text: (2) The chord is the characteristic dimen- 
  
  sion of the airfoil. 
  
  (3) The mean-camber line is a line drawn 
  halfway between the upper and lower sur- 
  faces. Actually, the chord line connects the 
  ends of the mean-camber line. 
  
  (4) The shape of the mean-camber line is 
  very important 
  in determining the aerody- 
  namic characteristics of an airfoil section. 
  The maximum camber (displacement of the 
  mean line from the chord line) and the Ioca- 
  tion of the maximum camber help to define 
  the shape of the mean-camber line. These 
  quantities are expressed as fractions or per- 
  cent of the basic chord dimension. A typi- 
  cal iow speed airfoil may have a maximum 
  camber of 4 percent located 40 percent aft of 
  the leading edge. 
  
  the description of an airfoil 
  profile is by dimensions which are fractions or 
  percent of the basic chord dimension. Thus, 
  when an airfoil. profile is specified a relative 
  shape is described. (NOTB: A numerical sys- 
  tem of designating airfoil profiles originated 
  by the National ~Advisory Committee for Aero- 
  nautics [NACA] 
  is used to describe the main 
  geometric features and certain aerodynamic 
  properties. NACA Report Nol 824 wi!! pro- 
  vide the detail of this system.) 