Definition
Along the direction of the wingspan — that is, from the wing root (where the wing meets the fuselage) outward toward the wingtip, or from one wingtip across to the other. Used to describe airflow, pressure distribution, structural members, or any movement or measurement that runs across the wing from side to side rather than front to back.
Plain English
Going sideways along the wing, from where it joins the body of the airplane out to the tip — the long direction of the wing.
Context Anchor
Seen in aerodynamic discussions of airflow over the wing, especially when explaining induced drag and wingtip vortices.
Derivation
A combination of 'span' (the full side-to-side length of the wings) and the suffix '-wise' (meaning 'in the direction of'). So spanwise simply means 'in the direction of the span.' Compare with 'chordwise,' which means in the direction of the chord — front to back across the wing.
Why Pilots Care
Spanwise airflow near the tips forms vortices that increase drag and reduce overall lift efficiency.
Intuition Check
Spanwise does not mean any sideways movement anywhere on the airplane. On a wing, it specifically means along the wing’s span, toward or away from the wingtip.
Example Sentence 1
Higher pressure under the wing causes air to flow spanwise toward the wingtip, where it spills over the top and forms a vortex.
Example Sentence 2
Winglets are added to reduce spanwise flow and lower induced drag.