Which flap design is described as a combined design, according to the source material?

• A. Fowler flap
• B. Krueger flap
• C. Slotted-Fowler flap
• D. Plain flap

Answer: (C)

Combining wing-area increase with airflow control through a slot is what yields a higher lift at high angles of attack. The slotted-Fowler flap does this by moving outward and downward like a Fowler flap, but adds a slot between the flap and the wing. That slot lets air flow from below the wing to the upper surface, energizing the boundary layer and delaying flow separation, which produces more lift without a large penalty in stall characteristics. The other flap types don’t combine these features: a plain flap simply deflects; a Fowler flap increases wing area but without a slot; a Krueger flap is a leading-edge device. So the flap described as a combined design is the slotted-Fowler flap.