FAA Flight Instructor Airplane (FIA)Aerodynamics and Principles of FlightMedium
A CFI is explaining fixed leading-edge slots to a client comparing high-lift devices. Which statement correctly describes how slots improve wing performance at high angles of attack?
- ASlots reduce the wing's effective camber, which lowers CLmax but improves cruise efficiency
- BSlots channel high-energy airflow from below the wing over the upper surface, re-energizing the boundary layer and delaying separation, which increases the critical angle of attack and CLmax
- CSlots function only when manually extended by the pilot during approach, similar to flaps
- DSlots primarily increase the wing's effective aspect ratio, reducing induced drag at cruise speeds
Show answer & explanationAnswer & explanation
Correct answer: B. Slots channel high-energy airflow from below the wing over the upper surface, re-energizing the boundary layer and delaying separation, which increases the critical angle of attack and CLmax
Leading-edge slots direct a high-velocity stream of air over the upper wing surface at high angles of attack, energizing the boundary layer so it remains attached longer, delaying separation and increasing both the critical angle of attack and CLmax.
Why the other options are wrong
- A. Wrong — slots increase, not decrease, effective lift capability at high AOA
- C. Wrong — many slots are fixed and operate automatically without pilot action
- D. Wrong — slots affect boundary layer behavior, not aspect ratio
Leading-Edge Slots
Fixed or automatic openings near the wing's leading edge that direct high-energy airflow over the upper surface, delaying boundary layer separation and increasing stall angle of attack.
- Increase both critical AOA and CLmax
- Can be fixed or automatic (slats that extend under aerodynamic load)
- Different from flaps, which primarily increase camber
Memory trick: Slots = a garden hose feeding fresh energy onto a tired boundary layer