NAVWEPS OD-BOT-80  APP,LlCATlON OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYING  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.  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.  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.  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-  speed  above stall and turbulence, gusts, turning  flight could produce incipient or con plete  stalling of the airplane.  The increase in drag during takeoff roll due  to frost or ice is not considerable and there  will not be any significant effect on the initial  acceleration during takeoff. Thus, the effect  of frost or ice will be most apparent during the  The general effects  of ice and frost formation  375 