Xem Studiomeasured geometry

Library › Aircraft design › Ground-effect design ·

Ground effect: height/span ratio and induced-drag reduction

How close to the ground does a wing need to be for ground effect? · Standard part · basis: Design rules and figures from the cited sources; example geometry by Xem Studio

Also called: ground effect, ground effect height, ground effect induced drag, wing in ground effect height, ground effect wingspan rule, wieselsberger ground effect, ground effect percentage, how high is ground effect, h/b ground effect, ground effect rc

Exact dimensions. True size, with no printing tolerance added.

sizes
6 in table

Notes

  • Near the ground the wingtip vortices and downwash are suppressed, cutting induced drag. At constant CL the reduction is about 1.4% at one span height, 23.5% at a quarter span and 47.6% at a tenth of a span (FAA-handbook values as reproduced by The Wise Pilot).
  • NASA's tests of low-AR wings found Wieselsberger's h/b theory agreed with experiment for h/b of about 0.03-0.25, but underestimated the benefit below 0.03; the percentage gain in L/D at a given height is the same regardless of aspect ratio (NASA TN D-926).
  • Lift-curve slope also rises near the ground while lift at 0 deg stays nearly constant; at h/c = 1 the wings were essentially out of ground influence (NASA TN D-926).
  • The file is a reference example built by Xem Studio from the numbers above. Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

Ground effect: height/span ratio and induced-drag reduction size chart

parametervalue or rangesource
Induced drag reduction, h = 1 spanabout 1.4%The Wise Pilot (FAA values)
Induced drag reduction, h = 1/4 spanabout 23.5%The Wise Pilot (FAA values)
Induced drag reduction, h = 1/10 spanabout 47.6%The Wise Pilot (FAA values)
Wieselsberger theory valid range (tests)h/b ~0.03-0.25NASA TN D-926
Out of ground influence (chord basis)h/c = 1NASA TN D-926
Reference buildspan 600, chord 300 (AR 2) endplatedcomputed

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

The Wise Pilot (pilot training page; values match FAA PHAK ground-effect figure)Ground EffectwebPublisher's page; dimensions are facts
NASA Langley (Fink & Lastinger)Aerodynamic Characteristics of Low-Aspect-Ratio Wings in Close Proximity to the Ground, NASA TN D-926 (1961)webPublisher's page; dimensions are facts

Free files

★ Free files 1 parts. Xem Studio design: free to use, print and sell things from; not to be republished as files. Xem Studio Design License. index.json

ground-effect-height-span-ratio-wingendplated wing: span 600, chord 300 mm, anhedral 0°, endplates 30 mm (scale to your craft)STEP · STL
Let your AI pull this. Add https://xemstudio.com/mcp to Claude, ChatGPT, Cursor or any MCP client (free, no account, one minute) and it can look up exact sizes, mating fits and free STEP/STL from every chat.
Set it up →

Plain text: sheet.txt · JSON: /api/geometry?object=ground-effect-height-span-ratio

Ground effect: height/span ratio and induced-drag reduction, isometric render of a generated part
Render of ground-effect-height-span-ratio-wing from the free STEP; not to scale.

Fits with

Ground effect: height/chord ratio (ram / chord-dominated regime), isometric render of a generated part
Ground effect: height/chord ratio (ram / chord-dominated regime)7 sizes★ 1 file
Lippisch reverse-delta ground-effect craft, isometric render of a generated part
Lippisch reverse-delta ground-effect craft7 sizes★ 1 file
Ekranoplan layout (low wing + high tailplane out of ground effect), isometric render of a generated part
Ekranoplan layout (low wing + high tailplane out of ground effect)6 sizes★ 1 file
Tandem-wing ground-effect craft (Jorg type), isometric render of a generated part
Tandem-wing ground-effect craft (Jorg type)3 sizes★ 1 file
Power-augmented ram (PAR), isometric render of a generated part
Power-augmented ram (PAR)8 sizes★ 1 file
Endplates on ground-effect wings, isometric render of a generated part
Endplates on ground-effect wings3 sizes★ 1 file

Questions

When does ground effect start?

It is small (about 1.4% induced-drag cut) at one span and strong (47.6%) at a tenth span (FAA values via The Wise Pilot).