Leading-edge slot

A leading-edge slot is a fixed aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities.

[2][5] Unlike trailing edge flaps, leading-edge slots do not increase the lift coefficient at zero angle of attack since they do not alter the camber.

At high angles of attack the fastest airspeed relative to the airfoil is very close to the leading edge, on the upper surface.

In this region of high local airspeed, skin friction (viscous force) is very high and the boundary layer arriving at the slot on the upper wing has lost much of its total pressure (or total mechanical energy) due to this friction.

[8] In aircraft other than specialist STOL aircraft, full-span slots have serious drawbacks because, to take advantage of the high angle of attack at the stall, they usually necessitate long undercarriage legs that either cause high drag or are longer than can be accommodated easily inside the airframe.

[2][4] Using slots in this manner produces a similar result to employing washout on a wing, but through a different means.

Examples of aircraft with partial-span, fixed slots are the Stinson 108, Bristol Beaufort, Lockheed Hudson, and Dornier Do 28D-2 Skyservant.