Leading edge slot
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Leading edge slots are fixed aerodynamic devices used on airplanes. Similar, but retractable, leading edge devices are called slats.
A leading edge slot is a fixed (non-moving) opening behind the wing’s leading edge. The slot does not operate at low angles of attack, like those found in cruise flight. At low angles of attack the airflow just passes over and under the slot.
At progressively higher angles of attack air starts to move through the slot from the higher pressure air below the wing to the lower pressure air on top of the wing. The mixture of the air coming over the leading edge and through the slot has greater momentum and thus sticks to the upper surface of the wing to a higher angle of attack than if the slot were not there.
Leading edge slots are generally of two types: those that are full-span and those that are partial-span.
Full span slots are generally found on Short Take-off and Landing STOL aircraft, like the Zenair CH 701 STOL. Their primary purpose is to lower the stall speed of the aircraft, allowing slower landing speeds and short landing rolls.
Partial-span slots are usually found only on the outboard portion of the leading edge of the wing where they ensure that that part of the wing will remain unstalled at higher angles of attack than the inboard portions of the wing. This ensures the wing root stalls first and contributes to docile stall behaviour and maintaining aileron control throughout the stall. Using slots in this manner produces a similar result to employing washout on a wing, but through a different means. An example of an aircraft with partial span slots is the Stinson 108.
Slots naturally exact a penalty on the aircraft they are used on. This is because at cruise airspeed they create some drag compared to a non-slotted wing and so reduce cruising speed.
One way to reduce the cruise drag of slots is to make them retractable. These are known as leading edge slats. Slats work in the same way as slots but slats retract at higher speeds when they are not needed. Slats, in turn, are heavier and more complex than slots.
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