"Kurt R. Todoroff" wrote in message
...
Flaps and slats increase the wing camber which produces obvious
advantages.
Extensible flaps and slats increase the wing area which produces obvious
advantages.

The slat (not to be confused with the leading edge flap) energizes the
upper
surface boundary layer, thus delaying upper surface flow separation and
stall.
This effect increases the stall angle-of-attack, increases directional
stability, but sometimes increases or decreases the coefficient of lift,
depending on the wing system design.

The net effect of both slat and flap extension working in unison is to
increase
lift, increase stall angle-of-attack, and increase directional stability.
This
serves to reduce the landing speed. It also serves to increase aircraft
"G"
(normal acceleration) above the clean wing value at a given airspeed.

Very nice, Kurt.