Span (or wingspan) is the distance from one wingtip to the other, measured perpendicular to the aircraft’s longitudinal axis. Together with chord, it defines the wing planform area (S ≈ span × mean chord) and aspect ratio (AR = span² / S).
Span is the most structurally consequential dimension of a wing. Bending moment at the root scales with span squared (for a given wing loading), meaning that doubling the span quadruples the root bending load. This is why high-span wings require heavy, stiff spars — and why expendable airframes favor short spans that reduce structural requirements at the cost of aerodynamic efficiency.
Span also determines induced drag: longer spans produce weaker tip vortices for a given amount of lift, reducing the energy lost to the wake. This is the fundamental reason that high-endurance UAVs (MQ-9 Reaper: 20 m span; RQ-4 Global Hawk: 40 m span) use long, narrow wings.
Practical span limits for UAVs include: build volume of 3D printers or foam-cutting equipment, vehicle transport width, launch rail or catapult dimensions, and storage container size. Many UAV designs use folding or detachable wings to decouple flight span from transport span.
Related terms
- Chord — the perpendicular wing dimension
- Aspect Ratio — span divided by mean chord, the ratio governing the efficiency-structure trade-off