text: the 
  airfoil section, a certain angle must exist be- 
  tween the airfoil chord line and the avcragc 
  relative wind. This angle of attack is a,,, the 
  section angle of attack. However, as this lift 
  is developed on the wing, downwash is in- 
  is in- 
  curred and the average relative wind 
  clined. Thus, the wing must be given some 
  angle attack greater than the required section 
  angle of attack to account for the inclination of 
  the average relative wind. Since the wing 
  must be given this additional angle of attack 
  because of the induced flow, the angle between 
  the average reiative wind arid tlie remote fiCC 
  stream is termed the induced angle of attack, 
  ai. From this influence, the wing angle of 
  attack is the sum of the section and induced 
  angles of attack. 
  
  The effect of the vertical velocities in the 
  vicinity of the wing is best appreciated when 
  they are added vectorially 
  to the airstream 
  velocity. The remote free stream well ahead 
  of the wing is unaffected and its direction is 
  opposite the flight path of the airplane. ‘Aft 
  of the wing, the vertical velocity (2~) adds to 
  the airstream velocity to produce the down- 
  wash angle e (epsilon). At the aerodynamic 
  center of the wing, 
  (w) 
  adds to the airstream velocity to produce a 
  downward deflection of the airstream one-half 
  In other words, 
  that of the downwash angle. 
  the wing producing lift by the deflection of an 
  airstream incurs a downward slant co the wind 
  in the immediate vicinity of the wing. Hence, 
  the JeCtionJ of the wing operate in an average rela- 
  tive wind which is inclined downward one-half the 
  final dowraw& angle. This is one important 
  feature which distinguishes the aerodynamic 
  properties of a wing from 
  the aerodynamic 
  properties of an airfoil section. 
  
  a=ul)+a; 
  a= wing angle of attack 
  OLD= section angle of attack 
  OI;= induced angle of attack 