text: OF 
  GROUND EFFECT. While the aerodynamic 
  characteristics of the tail and fuselage are 
  altered by ground effects, the principal effects 
  due to proximity of the ground plane are the 
  changes in 
  the aerodynamic characteristics 
  of the wing. As the wing encounters ground 
  effect and is maintained at a constant lift 
  coefficient, there is a reduction in the upwash, 
  downwash, and the tip vortices. These effects 
  are illustrated by the sketches of figure 6.9. 
  As a result of the reduced tip vortices, the wing 
  in the presence of ground effect will behave as 
  if it were of a greater aspect ratio. 
  In other 
  words, the induced velocities due to the tip 
  (or trailing) vortices will be reduced and the 
  wing will 
  incur smaller values of induced 
  drag coefficient, C,<, and induced angle of 
  attack, OL;, for any specific lift coefhcient, C,. 
  In order for ground effect to be of a signifi- 
  cant magnitude, the wing must be quite close 
  to the ground plane. Figure 6.9 illustrates 
  one of the direct results of ground effect by 
  the variation of induced drag coefficient with 
  wing height above the ground plane for a 
  representative unswept wing at constant lift 
  coefficient. Notice 
  the wing must be 
  that 
  quite close to the ground for a noticeable 
  reduction in induced drag. When the wing 
  is at a height equal to the span (h/b=l.O), 
  induced drag is only 1.4 
  the reduction 
  percent. However, when the wing 
  is at a 
  height equal to one-fourth the span (b/b= 
  0.25), 