MOHR1951
The F-16 and FA-18 have leading edge FLAPS. They are hinged off of the leading edge spar and work in concert with the trailing edge ailerons and flaps. The LE flaps alter camber and are capable of independent movement relative to each other, depending on flap and aileron control commands. They not only alter camber for lift enhancement, but add roll-rate when differentially activated... which is necessary with very heavy wing-store loads [high roll inertia]. In addition these devices have a secondary but very important function: when roll is commanded using ailerons or flaperons together there is a very serious torque on the wing-box; the LE Flaps generate opposite torque-loads [relative to the trailing edge control surfaces] providing a counter-torque to the wing box. The LE Flap counter-torque is essential for minimizing wing aeroelastic twist that could add very high/runaway/destructive torque-loads to the wing-box. Essentially the 'active' LE flaps, independently controlled by the computers, allow the jets to see MUCH higher wing [lift/roll/dynamic] loads than static structure would permit.
Wing leading edge SLATS are like traditional flaps in that they function 'in concert' [same movement, LH RH wings] and are exclusively for lift enhancement. All slats that I'm aware of, actually push-away from the wing-box... which has a second stub leading edge sculpted under the slat... which does 3 things: (a) increases wing-area as the slat moves forwards; (b) forms an aerodynamic gap between the SLAT and the wing structure that forces entrapped airflow [thru the gap] over the wing upper surface to the trailing edge; and (c) in concert with the wing trailing edge FLAPS [which usually increase wing-area aft-ward while increasing camber and torque] tend to balance wing-box torque loads. This would be typical for most new transport acft.
NOTE. The SLATS added wing leading edges of older fighters [F-4, F-100, etc]... where flaps/ailerons are hinged off the rear spar... and were intended [added] for airflow control to enhance fighter lift/roll maneuverability for low-to-high subsonic dog-fight speeds [enhance lift and delay stall when in high G pitching/rolling maneuvers].
NOTE. SOME older Boeing transports [707, 727] have both 'plain leading edge flaps' and SLATS. The plain LE Flaps hinge-down from the under the leading edge to increase camber [primarily in the 'thick' LE area of the inner 1/3 of the wing LE span]... and have the classic extendable/flow-gap SLATS on the outer ~2/3's of the wing LE span. for enhanced lift and roll-controllability.
NOTE.
Some STOL aircraft have SLATS for all the purposes mentioned... but especially for enhancing lift and roll control... so they can safely fly at ridiculously low airspeeds.
Regards, Wil Taylor
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