An example of flaps with a combined design is the ____ flap.

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

Answer: (A)

The idea being tested is how combining mechanisms in flaps enhances lift and control at high angles of attack. A Fowler flap is designed to move backward and downward, increasing both the wing area and the camber, which boosts lift. If that Fowler design includes a slot between the flap and the wing, air from beneath the wing can flow through the slot to the upper surface, re-energizing the boundary layer and delaying separation. This combination—extension of the flap surface plus a slot—provides greater lift and better stall behavior than a plain flap or a simple Fowler flap. The leading-edge Krueger flap isn’t a trailing-edge Fowler-type, and a plain flap lacks the added effectiveness of the slot. So, the example of flaps with a combined design is the slotted-Fowler flap.