Leading-edge slat

Slats are aerodynamic surfaces on the leading edge of the wing of a fixed-wing aircraft which, when deployed, allow the wing to operate at a higher angle of attack. A higher coefficient of lift is produced as a result of angle of attack and speed, so by deploying slats an aircraft can fly at slower speeds, or take off and land in shorter distances. They are used during takeoff and landing or while performing low speed maneuvers which may take the aircraft close to a stall. Slats are retracted in normal flight to minimize drag. Slats are high-lift devices typically used on aircraft intended to operate within a wide range of speeds. Trailing-edge flap systems running along the trailing edge of the wing are common on all aircraft. Types include: Automatic The spring-loaded slat lies flush with the wing leading edge, held in place by the force of the air acting on them. As the aircraft slows down, the aerodynamic force is reduced and the springs extend the slats. Sometimes referred to as Handley-Page slats. Fixed The slat is permanently extended. This is sometimes used on specialist low-speed aircraft (these are referred to as slots) or when simplicity takes precedence over speed. Powered The slat extension can be controlled by the pilot. This is commonly used on airliners. The chord of the slat is typically only a few percent of the wing chord. The slats may extend over the outer third of the wing, or they may cover the entire leading edge. Many early aerodynamicists, including Ludwig Prandtl, believed that slats work by inducing a high energy stream to the flow of the main airfoil, thus re-energizing its boundary layer and delaying stall. In reality, the slat does not give the air in the slot a high velocity (it actually reduces its velocity) and also it cannot be called high-energy air since all the air outside the actual boundary layers has the same total heat. The actual effects of the slat are: The slat effect The velocities at the leading edge of the downstream element (main airfoil) are reduced due to the circulation of the upstream element (slat) thus reducing the pressure peaks of the downstream element.