text: The effect of free stream density and velocity 
  is a necessary consideration when studying the 
  development of the various aerodynamic forces. 
  Suppose that a particular shape of airfoil 
  is 
  fixed at a particular angle to the airstream. 
  The relative velocity and pressure distribution 
  will be determined by the shape of the airfoil 
  and the angle to the airstream. The effect of 
  varying the airfoil size, air density and air- 
  speed is shown in figure 1.9. 
  If the same air- 
  foil shape is placed at the same angle to an 
  airstream with 
  twice as great a dynamic pres- 
  sure the magnitude of the pressure distribution 
  will be twice as great but the r&rive shape of 
  the pressure distribution will be the same. 
  With 
  twice as great a pressure existing over 
  the surface, all aerodynamic forces and mo- 
  ib 
  ments will ~double. If a half-size airfoil 
  placed at the same angle to the original air- 
  stream, the magnitude of the pressure distri- 
  bution is the same as the origina! airfoi! and 
  again the relative shape of the pressure dis- 
  tribution 
  is identical. The same pressure act- 
  ing on the half-size surface would reduce all 
  aerodynamic forces to one-half that of the 
  original. This similarity of 
  flow patterns 
  means that the stagnation point occurs at the 
  same place, the peak suction pressure occurs 
  at the same place, and the actual magnitude of 
  the aerodynamic forces and moments depends 
  upon the airstream dynamic pressure and the 
  surface area. This concept is extremely im- 
  portant when attempting to separate and ana- 
  lyze the most important factors affecting the 
  development of aerodynamic forces. 