text: The choice of an airfoil section will depend 
  on the consideration oftmany different factors. 
  While the cI, of the section is an important 
  quality, a more appropriate factor for con- 
  sideration is the maximum lift coefficient of 
  the section when various high lift devices are 
  applied. Trailing edge flaps and leading edge 
  high lift devices are applied to increase the 
  for low speed performance. Thus, an 
  cr,, 
  appropriate factor for comparison is the ratio 
  of section drag coe5cient to section maximum 
  flaps-cd/crm,. When this 
  lift coefficient with 
  quantity 
  is corrected for compressibility, a 
  preliminary selection of an airfoil section is 
  possible. The airfoil having the lowest value 
  of c&~, at the design flight condition (en- 
  durance, range, high speed, etc.) will create 
  the least section drag for a given .design stall 
  speed. 