Definition
In the context of wing flaps, 'plain' describes the simplest type of flap design: a hinged section of the trailing edge of the wing that pivots downward as a single piece to increase the wing's camber, producing more lift and more drag at a given airspeed.
Plain English
A plain flap is the most basic kind of flap — just a piece of the back edge of the wing that swings down on a hinge to help the airplane fly more slowly and descend more steeply.
Context Anchor
Seen in discussions and diagrams comparing flap types, especially during slow-speed flight, approaches, and landings.
Derivation
Plain' here means 'simple, without added features.' It comes from Latin planus, meaning flat or straightforward. Used as a descriptor, it signals that this flap has no slots, tracks, or moving extensions — just a hinge.
Why Pilots Care
Knowing the plain flap's behavior helps predict handling changes and required power adjustments during approach.
Intuition Check
Plain does not mean “ordinary” in a vague way here. It means the basic hinged flap type, as opposed to more complex flap designs.
Example Sentence 1
The trainer was fitted with plain flaps, so the pilot expected modest extra lift and a fair amount of added drag when they were lowered on final.
Example Sentence 2
Plain flaps produce less drag than split flaps when extended to the same angle.