Ground effect causes which change to induced drag?

• A. Increase in induced drag
• B. No change
• C. Decrease in induced drag
• D. Variable with speed

Answer: (C)

Ground effect occurs when the aircraft flies close to the surface. The presence of the ground interferes with the wingtip vortices and downwash that build up behind the wing. This interference makes the wing more efficient at producing lift, which means the same amount of lift can be generated with less downward air flow. Since induced drag is produced by that downwash and wingtip vortex strength, reducing the downwash lowers the induced drag for the same lift. This effect is most noticeable within about one wingspan of the surface and fades as you climb higher, where ground effect diminishes. So, ground effect causes a decrease in induced drag.