Which type of flaps are characterized by a sliding surface that extends into the airflow?

Slotted flaps are designed with a sliding surface that extends into the airflow, creating a slot between the wing and the flap itself. This slot allows high-energy air from the wing's upper surface to flow into the flap's lower surface. The result is an increase in lift at higher angles of attack and helps to delay airflow separation over the wing, improving stall characteristics.

The operation of slotted flaps makes them particularly effective for enhancing aircraft performance during takeoff and landing phases. This unique design feature contributes to better lift generation, which is crucial when an aircraft is operating at lower speeds, such as during takeoff and landing. The increased lift efficiency also aids in maintaining controlled flight at these critical phases.

In contrast, the other types of flaps do not share this specific design characteristic. Split flaps, for example, protrude downward from the wing's lower surface but do not have a sliding surface effect like slotted flaps. Fowler flaps extend both downward and rearward but do not utilize a slot for airflow augmentation. Plain flaps simply rotate downwards to increase camber without any sliding surfaces or slots involved. Each of these designs has its distinct performance benefits, but the feature of extending into the airflow distinctly identifies slotted flaps