text: The effect of frost is perhaps more subtle 
  than the effect of ice formation on the aero- 
  dynamic characteristics of the wing. The ac- 
  cumulation of a hard coat of frost on the wing 
  upper surface will provide a surface texture of 
  considerable roughness. While the basic shape 
  and aerodynamic contour is unchanged, the 
  increase in surface roughness increases skin- 
  friction and reduces the kinetic energy of the 
  boundary layer. As a result, there will be an 
  increase in drag but, of course, the magnitude 
  of drag increase will not compare with 
  the 
  considerable increase due to a severe ice forma- 
  tion. The reduction of boundary layer kinetic 
  energy will cause incipient stalling of the wing, 
  i.e., separation will occur at angles of attack 
  and lift coefficients lower than for the clean, 
  smooth wing. While the reduction in C,,,, 
  due to frost formation ordinarily is not as great 
  as that due to ice formation, it is usually un- 
  expected because it may be thought that large 
  changes in the aerodynamic shape (such as 
  due to ice) are necessary to reduce CL,az. How- 
  ever, the kinetic energy of the boundary layer 
  is an important 
  factor influencing separation 
  of the airflow and this energy is reduced by an 
  increase in surface roughness. 