Where are vortex generators placed on the wing to minimize high speed drag separation?

• A. Upper surface of wing
• B. Lower surface
• C. Leading edge
• D. Trailing edge

Answer: (A)

Vortex generators work by energizing the boundary layer: they create small, controlled vortices that mix high-energy air from outside the boundary layer into the near-wall region. This keeps the boundary layer momentum higher and helps it stay attached longer in adverse pressure gradients, which reduces drag from flow separation.

Placing them on the upper surface targets the region where separation is most likely during normal flight. Energizing the upper-surface boundary layer delays separation there, lowering drag and maintaining lift. On the lower surface, separation is less of a risk, so the effect would be minimal. Installing them at the leading edge would interfere with the incoming flow and add drag, while placing them too far aft (trailing edge) wouldn’t prevent separation effectively. So the upper surface is the most effective location.