A large formation of ice on the leading edge 
of the wing can produce large changes in the 
local contours and severe local pressure gra- 
dients. The extreme surface roughness common 
to some forms of ice will cause high surface 
friction and a considerable reduction of bound- 
ary layer energy. As a result of these effects, 
the ice formation can produce considerable in- 
crease in drag and a large reduction in maxi- 
mum lift coefficient. Thus, the ice formation 
will cause an increase in power required and 
stall speed. In addition, the added weight of 
the ice formation on the airplane will provide 
an undesirable effect. Because of the detri- 
mental effects of ice formation, recommended 
anti-icing procedures must be followed to 
preserve the airplane performance. 
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. 
The general effects of ice and frost formation 
NAVWEPS OD-BOT-80 
APP,LlCATlON OF AERODYNAMICS 
TO SPECIFIC PROBLEMS OF FLYING 
on the lift characteristics is typified by the il- 
lustration of figure 6.7. 
The effect of ice or frost on takeoff and land- 
ing performance is of great importance. The 
effects are so detrimental to the landing and 
takeoff that no effort should be spared to keep 
the airplane as free as possible from any ac- 
cumulation of ice or frost. If any ice remains 
on the airplane as the landing phase approaches 
it must be appreciated that the ice formation 
will have reduced CL,., and incurred an increase 
in stall speed. Thus, the landing speed will be 
greater. When this effect is coupled with the 
possibility of poor braking action during the 
landing roll, a critical situation can exist. It is 
obvious that .great effort must be made to 
prevent the accumulation of ice during flight. 
In no circumstances should a formation of ice 
or frost be allowed to remain on the airplane 
wing surfaces prior to takeoff. The undesir- 
able effects of ice are obvious but, as previously 
mentioned, the effects of frost are more subtle. 
If a heavy coat of hard frost exists on the wing 
upper surface, a typical reduction in CL,.. 
would cause a 5 to 10 percent increase in the 
airplane stall speed. Because of this magnitude 
of effect, the effect of frost on takeoff per- 
formance may not be realized until too late. 
The takeoff speed of an airplane is generally 
some speed 5 to 25 percent greater than the 
stall speed, hence the takeoff lift coefficient 
will be value from 90 to 65 percent of C1,,.., 
Thus, it is possible that the airplane with frost 
cannot become airborne at the specified take- 
off speed because of premature stalling. Even 
if the airplane with frost were to become air- 
borne at the specified takeoff speed, the air- 
plane could have insufficient margin of air-