Spanwise flow around a wing moves from bottom surface toward the tips in which direction?

• A. From bottom surface toward the tips
• B. From tips toward bottom
• C. From top toward bottom
• D. Circular around

Answer: (A)

Spanwise flow around a finite wing tends to move air along the surface from the root toward the tip. Lift creates a three‑dimensional circulation with downwash at the tip, and the pressure differences along the wing drive air on the lower surface to slide outward toward the tip. This outward movement on the bottom surface contributes to the overall spanwise flow that feeds the wingtip vortex and the induced circulation. So the air flows from the bottom surface toward the tips. It isn’t a flow from tips toward the root, nor a vertical or circular motion around the wing.