Ailerons are the primary flight control surfaces used to roll an aircraft: a hinged flight control surface attached to the trailing edge of each wing, they are used in pairs to bank the aircraft. Working in opposite directions - when one aileron moves up the other moves down - they create a rolling motion around the longitudinal axis. To reduce adverse yaw, different types of ailerons like differential, frise, and coupled systems are employed, while advanced designs like flaperons, spoilerons, and elevons combine aileron function with other control surfaces.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What do ailerons control?
Ailerons control the aircraft's roll about the longitudinal axis. Ailerons are located on the trailing edge of each wing, near the outboard section. They are primary control surfaces which control the rolling motion of the aircraft by adjusting the lift on each wing. Ailerons are used in pairs, with one aileron moving up while the other moves down. This roll normally results in a change in flight path and helps the aircraft turn. Ailerons control movement about the longitudinal axis, producing bank.
Using ailerons during landing is necessary. Ailerons deflect upward to reduce camber and hold drift during crosswind landing and pilots can control the aircraft's roll to stay aligned.Ailerons control roll which results in banking, and the rudder counters adverse yaw created by that roll. Ailerons are replaced by spoilerons in large jets like the 737.
What do ailerons control regarding the wing? Ailerons control roll by varying lift distribution across the wing, with spoilerons assisting or replacing them in large jets such as 737.
Aileron movement creates a differential in elevation which is utilized by the wings. I learned that one aileron deflects while the other deflects down. Their main purpose is to control the aircraft’s rotation about the longitudinal axis.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
What controls the ailerons?
Control yokes are used to control the ailerons on an airplane. Ailerons can be moved by rotating the yoke left or right. Turning the yoke to the left causes the left aileron to go up and the right aileron to go down. The pilot uses the yoke to control the airplane's roll. In more modern aircraft, inputs are first sent to a fly-by-wire system, which then sends a corresponding signal to actuators attached to aileron booster systems and control surfaces. Human muscle power alone is not enough for larger aircraft, so hydraulic systems are used, in which yoke movements control hydraulic valves and actuators.
The pilot controls the aircraft's roll by turning the control yoke or sidestick. Ailerons are connected to the control yoke by cables, pulleys and bellcranks. Turning the yoke to the left increases lift on the right wing and decreases lift on the left wing, causing the airplane to bank left. Turning the yoke to the right increases lift on the left wing and decreases lift on the right wing, causing the airplane to bank right. A level turn is accomplished by applying coordinated aileron and rudder inputs. The yoke is turned in the direction of the desired turn, and opposite aileron movements create the rolling moment necessary to bank the aircraft. Coupled ailerons are accomplished with a simple set of springs between the yoke and rudder pedals. The yokes turn together because the sprocket is connected by a chain and cable to the opposite side. The yoke allows the pilot to move the airplane over left and over right, controlling the roll axis.
Are ailerons hydraulic?
Modern transport-category aircraft like the A320 employ hydraulically powered ailerons. Each aileron is driven by two hydraulic actuators. Each actuator receives pressure from a different hydraulic circuit so that loss of one line does not eliminate roll control. Either system A or system B can supply enough pressure to move the surface. If both circuits remain healthy the actuators share the load and reduce individual stress. Movement is initiated when control-wheel rotation opens servo valves, allowing hydraulic fluid under pressure to enter the cylinders and convert fluid power into mechanical force.
Within the same surface a spring tab is fitted. The purpose of this tab is to provide a servo-like boost: as aeroload rises, the tab is deflected in the opposite direction, pulling the main surface with it and lessening the pilot's effort. Thus, the spring tab aids movement while the primary hydraulic actuators furnish the muscle.
What is the secondary effect of ailerons?
The secondary effect of ailerons is adverse yaw, which is a result of aileron drag on the upgoing wing. When the pilot rolls the aeroplane by moving the ailerons, the wing whose aileron goes down gains lift and, at the same time, gains induced drag. The opposite aileron goes up and that wing loses lift and its induced drag falls. Because the down-going aileron generates more drag than the up-going one, a yawing moment appears that pulls the nose away from the intended direction of turn which is adverse yaw.
Aileron drag acts like a sideways pressure on the fuselage and fin, swinging the aircraft about the vertical axis. The result is that, if the pilot uses the stick alone, the aeroplane first rolls, then slips, and finally yaws toward the lower wing. The stronger the aileron deflection and the lower the airspeed, the more marked the adverse yaw. Higher flying speed reduces its magnitude.
Designers try to minimize the unwanted yaw by differential aileron travel: the up aileron is allowed to rise farther than the down aileron is allowed to drop, so the extra profile drag on the descending wing partly cancels the extra induced drag on the rising wing. Even so, a high-aspect-ratio configuration cannot entirely avoid the effect. The definitive cure is to use the rudder: a coordinated turn demands that the stick and pedals move together so that yaw is prevented before it starts.
