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SESK: Stuff Everyone Should Know · sesk.info/comm-ground-effect-induced-drag

A wing at one-tenth of its span above the ground has its induced drag cut by about how much?

About 48 percent, which is why airplanes float before landing.

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  1. About 5 percent
  2. About 48 percent ✔
  3. About 24 percent

Why: The ground interferes with the wingtip vortices and downwash, so induced drag drops. At a height of one-tenth span it falls 47.6 percent. At a full span of height it is only 1.4 percent.

Huh, didn't know that: At one-fourth of the span above the ground the reduction in induced drag is 23.5 percent.

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References

Answer: About 48 percent. The ground interferes with the wingtip vortices and downwash, so induced drag drops. At a height of one-tenth span it falls 47.6 percent. At a full span of height it is only 1.4 percent.

  1. PHAK ch 5, Aerodynamics of Flight (FAA-H-8083-25C) www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf
    reduction in induced drag is 47.6
    Checked 2026-10-11.
  2. PHAK ch 5, Aerodynamics of Flight (FAA-H-8083-25C) www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf
    drag is 23.5 percent
    Checked 2026-10-11.
  3. PHAK ch 5, Aerodynamics of Flight (FAA-H-8083-25C) www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf
    ground effect is most usually recognized during the liftoff for takeoff or just prior to touchdown
    Checked 2026-10-11.

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