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 
27