Definition
An imaginary reference line that runs parallel to the chord of a rotor blade, extending from the blade root outward toward the tip. On a semi-rigid rotor system, the rotor head is free to rock about this axis, allowing the blades to flap as a unit — one blade rising while the opposite blade descends.
Plain English
A line that runs along the length of a rotor blade, in the same direction as the blade itself. On some helicopter rotor systems, the rotor head can tilt back and forth around this line so the blades can move up and down.
Context Anchor
Seen in aerodynamics, aircraft structures, and rotor or propeller blade discussions when describing directions, loads, or measurements on a wing or blade.
Derivation
Chord, from the Latin 'chorda' meaning string or cord, is the straight line from the leading edge to the trailing edge of an airfoil. 'Chordwise' means running in the direction of the chord — that is, along the length of the blade. Knowing this anchors the term to a clear physical line on the blade itself.
Why Pilots Care
Loads and bending along this axis affect wing and blade strength, so designers and maintainers check it to prevent structural issues.
Intuition Check
Do not read chord as a musical chord here. In aviation, the chord is the front-to-back line across a wing or blade section.
Example Sentence 1
On a two-blade semi-rigid rotor, the head teeters about the chordwise axis, letting one blade rise as the other falls.
Example Sentence 2
Engineers measure bending forces along both the chordwise axis and the length of the wing.