types of Ailerons

The FAA’s handbook describes four common aileron arrangements. Three of them exist mainly to shrink adverse yaw, and none removes it completely, so pilots still coordinate with rudder.

Differential ailerons

The up aileron travels farther than the down aileron for the same movement of the wheel. That adds drag on the descending wing to offset the drag on the rising one, reducing adverse yaw without eliminating it.

Limiting how far the down aileron moves also lowers the risk of stalling that wingtip at high angles of attack. The de Havilland Tiger Moth biplane is one of the best-known early examples.

Frise-type ailerons

Named for Leslie Frise of the Bristol Aeroplane Company, this aileron pivots on an offset hinge. When it rises, its leading edge pokes down into the airflow under the wing and creates drag that helps balance the lowered aileron on the other side.

The FAA notes that the design also forms a slot that keeps air flowing smoothly over the lowered aileron, making it more effective at high angles of attack. Frise developed it in the 1930s to lighten stick forces, and the 1938 Piper J-3 Cub helped bring it to a wide audience.

Coupled ailerons and rudder

Interconnect springs move the rudder automatically whenever the ailerons move. Roll left and a cable and spring pull the left rudder pedal forward just enough to stop the nose yawing right.

The pilot can override the springs when a deliberate slip is needed.

Flaperons

Flaperons are one set of surfaces that does both jobs. They move in opposite directions to roll the airplane like ailerons, and droop together to work as flaps.

The pilot keeps separate aileron and flap controls, and a mixer combines the two inputs. The FAA’s example is the Skystar Kitfox MK 7, and it notes that many designs mount the surfaces slightly away from the wing for clean airflow at high angles of attack and low airspeeds.

Ailerons vs Flaps

They sit side by side on the trailing edge and look alike, which is why so many people mix them up. The difference is how they move: ailerons move in opposite directions to roll the airplane, and flaps move together on both wings.

	Ailerons	Flaps
Where	Outboard trailing edge, near the tips	Trailing edge, inboard of the ailerons
How they move	Opposite directions, one up and one down	Same direction, down together
What they do	Roll the airplane	Add lift and drag at a given angle of attack
When they are used	Constantly, whenever the pilot moves the wheel or stick	Extended for takeoff, approach and landing, retracted for cruise
Type of control	Primary, required to fly safely	Secondary, improves performance

The FAA calls flaps the most common high-lift device on aircraft. They increase both lift and induced drag at any given angle of attack, which lets an airplane cruise fast and still land slowly.

The two jobs meet in the flaperon described above. On jets, the ailerons and flaps also compete for the same limited stretch of trailing edge, which shapes how big airplanes roll.

Ailerons on Airliners and Jets

A jet’s ailerons are smaller than you might expect. The FAA explains that jet transports need as much of the trailing edge as possible for flaps, and that a conventional-size aileron would twist the wing at high speed.

So jets share the job with spoilers, panels on top of the wing that rise to spoil lift. When the pilot rolls, the spoiler on the side of the up-going aileron extends and helps that wing drop. Our guide to how airplane spoilers work covers their other jobs.

Some jet transports carry two pairs of ailerons: outboard low-speed ailerons and inboard high-speed ones. The FAA says the outboard pair locks in the faired position once the flaps are fully retracted after takeoff, leaving the inboard pair and the spoilers to roll the airplane at speed.

Ailerons on the Boeing 737

The 737’s ailerons are powered by hydraulic systems A and B, according to the pilot reference site b737.org.uk. If both systems fail, the pilots can still move the ailerons manually from the control wheels, and flight spoilers augment them in normal flight.

Full aileron travel is about 20°, which takes about 82° of control wheel rotation. By design, the autopilot can command only about 4.5° of aileron.

There is a backup for a jam, too. If the aileron system jams, the co-pilot’s wheel can still move the spoilers hydraulically.

Aileron reversal

At high speed, a deflected aileron can twist a thin, flexible wing enough to undo its own effect. The FAA lists aileron reversal among the control problems that an airplane’s maximum operating speed limits are there to prevent.

Ailerons Near a Stall and in a Spin

Designers want the ailerons to keep working as long as possible when the wing stalls. Most straight-wing airplanes are built so the wing root stalls before the tip, often by twisting the wing slightly, which keeps the ailerons effective out at the tips.

That does not make them safe to use at the stall. If the airplane rolls left as it stalls and the pilot applies right aileron, the lowered left aileron raises that wingtip’s angle of attack and can stall it completely, rolling the airplane further left.

In a spin, the FAA recovery procedure puts the ailerons in neutral. Aileron with the spin can speed up the rotation, and aileron against it can flatten the spin and delay recovery, or even make it unrecoverable.

Our guide to the flat spin covers the most dangerous version.

Aileron Trim and Balance

Holding steady aileron pressure is tiring, so many airplanes have aileron trim. Nearly all light airplanes have elevator trim, but the FAA says flight-deck trim for the rudder and ailerons tends to arrive as airplanes gain power, weight and complexity.

