Definition
The minimum radius to which a tube, hose, sheet metal, or wire bundle can be bent without weakening, kinking, cracking, or damaging the material. It is measured from the centerline of the bend to the inside surface of the bent material, and minimum allowable values are specified by the manufacturer or applicable maintenance standards.
Plain English
How tight a curve you are allowed to put into something — like a metal tube or a wire bundle — before you start damaging it. Bend it sharper than the allowed amount and it can crack, kink, or fail.
Context Anchor
Seen in aircraft sheet metal repair, tube bending, fabrication drawings, and maintenance instructions that tell how a part may be bent without damaging it.
Derivation
From 'bend' (to curve) and 'radius' (the distance from the center of a circle to its edge). The bend in a tube or sheet follows the curve of an imaginary circle, and the radius of that circle is what's being measured.
Why Pilots Care
Using too tight a bend can damage wiring insulation or fluid lines, leading to chafing, leaks, or system failure in flight.
Analogy
Like the minimum curve radius on a garden hose: bend it sharper and it kinks and stops the flow.
Intuition Check
Do not read bend radius as just “the amount of bend.” It is the size of the curve of the bend, measured as a radius, so it describes how tight or broad the bend is.
Example Sentence 1
Before installing the new hydraulic line, the technician checked the manufacturer's minimum bend radius to make sure the routing wouldn't kink the hose.
Example Sentence 2
Exceeding the minimum bend radius while routing the avionics wiring caused insulation cracks that later triggered intermittent faults.