Both flaps and ailerons are hinged panels on the trailing edge of a wing, yet they serve different functions. Flaps, mounted nearer the wing root, increase camber and surface area, raising the maximum lift coefficient and lowering stall speed so the aircraft can fly safely at lower velocities. Ailerons, positioned closer to the tips, move up and down in opposite directions to command roll.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the difference between aircraft flaps and ailerons?
Flaps are high-lift devices which when extended increase the camber and thereby the lift. Ailerons are primary roll controls: when one aileron lifts and the other drops, lift is reduced on one wing and increased on the other, so the airplane rolls. Flaps are used symmetrically for take-off and landing whereas ailerons are always used asymmetrically to turn or balance the aircraft. Thus, flaps and ailerons share the same location at the wing trailing edge, but their purpose and motion are fundamentally different.
Where are flaps and ailerons located on an aircraft?
Flaps are located on the trailing edge of the wing, positioned in the inboard section near the wing roots. Ailerons are located on the trailing edge of the wing near the wingtips.
How do flaps and ailerons affect aircraft control?
Flaps are secondary flight controls that help modify lift and drag at low airspeed and high angle of attack, and their movement influences roll. An asymmetric lowered flap causes a roll moment away from it, and a split-flap situation - one flap down, the other up caused by linkage malfunction - abruptly banks the aircraft. Thus, while flaps are not primary roll devices, any asymmetric deployment demands prompt pilot compensation through aileron and rudder pressure to maintain safe aircraft control.
Movement of any of the three primary flight control surfaces - aileron, elevator, rudder - changes the airflow and pressure distribution over the airfoil. Primary flight controls directly control the plane's movement about its longitudinal, lateral, and vertical axes. Adjusting aileron deflection helps manage the aircraft's roll; one aileron moves up while the opposite moves down, banking the airplane left or right. This asymmetric lift also generates adverse yaw, meaning the nose yaws opposite to the aileron application, so simultaneous rudder input is necessary to counteract the resultant adverse yaw. Frise ailerons, spoilerons on the upper wing surface, or coupled systems are designed to further reduce adverse yaw.
When are flaps used compared to ailerons on an aircraft?
Flaps are used during takeoff and landing and are retracted during cruise. During takeoff, a partial setting - usually between five and fifteen degrees - lets the wing generate more lift at lower speed, so the airplane leaves the ground sooner.
In flight, only ailerons move: one aileron goes up while the other aileron goes down to roll the aircraft. Flaps stay motionless because they are not needed once the wing is already producing adequate lift. During approach and landing, the pilot extends the flaps further. This increases both lift and drag, allowing a slower, steeper descent without gaining speed.
Which creates more lift: flaps or ailerons?
Flaps produce more lift than ailerons. Lowered flaps increase camber and wing area thereby creating more lift. Split, plain and slotted types all add lift, with slotted flaps producing much greater increases in maximum coefficient of lift than plain or split flaps. Leading-edge flaps also provide additional lift. Flap deployment angle determines the amount of additional lift gained.
Lift byproduct is drag. Because flaps create more lift, they add a lot of drag. Split flaps produce slightly more lift than plain flaps but a lot more drag. Larger wing area adds to drag as well. Landing requires high lift and high drag, so large flap angles are used. Takeoff needs high lift and low drag, so smaller flap settings are preferred, for smaller angles increase lift over drag. Greater angles increase drag over lift dramatically.
Downward deflection of the left aileron increases camber, resulting in increased lift on the left wing, yet the same motion also generates more induced drag. Adverse yaw is created due to the drag differential between the two sides of the aircraft. Despite this, the total lift change from a single aileron is minor compared with symmetric flap deployment.
Flap extension delays stall. Airflow smoothing delays stall onset, permitting slower flight. The aircraft can therefore fly at lower speed without stalling when flaps are extended.
How are flaps controlled compared to ailerons?
On most aeroplanes the pilot moves a single lever, and both flaps on each wing are moved together. They extend and retract at the same rate, driven by one motor or one hydraulic line. Ailerons are wired to the control wheel or stick: when the wheel turns left, the left aileron rises and the right one falls.ilerons never move in unison.
A mixer combines the flap command and the roll command so the surfaces obey one surface law: when the pilot calls for more lift the surfaces drop together, and when he calls for bank the surfaces move opposite, just as flaperons control the bank angle like conventional ailerons.
Modern aircraft actuate control surfaces with electric motors, yet the principle is unchanged - flaps have almost no leverage for roll, so the mixer keeps the two commands apart and the motion is seamless.
What are the advantages and disadvantages of flaps?
Advantages of flaps are that they lower an airplane's stall speed, allowing aircraft to fly slower without stalling. This slower speed lets pilots approach runways more slowly and land within shorter distances. Flaps permit a steep descent angle without airspeed increase, so airplanes can descend at steeper angles without gaining speed. During takeoff, flaps enable the aircraft to lift off sooner and use less runway, reducing takeoff distance. While all flap types add camber to the wing, together the extra area and increased camber boost lift at low speed. Because drag rises when flaps extend, flap extension during landings provides greater drag, which helps slow the aircraft and reduces the length of the landing roll.
The same drag that aids descent and rollout brings drawbacks. A large aft-projected area of the flap increases the drag of the aircraft, raising fuel consumption during any phase of flight when flaps remain extended. The added drag shortens range and climb performance, so pilots must retract flaps as soon as possible. Increased camber and flap deflection also change pitching moments, requiring trim corrections and increasing pilot workload. When fully extended for landing, flaps create nose-down pitching moments and reduce the margin against tail strikes on flare. Mechanical complexity is another disadvantage: tracks, rollers, and hinges add weight and present more surfaces to ice or fail, so maintenance costs rise.
What are the advantages and disadvantages of ailerons?
Ailerons have the advantage of not weakening the airplane's wing structure, a weakness that plagued the older wing-warping technique. By moving one surface up and the other down, they help the plane bank left or right without twisting the entire wing. This differential lift tilts the aircraft about its longitudinal axis, letting it follow a curved flight path while the structure remains intact.
Roll control at high speeds does not bend the wing excessively, so fighters and aerobatic stunt airplanes can maneuver sharply without damage. Differential and frise ailerons reduce adverse yaw, the unwanted yawing moment opposite to the roll direction, refining handling during quick turns. Telescopic sticks give the pilot a longer lever arm at high speed, keeping stick forces low while precision remains high. In conjunction with rudder input, ailerons help maintain a coordinated turn, cancelling the crab angle caused by extra drag from the descending aileron.
Disadvantages of ailerons are that they generate adverse yaw that must be countered by deliberate rudder deflection, adding pilot workload. Gap seals, bleed-air systems and coupled controls add complexity, weight and maintenance demands. Seals on vented ailerons are delicate and must be kept clean. At very high speed, actuator loads rise, and on unstable high-maneuverability designs any aileron failure quickly spoils lateral stability.
