Plain English Meaning
A surface that curves inward, like the inside of a bowl or spoon.
Full 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.
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.