Purpose and Development
15° is a typical angle of attack at the stall of a basic airfoil. Modification of such an airfoil by use of a leading edge slot could increase the stalling angle to 22° to 25°.
Slots were first developed by Handley-Page in 1919, and the first aircraft to fly with them was the experimental H.P.17 - a modified Airco DH.9A. The first aircraft fitted with controllable slots was the Handley Page H.P.20. Licensing the design became one of Handley-Page’s major sources of income in the 1920s.
Similar, but retractable, leading edge devices are called slats. When the slat opens, it creates a slot between the slat and the remainder of the wing.
A fixed leading edge slot can increase the maximum lift coefficient of an airfoil section by 40%. In conjunction with a slat, the increase in maximum lift coefficient can be 50% or even 60%.
Unlike trailing edge flaps, leading edge slots do not increase the lift coefficient at zero angle of attack.
Read more about this topic: Leading Edge Slot
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