Leading-Edge Slat

A leading edge slat is an aerodynamic surface fitted to the leading edge of a fixed wing aircraft's wing, sitting flush against the wing when retracted and sliding forward when deployed to open a narrow slot between itself and the wing ahead of it. Air flowing beneath the slat is directed through that slot and re-energizes the boundary layer on top of the wing, which has otherwise lost speed and lift generating capacity as the aircraft slows, letting the wing reach a higher angle of attack before it stalls and so allowing the aircraft to fly, take off and land at slower speeds over shorter distances. Slats can be automatic and spring loaded, extending on their own as the aircraft slows, fixed permanently in the extended position on some low speed aircraft, or powered and controlled directly by the pilot as on most airliners. The German engineer Gustav Lachmann developed the idea in 1918 and filed a German patent that was initially rejected, while Handley Page Ltd in Britain developed a slotted wing independently and patented it in 1919; the two parties later reached an agreement to share the invention rather than dispute it, and the first test flight of a slatted wing took place in 1919 on an Airco DH.9.