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Use for high-lift devices such as flaps, slats, slots, etc.

High-lift devices are parts of an aircraft used to increase the amount of it can generate, and thereby increase the aircraft's payload capacity and/or decrease its and speeds. Most high-lift devices are placed on either the leading or the trailing edges of the wings, but high-lift devices in other places also exist:

  • Leading-edge devices are, as the name indicates, located on the wing's leading edge. Although they do directly increase the wing's lift by a small amount, their main benefit is to increase the at which the wing experiences a , allowing the wing to be rotated to a higher angle of attack (and, thus, be made to produce more lift) before it stalls.
    • Droops are hinged sections of the wing's leading edge that can be rotated downwards to increase the wing's camber (the curvature of its upper surface).
    • are movable sections of the leading edge which slide forwards and downwards, simultaneously increasing the wing's camber and opening up a slot in the wing just behind the leading edge.
    • Slots are similar to slats, but, instead of extending and retracting, they are fixed in the extended position, leaving the wing with a permanent slot (hence the name) immediately behind its leading edge.
    • Krueger flaps, despite their name, are more akin to other leading-edge devices than to trailing-edge flaps; they consist of panels under the wing's leading edge, hinged at their front end, which swing out from under the wing to increase the camber of the wing's leading edge. This is much simpler to show than it is to describe; a diagram is probably in order:how ye olde krueger flap works (Image by Stahlkocher and HDP at Wikimedia Commons.)
    • A leading-edge root extension (LERX) is a long, narrow, triangular panel extending forward along the fuselage from the leading edge of the wing root, creating a over the upper surface of the wing and preventing the airflow over the wing from separating from it (the wing).
    • A cuff or dogtooth is a sharp, zigzag discontinuity in the wing's leading edge, which produces vortices that keep a stall from progressing outboard beyond the discontinuity.
  • Trailing-edge devices are located, surprise surprise, on the wing's trailing edge. They work by directly increasing the amount of lift produced by the wing at a given angle of attack.
    • The major trailing-edge devices of note are , a large family of devices which generally increase lift by increasing the wing's area, its camber, or both.
    • The flap function can also be combined with an aircraft's as a , which allows a single set of surfaces to serve double duty for lift enhancement and roll control (instead of requiring two dedicated sets, one for each function), reducing weight.
  • High-lift devices not attached to either the leading or trailing edges include:
    • Boundary-layer control systems (BLCSs) blow high-energy air (usually from the engine(s)) into the thin "boundary layer" next to the surface of the wing, reenergising this layer and making it more resistant to separating from the wing at high angles of attack.
    • cause the airflow along the wing's upper surface to curl up into narrow vortices which stick to the wing's surface more readily than non-vortex air, allowing this airflow to remain attached to the wing at higher angles of attack.
    • Nose strakes are like LERXs, but are mounted ahead of the wing instead of being attached to it.

For more information, see the Wikipedia pages on: