Definition
A wing flap design in which only the lower surface of the trailing edge hinges downward, while the upper surface of the wing remains fixed. Deflecting the lower panel increases lift and produces significantly more drag than a plain flap, with little change in the wing's upper-surface airflow.
Plain English
A flap where just the bottom skin of the wing's trailing edge swings down, while the top of the wing stays put. It adds lift but creates a lot of drag, which helps the airplane slow down and descend more steeply on landing.
Context Anchor
Seen in discussions of flap design, slow flight, takeoff and landing performance, and how different flap types affect lift and drag.
Derivation
Called 'split' because the trailing edge is split into two surfaces — the upper one stays fixed while the lower one hinges down. The name describes exactly what happens to the wing when the flap is deployed.
Why Pilots Care
Split flaps produce high drag that steepens the approach angle and helps slow the airplane quickly, but they also create a strong nose-up pitching moment that must be managed.
Analogy
Imagine the bottom half of a barn door swinging downward while the top half stays closed; the open lower section catches the air and slows you down fast.
Intuition Check
Split does not mean the left and right flaps move separately. Here, split means the lower surface of the wing separates downward while the upper surface stays mostly fixed.
Example Sentence 1
The trainer's split flaps produced strong drag on final approach, allowing a steeper descent without gaining airspeed.
Example Sentence 2
Because split flaps create a pronounced nose-up pitch change, the pilot applied forward pressure on the yoke as they deployed.