What are the different types of ailerons?
The different types of ailerons are explained 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.
What are differential ailerons?
Differential ailerons are a control-surface arrangement in which the upward-deflecting aileron is displaced a greater distance than the downward-deflecting aileron. This unequal travel is called aileron differential.
What are differential ailerons used for? Engineers developed differential ailerons to reduce the likelihood of wing-tip stall and to combat adverse yaw. Adverse yaw is the unwanted yaw that accompanies roll when the ascending wing produces less drag than the descending wing.
How do differential ailerons work? By moving the upward-deflecting aileron more than the downward-deflecting one, differential ailerons increase drag on the descending wing. The induced drag balances most of the lift-induced drag of the ascending wing, helping to equalize drag on both wings and thereby reducing adverse yaw. Although effective, differential ailerons cannot eliminate adverse yaw entirely and pilots still use coordinated rudder input when necessary.
In a Cessna 172 the left aileron deflects 14 degrees downward while the right aileron moves 20 degrees upward, illustrating typical aileron differential. The de Havilland Tiger Moth, best-known airplane to have differential ailerons, demonstrates the same principle at lower speeds. Modern fly-by-wire systems can continually tailor the amount of differential to whatever part of the flight envelope the aircraft is operating in, sensing sideways G-load and driving it toward zero.
A high-aspect-ratio configuration will not be able to avoid adverse yaw regardless of the degree of aileron differential, and it is impossible to tailor differential to overcome adverse yaw at low speed even for wings of moderate aspect ratio. The need to keep aileron forces growing with deflection angle normally limits how much differential can be applied.
What are frise-type ailerons?
Frise ailerons counter induced drag produced by the downward-moving aileron on the other wing. They have their connecting hinges placed at a distance from the aileron's leading edge. The leading edge of the aileron reduces adverse yaw. Frise ailerons are an aileron having a nose portion projecting ahead of the hinge axis and a lower surface in line with the lower surface of the wing.
Frise ailerons are a type of aileron mounted on the trailing edge of the wings. They were invented by Leslie George Frise, a Bristol Aeroplane Company engineer, and first recorded in 1930-35. The surface is hinged near the bottom and pivots on an offset hinge placed at about 25-30% chord line, so that when the trailing edge is raised the leading edge extends forward of its axis of rotation and protrudes below the bottom surface of the wing. This protruding nose is pushed into the airflow and creates form drag on the upward-deflected side.
Frise ailerons are designed to reduce adverse yaw. The increased profile drag on the descending wing helps equalize the induced drag produced by the downward-moving aileron on the opposite wing, so the drag difference that causes adverse yaw is diminished. At the same time, the offset hinge allows the lowered aileron to form a slot between wing and aileron. The slot allows air to flow smoothly over the lowered surface and improves airflow above the aileron during slow flight, boosting aileron effectiveness at high angles of attack.
What are conventional ailerons?
Conventional ailerons are one of the three primary flight control surfaces, which control an aircraft's rolling motion. An aileron is a controllable hinged panel located on each of the aircraft's wings, typically close to the wingtip, where the pilot controls the aircraft's roll. Some aircraft have differentially controlled spoilers to supplement ailerons.
Conventional hinged ailerons are attached to the outboard trailing edge of each wing where, in early aircraft designs, they moved equally but in opposite directions. The C172P has conventional hinged ailerons. Non-conventional ailerons include the inboard or high-speed ailerons that replace outboard surfaces on some production aircraft. These are located nearer the root to lessen the dangerous tendency of tip-mounted surfaces to stall if used aggressively.
What is the difference between ailerons and flaps?
Ailerons and flaps are both control surfaces on an aircraft's wings but serve distinct purposes. Ailerons control the roll of the aircraft while flaps increase lift and drag. Ailerons are positioned near the wing tips and pivot differentially to control roll. Flaps are mounted on the inboard section of each wing. Flaps are used to increase the lift or drag on both wings equally, enhancing lift at lower speeds during takeoff and landing, while ailerons control the roll by altering lift asymmetrically between the wings, crucial for steering and horizontal maneuvers. Flaps allow an aircraft to fly slower without stalling.
What is the difference between ailerons vs rudder?
The main difference between ailerons and rudders is that rudders correct the adverse yaw created by the ailerons. Ailerons are hinged flaps on the trailing edges of an aircraft's wings that control roll by moving in opposite directions, allowing pilots to bank and turn. When the pilot turns the control yoke right, the right aileron goes up (decreasing lift on that wing) and the left aileron goes down (increasing lift on that wing), causing the plane to roll right; the opposite happens for a left roll.
A rudder is a movable control surface on the trailing edge of the vertical stabilizer that controls yaw, the side-to-side movement of the nose, allowing the pilot to steer left or right around the vertical axis, crucial for coordinated turns, directional control, and counteracting adverse yaw from other controls like ailerons.
