Which flap type slides backwards before hinging downward, increasing both camber and chord, creating a larger wing surface better tuned for lower speeds?

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

Answer: (D)

The key idea is high-lift effect achieved by increasing the wing surface along with camber. This flap type moves backward along tracks before dropping down, which slides more of the wing’s surface from behind the trailing edge and also tilts it downward. By extending the trailing edge rearward and deflecting it, both the chord (the wing’s depth) and the camber increase, giving a larger wing area overall. That bigger wing surface plus the shape change boosts the lift coefficient at lower speeds, making takeoffs and landings safer and shorter.

Other flaps achieve lift in different ways without the same simultaneous growth in wing area. A plain flap only deflects downward to increase camber, without adding significant wing area. A slotted flap adds a gap to energize the airflow and improve lift, but it doesn’t move the flap backward to enlarge the wing surface. A split flap deflects downward on the lower surface to several effects, mainly increasing drag and some lift, without appreciable increase in wing area.

So, the mechanism described—sliding backward to increase both camber and chord and thus wing surface—matches the Fowler flap.