text: DRAG CHARACTERISTICS. Drag is the 
  net aerodynamic force parallel to the relative 
  wind and its source is the pressure distribution 
  and skin friction on the surface. Large, thick 
  bluff bodies in an airstream show a predomi- 
  nance of form drag due to the unbalanced pres- 
  sure 
  streamlined 
  bodies with smooth contours show a ptedomi- 
  nance of drag due to skin 
  In a 
  fashion similar to other aerodynamic forces, 
  drag forces may be considered in the form of a 
  coefficient which 
  is independent of dynamic 
  pressure and surface area. The basic drag 
  equation is as follows: 
  
  distribution. However, 
  
  The 12-percent section has a cr- 
  approxi- 
  mately 70 percent greater than the 6-percent 
  thick section. 
  In addition, the thicker airfoils 
  have greater benefit from the use of various 
  high lift devices. 
  D=GqS 
  
  The effect of camber is illustrated by the lift 
  curves of the NACA 4412 and 631-412 sections. 
  The NACA 4412 section is a 12 percent thick 
  airfoil which has 4 percent maximum camber 
  located at 40 percent of 
  the chord. The 
  NACA 63i-412 airfoil has the same thickness 
  and thickness distribution as the 631-012 but 
  lift coefficient 
  camber added to give a “design”’ 
  (c, for minimum section drag) of 0.4. The 
  lift curves for these two airfoils show that 
  camber has a beneficial e&t 
  
  where 
  
  D=drag, 
  C,= drag coefficient 
  
  lbs. 
  
  q= dynamic pressure, psf 
  
  UP 
  =z  (V in knots, TAS) 