Definition
A type of wing flap in which only the lower surface of the trailing edge of the wing hinges downward, while the upper surface remains fixed. Deflecting the lower panel increases both lift and drag, allowing a steeper approach angle and lower landing speed without changing the upper wing contour.
Plain English
A flap design where just the bottom skin of the back edge of the wing swings down, while the top of the wing stays put. This adds lift and a lot of drag, which helps the airplane slow down and descend more steeply on landing.
Context Anchor
Seen in aircraft systems descriptions, preflight discussions, and performance information for airplanes equipped with this older style of flap.
Derivation
Called 'split' because the trailing edge is divided — the lower surface moves while the upper surface stays in place, splitting what would otherwise be a single hinged flap into two separate surfaces.
Why Pilots Care
They produce high drag that allows steeper descent angles without building excessive speed, which is useful on short or obstructed runways.
Intuition Check
“Split” does not mean the flap is damaged or divided into two separate left-and-right parts. Here it means the lower surface of the wing moves away from the fixed upper surface.
Example Sentence 1
The DC-3 uses split flaps, which hinge down from the lower surface of the wing to increase drag on landing.
Example Sentence 2
Split flaps on older training aircraft help produce the steep glide path needed for short-field landings.