What best describes the cause of induced drag?

• A. Wingtip vortices created by lift
• B. Friction drag along the surface
• C. Turbulence from engine exhaust
• D. Boundary layer separation at the tips

Answer: (A)

Induced drag comes from the lift-producing airflow around a finite wing. As the wing creates lift, air tends to spill from the high-pressure area below the wing to the low-pressure area above it at the wingtips, forming wingtip vortices. These swirling vortices generate a downward component of the airflow (downwash) behind the wing. To keep producing the same lift in the presence of this downwash, the wing effectively must work at a higher angle to the oncoming air, which increases drag. So the energy put into creating and maintaining those vortices shows up as induced drag.

That’s why wingtip vortices created by lift are the correct description. Other choices describe different forms of drag (such as surface friction) or phenomena not primarily responsible for the lift-related drag, and don’t capture the mechanism of induced drag.