Definition
A straight-line distance from the center of a circle or sphere to any point on its edge. In aircraft maintenance, the term is also used to describe a rounded inside corner or curved edge on a part, where one surface curves smoothly into another rather than meeting at a sharp angle.
Plain English
The distance from the middle of a circle out to its edge. It can also mean a rounded curve where two surfaces meet, instead of a sharp corner.
Context Anchor
Seen in maintenance measurements, curved parts, hose routing, sheet metal bends, and aircraft turning discussions.
Derivation
From the Latin radius, meaning 'spoke of a wheel' or 'ray.' A spoke runs from the hub straight out to the rim — exactly what a radius does on a circle.
Why Pilots Care
On metal parts, sharp corners concentrate stress and become crack starting points. A proper radius (a smooth curve) spreads the load and is often required by the manufacturer. Bending sheet metal too tightly — below the minimum bend radius — can crack the material and ruin the repair.
Analogy
Think of a bicycle wheel spoke. The spoke runs from the hub in the center to the rim; that distance is the radius.
Intuition Check
Radius is not the full width across a circle. It is only the distance from the center to the outside edge.
Example Sentence 1
The technician checked the bend radius against the structural repair manual before forming the new doubler.
Example Sentence 2
When inspecting the propeller, verify the blade tip radius matches the specifications in the maintenance manual.