Definition
A straight reference line drawn from the leading edge to the trailing edge of an airfoil, representing the average chord of the wing. It is used as the baseline from which angle of attack and other aerodynamic angles are measured.
Plain English
An imaginary straight line running from the front edge of the wing to the back edge. It represents the wing's average shape and is used as a reference for measuring how the wing meets the oncoming air.
Context Anchor
Seen in wing diagrams and aerodynamics explanations, especially when showing angle of attack, angle of incidence, and relative wind.
Derivation
Mean' here means 'average,' not 'unkind.' 'Chord' comes from the Latin chorda, meaning 'string' — like the straight string of a bow. So a chord line is the straight line across the curve of the wing, and the mean chord line is the average of those lines across the whole wing.
Why Pilots Care
Angle of attack — one of the most important concepts in flying — is measured between the mean chord line and the relative wind. Understanding this reference line is essential to understanding lift, stalls, and wing performance.
Analogy
Think of drawing one straight centerline through a slightly curved object so you have a simple line to measure from. The real wing has shape, but the mean chord line gives you a clean reference.
Intuition Check
Mean does not mean unkind here; it means average or middle. Chord does not mean a musical sound here; it means a straight reference line between two points on the wing shape.
Example Sentence 1
The angle of attack is the angle between the mean chord line and the relative wind striking the wing.
Example Sentence 2
Aerodynamic moments are calculated using the length of the mean chord line as the reference distance.