Definition
The natural curve formed by a flexible cable, wire, or chain of uniform weight when it is suspended between two fixed points and allowed to hang freely under its own weight. In aviation, the term most often refers to the slight downward sag designed into long-wire HF antennas and certain control cables, where the curve is an expected and necessary part of the installation rather than a defect.
Plain English
The shape a chain or wire makes when you hold both ends and let the middle sag. In aircraft, some wires and cables are meant to hang in this gentle curve.
Context Anchor
Seen in discussions of suspended wires, cables, antennas, and other hanging lines around aircraft or airport areas.
Derivation
From the Latin catena, meaning chain. The word was coined to describe the exact curve a hanging chain forms — so the name literally means 'chain-shaped curve.' Knowing this makes the term easy to picture: a chain held at both ends.
Why Pilots Care
Pilots care because wires and cables do not usually run in a straight line between supports. Their lowest point may be between the supports, which matters when operating close to the ground.
Analogy
Think of a power line strung between two poles — it never hangs in a straight line; it always dips slightly in the middle. That dip is a catenary curve.
Grounding Statement
Picture a power line between two poles: it is higher near the poles and hangs lower in the middle.
Intuition Check
A catenary curve is not just any curved line. It is the specific sagging shape made by a hanging flexible line under its own weight.
Example Sentence 1
The HF antenna wire is rigged with a slight catenary curve between the vertical stabilizer and the fuselage attachment point.
Example Sentence 2
During the banner tow, the cable settled into its natural catenary curve behind the aircraft.