What is flap and slat ?

1. Flaps : It is secondary control surface . It is installed in trailing edge of  the wings towards in - board section of wing . At the time of landing and takeoff the aircraft speed is slow which can not produce sufficient lift to support the aircraft in air , according to lift formula with increase in co-efficient of lift or surface area of wing the lift increases . By extending the flaps it increases the surface area as well as camber of wing . Flaps are mainly used at time of landing but partially at the time of take off , because when flaps are full extended it produce more drag with little increase in lift .
   
2. Slats : It is also secondary control surface . It is installed in leading edge of the wing in outboard section of wing . It also used at the time of takeoff and landing  .It may be automatically operated or manually  operated . It extended in front of leading edge over the track . When it exdend it provied a slote between wing surface and itself to allow airflow from it . By allowing the air flow smoothly over the wing it energize the boundary layer by which it increases the velocity of air flow which increase the lift production .