text: be appreciated. The general effect of altitude 
  is expressed by: 
  
  impression of the “barn door” size. Hence, 
  parasite drag can be appreciated as the result 
  of the dynamic pressure, 4, acting on the 
  equivalent parasite area, j. The “equivalent” 
  parasite area is defmed by this relationship as 
  a hypothetical surface with a C,=l.O which 
  produces the same parasite drag as the air- 
  plane. An analogy would be a barn door in 
  the airstream which is equivalent to the air- 
  plane. Typical values for the equivalent para- 
  site area range from 4 sq. ft. for a clean fighter 
  type airplane to 40 sq. ft. for a large transport 
  type airplane. Of course, when any airplane 
  is changed from the clean configuration to the 
  landing configuration, the equivalent parasite 
  area increases. 
  
  EFFECT OF CONFIGURATION. 
  
  The par- 
  is unaffected by lift, but is 
  asite drag, D,, 
  variable with dynamic pressure and equivalent 
  furnishes the 
  parasite area. This principle 
  basis for illustrating 
  the variation of parasite 
  drag with 
  the various conditions of flight. 
  If all other factors are held constant, the para- 
  the equivalent 
  site drag varies directly with 
  parasite area. 