An aileron - French for ‘little wing’ -is a hinged control surface set into the outboard trailing edge of each wing. Working as a pair, these surfaces are the aircraft's primary means of commanding roll about its longitudinal axis: one aileron rises to reduce lift while the other descends to increase lift, tilting the lift vector and banking the airframe left or right.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What are ailerons in aviation?
Ailerons are a primary flight control surface, which are attached to the outboard trailing edge of each wing and are controllable. An aileron is a hinged flight control surface that forms part of the trailing edge, and ailerons are used in pairs to control roll. Roll is movement about the longitudinal axis of an aircraft which results in tilting of the lift vector. Ailerons are hinge-like flaps on the trailing edge. When one aileron rises and the other drops, the opposing movement creates a rolling motion around the longitudinal axis that extends from nose to tail.
What is the main purpose of ailerons on an aircraft?
The primary function of ailerons is to facilitate the rolling movement of an aircraft. Ailerons are used in pairs to control aircraft roll. When one aileron's trailing edge goes up the opposite one goes down, creating differential lift that generates rolling motion around the longitudinal axis. This roll banks the aircraft left or right so that the tilted lift vector changes the flight path, allowing the pilot to begin and hold a turn.
Why are ailerons important?
Ailerons are important for flight safety and maneuverability. They keep the aircraft stable and maneuverable during every phase of flight. By letting the pilot tilt the wings, ailerons change the aircraft's flight path and allow smooth entry and exit from turns. Without them, precise roll control is impossible.
Ailerons are necessary for coordinated turns with the rudder. When aileron input creates adverse yaw, opposite rudder is required to correct adverse yaw. This pairing keeps the nose aligned with the direction of flight, preventing slip or skid and protecting flight safety.
Ailerons are vital for maintaining stability during a spin. Pilots can use ailerons to maintain stability during a spin by carefully managing lift on each wing. By limiting the angle of bank and stopping over-rotation, ailerons help the pilot recover quickly and safely.
Where are the ailerons located on an aircraft?
Ailerons are typically located near the wingtips and form part of the trailing edge of each wing. Each aileron is attached by a hinge positioned near its front edge, allowing the surface to pivot upward or downward. In large aircraft, two ailerons are mounted on each wing: one set near the tip in the conventional position, and another set approximately mid-wing, immediately outboard of the inboard flaps. Modern airliners carry a second pair of ailerons on their wings.
What are the types of aircraft ailerons?
The types of aircraft ailerons are outlined below.
- Differential Ailerons: With differential ailerons, one aileron is raised a greater distance than the other. This produces an increase in drag on the descending wing.
- Frise-Type Ailerons: In frise-type ailerons, the aileron that is being raised pivots on an offset hinge. This projects the leading edge of the aileron into the airflow and creates drag. It helps equalize the drag created by the lowered aileron on the opposite wing and reduces adverse yaw.
- Coupled Ailerons and Rudder: Coupled ailerons and rudder are linked controls. This is accomplished with rudder-aileron interconnect springs, which help correct for aileron drag by automatically deflecting the rudder at the same time the ailerons are deflected.
- Flaperons: Flaperons combine both aspects of flaps and ailerons. In addition to controlling the bank angle of an aircraft like conventional ailerons, flaperons can be lowered together to function much the same as a dedicated set of flaps.
Do jets have ailerons?
Only some jets have ailerons. The F-4 Phantom II carries very small conventional ailerons at the wing-tips, but at higher speed the outboard aileron is locked and roll control is provided by the differential horizontal stabilizer deflection. The F-14 does not have ailerons on the wings. Instead, its tail control surfaces - known as rolling tails - handle roll. Several modern fighter aircraft have no ailerons on their wings and employ spoilerons, surfaces that are extended on the wing or fuselage to disrupt the airflow and create the needed rolling moment.
How do ailerons work?
Ailerons work by altering the effective shape of the airfoil of the outer portion of the wing, altering lift on each side through upward or downward deflection. Aircraft roll is produced by differential lift on the wings. When you turn the control wheel to the left, the left side goes up and the right side goes down, creating the banking motion that curves the flight path.