Where all three axes can be trimmed, the handbook’s order is rudder first, then elevator, then aileron.

On the 737, aileron trim moves the neutral point of the feel and centering mechanism. Using it with the autopilot engaged is prohibited, because the airplane can roll sharply when the autopilot disconnects.

Big control surfaces can be heavy to move, so designers add aerodynamic help. Balance tabs move opposite to the surface they are attached to and lighten the load, and the 737’s ailerons carry balance tabs and balance panels.

Aerobatic airplanes often use spades instead: flat plates mounted on an arm ahead of the aileron hinge that reduce the force the pilot needs to deflect it.

Who Invented the Aileron?

The Wright brothers did not use ailerons. The 1903 Wright Flyer’s pilot lay on the lower wing and moved a hip cradle that pulled wires to warp the wings and turn the rudder at the same time.

The aileron itself traces back to the British scientist Matthew Piers Watt Boulton, who described it in an 1864 paper and patented it in 1868. His patent was forgotten, and the idea was reinvented in France decades later.

Ailerons won because they worked better. They proved more effective than wing warping and did not weaken the wing structure, and by 1911 most biplanes used them.

By 1915 they were almost universal on monoplanes too, and the Wright company quietly switched from wing warping to ailerons around the time of the patent pool.

Where does the word “aileron” come from?

Aileron is French for little wing. Merriam-Webster traces it to the Middle French aleron, the tip of a bird’s wing, built on aile, meaning wing.

According to the dictionary, its first print use for a roll-control surface was probably in the French journal L’Aérophile on July 1, 1908, in a description of Louis Blériot’s Blériot VIII. Before that, ailerons were often called horizontal rudders.

Can a Plane Fly Without Ailerons?

Yes. Every airplane needs a way to control roll, but ailerons are only one way to get it.

The Mitsubishi MU-2 turboprop rolls with spoilers on top of the wing instead of conventional ailerons. That frees the trailing edge for full-span, double-slotted flaps, which give it a high cruise speed and a low landing speed.

The B-52 Stratofortress went the same way for a different reason. Its thin wing twisted when the ailerons moved, undermining roll control, so spoilers did most of the rolling from the start.

Early B-52s kept small “feeler” ailerons to give the pilots feedback through the controls. The late B-52G eliminated them altogether, and the lack of ailerons is part of why the G and H models were more prone to Dutch roll.

Other designs skip ailerons too. Delta-wing aircraft combine ailerons and elevators into elevons, and some fighters roll with tail surfaces that move independently, called tailerons. Weight-shift aircraft roll by moving a control bar, much like a hang glider.

Even the rudder can roll an airplane. The FAA warns that too much rudder in a turn gives the outside wing extra lift and banks the airplane toward the rudder, which is the setup for a cross-control stall.

For nearly every airplane flying today, though, two small panels near the wingtips do the job, as they have on almost every monoplane since about 1915.

FAQ

What are ailerons on a plane?

Ailerons are hinged panels on the outboard trailing edge of each wing, near the wingtips. They are one of the three primary flight controls, alongside the elevator and the rudder, and they control roll, the rotation around the axis that runs from nose to tail.

What is the function of an aileron?

An aileron rolls the airplane by changing how much lift each wing makes. The lowered aileron adds lift to its wing and the raised aileron reduces lift on the other, so the airplane banks, and banking is how an airplane turns.

What's the difference between flaps and ailerons?

Ailerons move in opposite directions to roll the airplane and are used constantly in flight. Flaps move down together on both wings to add lift and drag for takeoff and landing, and they are a secondary control that the pilot extends when needed and retracts for cruise.

Which way do the ailerons move when you turn right?

Turning the control wheel or moving the stick to the right raises the right aileron and lowers the left one. The left wing gains lift, the right wing loses some, and the airplane rolls to the right.

Can you fly a plane without ailerons?

Yes. The Mitsubishi MU-2 rolls with spoilers instead of conventional ailerons, the late B-52G eliminated its ailerons, and the Wright Flyer used wing warping. Delta-wing aircraft use elevons, some fighters use tailerons, and weight-shift aircraft roll by moving a control bar.

What is adverse yaw?

Adverse yaw is the tendency of the nose to swing away from the direction of a roll. The lowered aileron creates extra lift and extra drag on the rising wing, which pulls the nose the other way, and pilots cancel it with rudder in the direction of the turn.

What are flaperons?

Flaperons are control surfaces that work as both flaps and ailerons. They move in opposite directions to roll the airplane and droop together to act as flaps, with a mixer combining the pilot’s separate aileron and flap inputs.

How do the ailerons work on a Boeing 737?

The 737’s ailerons are hydraulically powered, with manual reversion from the control wheels if both hydraulic systems fail. Flight spoilers on top of the wing rise with the ailerons to add roll control, and full aileron travel is about 20 degrees.

Why is it called an aileron?

Aileron is French for little wing. The word goes back to the Middle French word for the tip of a bird’s wing, and its first print use for an airplane’s roll-control surface was probably in the French journal L’Aérophile in July 1908.