text: AIRFOIL LIFT CHARACTERISTICS. Air- 
  foil section properties differ from wing or 
  airplane properties because of the effect of the 
  planform. Actually, the wing may have vati- 
  ous airfoil sections from root to tip with taper, 
  twist, sweepback and local flow components 
  in a spanwise direction. The resulting aeto- 
  dynamic properties of the wing are determined 
  by the action of each section along the span 
  and the three-dimensional flow. Airfoil sec- 
  tion properties are derived from the basic shape 
  or profile in two-dimensional flow and the force 
  coefficients are given a notation of lower case 
  letters. For example, a wing or airplane lift 
  coefficient is C, while an airfoil section lift 
  coefficient is termed cr. Also, wing angle of 
  attack is Q while section angle of attack is 
  differentiated by the use of 01~. The study of 
  section properties allows an objective consider- 
  ation of the effects of camber, thickness, etc. 
  
  The lift characteristics of five illustrative 
  airfoil sections are shown in figure 1.12. The 
  section lift coe&icient, c,, is plotted versus 
  section angle of attack, olO, for five standard 
  NACA airfoil profiles. One characteristic fea- 
  ture of all airfoil sections is that the slope of 
  the various lift curves is essentially the same. 
  At low lift coefhcients, the section lift coeffi- 
  cient 
  increases approximately 0.1 for each 
  degree increase in angle of attack. For each 
  of the airfoils shown, a S’ change in angle of 