What are Slats?
Slats, also known as Leading Edge Devices, are extensions to the front of a wing for lift augmentation, and are intended to reduce the stalling speed by altering the airflow over the wing. Slats may be fixed or retractable - fixed slats (e.g. as on theFieseler Fi 156 Storch) give excellent slow speed andSTOLcapabilities, but compromise higher speed performance. Retractable slats, as seen on most airliners, provide reduced stalling speed for take-off and landing, but are retracted for cruising.
The actual effects of the slat are (according to Wikipedia):
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The slat effect: The velocities at the leading edge of the downstream element (main airfoil) are reduced due to the circulation of the upstream element (slat) thus reducing the pressure peaks of the downstream element.
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The circulation effect: The circulation of the downstream element increases the circulation of the upstream element thus improving its aerodynamic performance.
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The dumping effect: The discharge velocity at the trailing edge of the slat is increased due to the circulation of the main airfoil thus alleviating separation problems or increasing lift.
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Off the surface pressure recovery: The deceleration of the slat wake occurs in an efficient manner, out of contact with a wall.
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Fresh boundary layer effect: Each new element starts out with a fresh boundary layer at itsleading edge. Thin boundary layers can withstand stronger adverse gradients than thick ones.
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”.
I got some of these from:
http://en.wikipedia.org/wiki/Leading_edge_slats
