Slats are most effective at:

• A. High AoA
• B. Low AoA
• C. Cruise AoA
• D. Zero AoA

Answer: (A)

Slats are leading-edge devices that create a small gap when extended, which accelerates airflow to the wing’s upper surface. This added airflow energizes the boundary layer and delays flow separation, allowing the wing to achieve a higher angle of attack before stalling. That lift-boosting effect is most valuable when the wing is already near stall, such as during takeoff or landing phases. At high angles of attack, the slats meaningfully increase maximum lift and improve stall characteristics, while at cruise or low angles of attack they mainly add drag without a substantial lift gain. So slats are most effective at high angle of attack.