Definition
A surface that curves inward, forming a hollow or cupped shape, as opposed to one that bulges outward. In aircraft structures and components, a concave surface is one whose interior side is the curved-in face — for example, the inner face of a fuselage skin panel or the dished face of certain rivet heads, formed sheet metal parts, or composite layups.
Plain English
A surface that curves inward, like the inside of a bowl or spoon.
Context Anchor
Seen in aircraft structure, skin, repair, and inspection descriptions when the shape of a part or damaged area is being described.
Derivation
From the Latin concavus, meaning 'hollow' or 'arched inward.' The 'cav' part shares a root with 'cave' — a hollowed-out space. That image is exactly right: a concave surface is the cave-side of a curve.
Why Pilots Care
A concave area on an aircraft surface may show a dent, damage, or an intended shape, and the difference matters during inspection and repair.
Analogy
The inside of a satellite dish or the bowl of a spoon — that curved-in face is the concave surface. The outside of the same dish or spoon is convex.
Intuition Check
Do not confuse concave with a surface that bulges outward. Concave means inward-curving or hollowed in.
Example Sentence 1
The technician inspected the concave surface of the fuselage skin panel for cracks before reinstalling it.
Example Sentence 2
A concave surface on the formed rib allowed the rivets to sit flush with the structure.