text: PARASITE DRAG 
  
  In addition to the drag caused by the de- 
  velopment of lift (induced drag) there is the 
  obvious drag which is nor due to the develop 
  ment of lift. A wing surface even at zero lift 
  will have “profile” 
  drag due to skin friction 
  and form. The other components of the air- 
  plane such as the fuselage, tail, nacelles, etc., 
  contribute to drag because of their own form 
  and skin friction. Any loss of momentum of 
  the airstream due to powerplant cooling, air 
  conditioning, or leakage through construction 
  or access gaps is, in effect, an additional drag. 
  When the various components of the airplane 
  are put together the total drag will be greater 
  than the sum of the individual components 
  because of “interference” of one surface on the 
  other. 
  
  From inspection of figure 1.34 it is seen that 
  both CD, and CD, vary with 
  lift coefticient. 
  However, the usual variation of parasite drag 
  allows a simple correlation with 
  the induced 
  In effect, the part of parasite drag 
  drag term. 
  above the minimum at zero lift can be “lumped”  The most usual interference of importance 
  occurs at the wing-body intersection where the 
  growth of boundary layer on the fuselage re- 
  duces the boundary layer velocities on the wing 
  root surface. This reduction in energy allows 