Slats are aerodynamic surfaces on the leading edge of the wings of 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 product of angle of attack and speed, so by deploying slats an aircraft can fly slower or take off and land in a shorter distance. They are usually used while landing or performing maneuvers which take the aircraft close to the stall, but are usually retracted in normal flight to minimize drag.

Types

Types include:

• Automatic - the slat lies flush with the wing leading edge until reduced aerodynamic forces allow it to extend by way of springs when needed. This type is typically used on light aircraft.
• Fixed - the slat is permanently extended. This is sometimes used, especially on specialist low-speed aircraft (these are referred to as slots).
• Powered - the slat extension can be controlled by the pilot. This is commonly used on airliners.

Operation

The chord of the slat is typically only a few percent of the wing chord. They may extend over the outer third of the wing or may cover the entire leading edge. Slats work by increasing the camber of the wing, and also by opening a small gap (the slot) between the slat and the wing leading edge, allowing a small amount of high-pressure air from the lower surface to reach the upper surface, where it helps postpone the stall.

The slat has a counterpart found in the wings of some birds, the alula a feather or group of feathers which the bird can extend under control of its "thumb".

History

Slats were first developed by Gustav Lachmann in 1918. A crash in August 1917, with a Rumper C aeroplane on account of stalling caused the idea to be put in a concrete from, and a small wooden model was built in 1917 in Cologne. In 1918, Lachmann presented a patent for leading edge slats in Germany. However, the German patent office at first rejected it as the office did not believe in the possibility of increasing lift by dividing the wing.1.

Independently of Lachmann, Frederick Handley-Page in in Great Britain also developed the slotted wing as a way to postpone stall by reducing the turbulence over the wing at high angles of attack, and formally patented it in 1919; to avoid a patent challenge, the wealthy Handley Page offered Lachmann a job, which he accepted. That year a DeHaviland DH9 was fitted with slats and flown. Working with at the Handley-Page aircraft company, Lachmann was later responsible for a number of aircraft designs, including the Handley Page Hampden.

Licensing the design became one of the company's major sources of income in the 1920s. The original designs were in the form of a fixed slot in the front of the wing, a design that was found on a number of STOL aircraft.