The spanwise air movement along the wing is defined as which of the following?

• A. Spanwise flow toward the tips
• B. Circular flow
• C. Pressure-lift coupling
• D. Normal flow

Answer: (A)

Spanwise flow is air moving along the wing from the root toward the tip. On a finite wing, the pressure differences around the surface create a component of velocity that runs along the span to satisfy the three-dimensional flow around the wing, so the movement is toward the tips. That’s why describing spanwise air movement as toward the tips is the correct choice. The other options don’t match: circular flow would imply rotation around the wing rather than along its length, normal flow is perpendicular to the surface, and pressure-lift coupling refers to how pressure distribution and lift interact rather than a direction of flow. Understanding spanwise flow helps explain stall progression and why designers use washout or winglets to manage it.