Flap ( aircraft ) Flaps are hinged surfaces on the trailing or leading edge of the wings of a fixed-wing aircraft which , when deployed , increase the lift and drag of a wing . Lift is increased by : increasing the camber of the wing . increasing the size of the effective lifting surface by increasing the wetted area . Drag is increased by : increasing the wetted area of the wing , resulting in more skin friction drag . increasing the induced drag of the wing . Flaps are usually fully extended while landing to allow the aircraft to fly more slowly ( by increasing the lift generated by the wings at slow speeds ) and to steepen the approach to the landing site . Depending on the aircraft type , configuration and method of takeoff ( e.g. , short field , soft field , normal , etc. ) , flaps are often partially extended for take-off to give the aircraft more lift when trying to leave the ground . Some gliders not only use flaps when landing but also in flight to optimize the camber of the wing for the chosen speed . At lower speeds when thermalling , positive flap is used , i.e. , flaps are lowered . At higher speeds a negative flap setting is used , i.e. the flaps are raised . Negative flap is also used during the initial stage of an aerotow launch and at the end of the landing run in order to maintain better control by the ailerons . Triple-slotted trailing-edge flaps on a Boeing 747 fully extended for landing at Heathrow Airport , London . Four types of flaps Types of flap systems include : Kruger flap - Droop flap on the leading edge Plain flap — rotates on a simple hinge . Split flap — upper and lower surfaces are separate , the lower surface operates like a plain flap , but the upper surface stays immobile or moves only slightly . Fowler flap — slides backwards before hinging downwards , thereby increasing both camber and chord , creating a larger wing surface better tuned for lower speeds . Fairey-Youngman flap - moves bodily down before moving aft and rotating . Slotted flap — a slot ( or gap ) between the flap and the wing enables high pressure air from below the wing to re-energize the air blowing over the flap . This helps the airflow to stay attached to the flap , delaying the stall . Blown flaps — systems that blow engine air over the upper surface of the flap at certain angles to improve lift characteristics . Slats , also known as leading-edge flaps , have a similar purpose to trailing-edge flaps , save they are located on the leading edge of the wing . See also Flight controls Aileron High-lift device Categories : Aircraft controls In other languages : Dansk | Deutsch | Español | فارسی | Français | 한국어 | Bahasa Indonesia | Italiano | עברית | Nederlands | Polski | Português | Suomi 