Definition
A plain hinge, in the context of wing flaps, is the simplest type of flap construction in which the flap is attached to the wing by a basic hinge along its leading edge, allowing it to rotate downward as a single rigid panel. When deflected, a plain flap increases both the camber and the effective angle of attack of the wing, producing more lift and more drag, but it does not slide rearward or open any slots between itself and the wing.
Plain English
A plain flap is the most basic kind of flap. It is fixed to the back of the wing by a simple pivot, so when the pilot lowers it, the flap just swings down like a door on a hinge.
Context Anchor
Seen when comparing flap designs and flap effectiveness in the Airplane Flying Handbook.
Derivation
"Plain" comes from the Latin planus, meaning flat or simple. It is used here to signal that this hinge arrangement has no extra mechanism — no sliding tracks, no slots, no separate panels — just a straightforward pivot.
Why Pilots Care
Affects how much extra lift and drag the flaps produce when extended, which changes stall speed and landing distance.
Intuition Check
Plain does not mean ordinary in a vague way here. It means simple in design: one fixed hinge action, without extra movement or added airflow paths.
Example Sentence 1
The training aircraft uses a plain hinge flap design, so lowering the flaps simply pivots them down from the trailing edge of the wing.
Example Sentence 2
Because the flaps use a plain hinge, full deflection creates more drag than a slotted design would at the same angle.