What is the purpose of high lift devices such as slats and slots?

• A. To increase lift at low speeds.
• B. To reduce weight.
• C. To generate thrust.
• D. To retract flaps during flight.

Answer: (A)

High lift devices are used to increase the wing’s lift at low speeds, allowing safer takeoff and landing. When slats are extended or a slot is opened, air from below the wing can flow to the top surface at a higher energy level, energizing the boundary layer and delaying flow separation as the angle of attack increases. This raises the lift coefficient and lowers the stall speed, so the airplane can fly or land at slower speeds. They’re retracted in cruise to reduce drag, and they don’t reduce weight, generate thrust, or serve as the mechanism for retracting flaps.