text: Induced drag predominates at speeds below 
  the point of minimum total drag. When the 
  airplane is operated at the condition of mini- 
  mum power required, the total drag is 75 
  percent induced drag and 25 percent parasite 
  drag. Thus, the induced drag is three times as 
  great as the parasite drag when at minimum 
  power required. 
  
  where 
  
  Va=speed corresponding to the same C, 
  but a different weight, Ws 
  POWER REQUIRED 
  
  For the example airplane of figure 2.2, a change 
  of gross weight from 15,000 to 22,500 lbs. re- 
  quires that the airplane operate at speeds which 
  are 22.5 percent greater to maintain a specific 
  lift coefficient. For example, if the 15,000-lb. 
  airplane operates at 160 knots for (L/D)-, 
  the 
  speed for (L/D)mz at 22,500 lbs. is: 
  
  The curves of thrust required and power 
  required versus velocity provide the basis for 
  comprehensive analysis of all the major items 
  of airplane performance. The changes in the 
  drag and power curves with variations of air-- 
  plane gross weight, configuration, and altitude 
  the ‘variation of range, 
  furnish 
  endurance, climb performance, etc., with these 
  same items. 
  
  insight  for 