drag. Types include plain, slotted, and split. Some, such as Fowler Flaps, also extend rearwards to increase wing area. The Krueger flap is a leading-edge device. Cuff: an extension to the leading edge which modifies the aerofoil section, typically to improve low-speed characteristics. Spanwise flow control On a swept wing, air tends to flow sideways as well as backwards and reducing this can improve the efficiency of the wing: Wing fence: a flat plate extending along the wing chord and for a short distance vertically. Used to control spanwise airflow over the wing. Dogtooth leading edge: creates a sharp discontinuity in the airflow over the wing, disrupting spanwise flow. Notched leading edge: acts like a dogtooth. Vortex creation Vortex devices maintain airflow at low speeds and delay the stall, by creating a vortex which re-energises the boundary layer close to the wing. Vortex generator: small triangular protrusion on the upper leading wing surface; usually, several are spaced along the span of the wing. Vortex generators create additional drag at all speeds. Vortilon: a flat plate attached to the underside of the wing near its outer leading edge, roughly parallel to normal airflow. At low speeds, tip effects cause a local spanwise flow which is deflected by the vortilon to form a vortex passing up and over the wing. Leading-edge root extension (LERX): generates a strong vortex over the wing at high angles of attack, but unlike vortex generators it can also increase lift at such high angles, while creating minimal drag in level flight. Drag reduction Anti-shock body: a streamlined pod shape added to the leading or trailing edge of an aerodynamic surface, to delay the onset of shock stall and reduce transonic wave drag. Sometimes called a Küchemann carrot. Fairings of various kinds, such as blisters, pylons and wingtip pods, containing equipment which cannot fit inside the wing, and whose only aerodynamic purpose is to reduce the drag created by the equipment. Fillet, a type of fairing: a small curved infill at the junction of two surfaces, such as a wing and fuselage, blending them smoothly together to reduce drag. See also Wing § Design features Aircraft design process References Notes Bibliography Kermode, A. C.; Mechanics of Flight, Eighth (metric) edition, Pitman, London, 1972. Taylor, John W. R. The Lore of Flight, Universal Books, London, 1990. . (Archive). External links High wing, low wing—Flight'' article on the merits of