Why do wing tips generate trailing vortices, and how do they affect induced drag?

Why do wing tips generate trailing vortices, and how do they affect induced drag?

• A. Finite wings create non-uniform lift, producing spanwise vortices that induce downwash, increasing induced drag and reducing lift efficiency near the tips.
• B. Wing tips have no effect on lift or drag.
• C. Vortices at tips only affect high-speed flight.
• D. Induced drag decreases with wing tip vortices.

Answer: (A)

Wing tips generate trailing vortices because a finite wing must create lift with a pressure difference between the lower and upper surfaces, and air leaks around the tips from the high-pressure region beneath the wing to the low-pressure region above it. This cross‑flow curls into the wingtip, producing a pair of counter‑rotating vortices that trails behind the wing. Those tip vortices drive a downward component of flow in the wake, known as downwash. The downwash tilts the wing’s lift vector backward, so part of the lift acts opposite the flight direction. That backward component is induced drag. As the vortices strengthen with lift, the downwash increases, more of the lift is wasted as drag, and the lift efficiency near the tips drops because the local flow is less favorable for producing forward lift. In contrast, an infinite wing (no tips) would have no trailing vortices and negligible induced drag; the finite-span wing inevitably shows this tip effect. While induced drag is especially relevant at low speeds (where higher lift is needed), the basic mechanism—tip vortices creating downwash and rearward lift tilt—is the reason wing tips contribute to induced drag.

Wing tips generate trailing vortices because a finite wing must create lift with a pressure difference between the lower and upper surfaces, and air leaks around the tips from the high-pressure region beneath the wing to the low-pressure region above it. This cross‑flow curls into the wingtip, producing a pair of counter‑rotating vortices that trails behind the wing.

Those tip vortices drive a downward component of flow in the wake, known as downwash. The downwash tilts the wing’s lift vector backward, so part of the lift acts opposite the flight direction. That backward component is induced drag. As the vortices strengthen with lift, the downwash increases, more of the lift is wasted as drag, and the lift efficiency near the tips drops because the local flow is less favorable for producing forward lift.

In contrast, an infinite wing (no tips) would have no trailing vortices and negligible induced drag; the finite-span wing inevitably shows this tip effect. While induced drag is especially relevant at low speeds (where higher lift is needed), the basic mechanism—tip vortices creating downwash and rearward lift tilt—is the reason wing tips contribute to induced drag.