They are controlled via cables and bellcrank: the bellcrank converts movement from cable to metal rod, articulating the aileron. A spade produces a downward aerodynamic force on an upward-deflected aileron, helping rotate the assembly so the aileron deflects further upward. By deflecting airflow at the wing's trailing edge, ailerons adjust the angle of attack: increasing it on the down-going wing and decreasing it on the up-going wing, thus generating more lift on one side and less on the other. This differential lift, working in opposition, changes the airplane's attitude and initiates a coordinated turn when combined with rudder input. Differential ailerons solve adverse yaw - the tendency of the nose to yaw opposite to the roll.
Which way do ailerons move?
Ailerons move in opposite directions from one another. Rotating the control wheel right moves the right aileron up and the left aileron down, making the right wing drop and the aircraft roll into a right turn; rotating left gives the mirrored motion that lowers the left wing.
To complete a full left roll the pilot continues to hold the wheel left, keeping the left aileron deflected upward and the right aileron downward until the desired bank angle is reached. When the stick returns to neutral, the ailerons again move in opposite directions to cancel lift difference and hold the bank steady.
What is the role of the aileron during takeoff?
During take-off, ailerons are pivotal for lateral control. They counter cross-wind by enabling the pilot to apply pressure into the wind, keeping the wings level and the nose pointed down the runway centerline. Ailerons are used during take-off roll to achieve a smooth takeoff, and the right combination of aileron and rudder gives a perfectly smooth takeoff roll.
At low speed during takeoff, both ailerons on each wing are active. Pilots make large aileron deflections at low speed, and airflow over control surfaces is reduced. Outboard ailerons become active whenever the flaps are extended beyond the fixed setting, aiding control while flaps enhance lift at lower speeds during takeoff and landing.
As the aircraft accelerates, the pilot reduces aileron input to keep wings level. At higher speed, the outboard aileron is locked and only the inboard aileron is functional. As flaps are retracted, the outboard aileron control system is locked out, leaving spoilers to assist: spoilers are used during takeoff in case of a crosswind, and spoiler deployment creates a rolling moment that helps counteract adverse yaw. During landing, the sequence reverses: flaps extend again, the outboard ailerons re-engage, and both ailerons resume activity for slow-flight operations, allowing precise roll control until the aircraft is safely on the ground.
What causes aileron oscillation?
Aileron oscillation is mostly caused by low tension in aileron cables. Slack or low tension in aileron cables makes the aileron prone to flutter. Missing bushings, misaligned brackets, and weak connections between aileron and wing cause flutter. Excessive free play in the controls puts the aileron at the mercy of aerodynamic forces. High speed and transonic speeds cause aileron flutter and buzz. Aileron oscillations develop into divergent flutters, causing severe damage to the structure.
Material fatigue is the primary cause of aileron failures. Repeated stress cycles cause microscopic cracks in the aileron's structure, and these cracks propagate, compromising the integrity of the aileron. Environmental conditions exacerbate fatigue. Corrosion is another cause of aileron failures as it weakens the structural integrity of the aileron, making it more susceptible to flutter.
Overloading the aircraft induces excessive stress on the ailerons, leading to deformation or failure. Improper maintenance or incorrectly rigged cables cause reversed control, as happened in the Piper PA-22 crash. Reports from Hawker 800XP and 850XP operators show wing/aileron oscillations above 33,000 ft (10,058 m), indicating altitude and speed as external factors.
What is the history of the aileron?
The idea of the aileron was patented in 1868 by British scientist Matthew Piers Watt Boulton, yet the concept lay dormant until French engineer Robert Esnault-Pelterie constructed gliders and powered aircraft with rigid, hinged control surfaces in 1904, creating what historians call the first true ailerons. These surfaces quickly drew attention: in 1908 Glenn Curtiss began using similar hinged surfaces, an action that triggered a celebrated legal battle with the Wright brothers, who had promised to sue anyone anywhere who flew with anything remotely resembling wing-warping. The decisive stylistic breakthrough came when Henry Farman attached ailerons to rectangular slots on his 1909 Farman III. Those surfaces were the first to resemble the ailerons on modern aircraft, performing spectacularly and allowing solidly built wings to replace the flexible geometries of earlier control schemes.
By 1911 most biplanes were built using ailerons, and by 1915 the devices had become commonplace on monoplanes as well. Throughout the years ailerons have appeared in different forms, evolving from simple mechanical linkages to high-tech fly-by-wire systems that incorporate cutting-edge materials and sophisticated control systems. In the judgment of historian C. H. Gibbs-Smith, the aileron remains one of the most remarkable inventions in aeronautical history, and it continues to evolve with aviation.
