text: (5) The thickness and thickness distribu- 
  tion of the profile are important properties 
  of a section. The maximum tbicknus and 
  location of maximum thickness define thick- 
  ness and distribution of thickness and are 
  expressed as fractions or percent of the chord. 
  low speed airfoil may have a. 
  A 
  maximum thickness of 12 percent located 
  30 percent aft of the leading edge. 
  
  typical 
  
  (6) The leading edge radius of the airfoil is 
  the radius of curvature given the leading edge 
  shape. It is the radius of the circle centered 
  on a line tangent to the leading edge camber 
  and connecting tangency pcints of upper and 
  lower surfaces with the leading edge. Typi- 
  cal leading edge radii are zero (knife edge) 
  to 1 or 2 percent. 
  
  (7) The Iift produced by an airfoil 
  
  is the 
  net force produced perpendicular to the n&a- 
  tive wind. 
  
  is the 
  net force produced parallel to the relative wind. 
  (9) The angle of attack is the angle between 
  the chord line and the relative wind. Angle 
  of attack is given the shorthand notation 
  a (alpha). Of course, it is important to dif- 
  i ferentiate between pitch attitude angle and 
  
  (8) The drag incurred by an airfoil 