Which flap type is described as having upper and lower surfaces where the lower acts like a plain flap and the upper surface remains largely still?

• A. Plain flap
• B. Split flap
• C. Slotted flap
• D. Fowler flap

Answer: (B)

Flaps change how air flows and the wing’s camber to increase lift at lower speeds. The description here matches a split flap: the lower surface deflects downward like a plain flap while the upper surface remains largely still. Because only the bottom part moves, there’s effectively a separation between the deflected lower surface and the fixed upper surface, which increases lift but also adds significant drag. This is different from a plain flap, which moves as a single piece; a slotted flap, which maintains a gap that energizes the airflow through a slot; or a Fowler flap, which slides rearward to increase wing area and camber, with both surfaces moving.