text: percent and, when the wing 
  equal to one-tenth the span (h/b=O.l), 
  reduction 
  Thus, a large reduction in induced drag will 
  take place only when the wing is very close 
  to 
  the ground. Because of this variation, 
  ground effect is most usually recognized during 
  the liftoff of takeoff or prior to touchdown on 
  landing. 
  
  is at a height 
  the 
  induced drag is 47.6 percent.  in 
  
  The reduction of the tip or trailing vortices 
  due to ground effect alters the spanwise lift 
  distribution and reduces the induced angle of 
  require 
  In this case, the wing will 
  attack. 
  a lower angle of attack in ground effect to 
  produce the same lift coefficient. This effect 
  is illustrated by the lift curves of figure 6.9 
  which show that the airplane in ground effect 
  will develop a greater slope of the lift curve. 
  For the wing in ground effect, a lower angle of 
  attack is necessary to produce the same lift 
  coefficient or, if a constant angle of attack is 
  maintained, an increase in lift coefficient will 
  result. 
  
  Figure 6.9 illustrates the manner in which 
  ground effect will alter the curve of thrust re- 
  quired versus velocity. Since induced drag 
  predominates at low speeds, the reduction of 
  induced drag due to ground effect will cause 
  the most significant reduction of thrust re- 
  quired (parasite plus induced drag) only at 
  low speeds. At high speeds where parasite 
  drag predominates, the induced drag is but 
  a small part of the total drag and ground 
  effect causes no significant change in thrust re- 
  quired. Because ground effect involves the 
  induced effects of airplane when in close prox- 
  imity to the ground, its effects are of greatest 
  concern during the takeoff and landing. Ordi- 
  narily, 
  in 
  which the airplane would be in close proximity 
  to the ground. 
  
  these are the only phases of flight 