Slats, Slots and Spoilers – Lift Modifying Devices on Airplane Wings


Home / Slats, Slots and Spoilers – Lift Modifying Devices on Airplane Wings

How Slots Work:

Primitive leading edge devices were the fixed slots. Installed aft of the leading edge, outboard of the wing and in-line with the ailerons.

The fixed slot of a Stinson 108-1: A leading edge, high lift device. Photo Credit: Christopher Ebdon

As an aircraft approaches the stall angle of attack, the separation point moves forward, towards the leading edge. This results in a turbulent flow of air over the wing surface (just behind the separation point) and a drastic loss of lift beyond the stall angle of attack. Moreover, a turbulent airflow over the wing reduces control effectiveness:  ailerons would not efficiently bank the plane!

To counter this lack of aileron efficacy, “The high-pressure air below the wing is drawn up through the slot and flows over the top of the wing. This energizes the boundary on top of the wing”, explains David F. Anderson and Scott Eberhardt in Understanding Flight.

Slots help regain aileron effectiveness at high angles of attack and are also responsible for about a 40% increment in the airplane wings’ lifting capability.

Slats and Slots

Slats slide out on operation, and are a simple extension of the plane’s leading edge as they create a slot, hence improving the lift producing characteristics of the aircraft wing at slow speeds. Spoilers, on the other hand, deflect upwards to kill the lift generated by the wings. By using the variable surfaces on a plane’s wings, pilots can maneuver an aircraft efficiently by allowing numerous settings (in combination) for these control surfaces.

The fixed leading edge slats of a Fieseler Fi-156C-3. Photo Credit: Johnny Comstedt


Aviation Theory Centre. Aeroplane General Knowledge and Aerodynamics. (2004).

Federal Aviation Administration. Pilots Handbook of Aeronautical Knowledge. (2008). Accessed April 4, 2012.

Federal Aviation Administration. Airplane Flying Handbook. (2004). Accessed April 4, 2012.

NASA Glenn Research Center. Spoilers. Accessed April 4, 2012.

Anderson, D., Eberhardt, S. Understanding Flight. (2000). McGraw-Hill.

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