NAVWEPS OO-BOT-80  APPLICATION OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYING  When an airplane in flight nears the ground  (or water) surface, a change occurs in the  three dimensional flow pattern because the  local airflow cannot have a vertical component  at the ground plane. Thus, the ground plane  will furnish a restriction to the flow and alter  the wing upwash, downwash, and tip vortices.  These general effects due to the presence of  the ground plane are referred to as “ground  effect.  ‘ *  airspeed will allow.  If full flap deflection is  utilized for takeoff it is important to recall that  the last 50 percent of flap deflection creates  more than half the total drag increase but less  than half the total change in CL,-.  Thus, for  some configurations of airplanes, a greater re-  duction in drag may be accomplished by partial  retraction of the flaps rather than retraction of  the landing gear.  Also,  it is important that no  steep turns be attempted because  of the unde-  sirable increase in induced drag.  GROUND EFFECT  AERODYNAMIC  INFLUENCE  OF  GROUND EFFECT. While the aerodynamic  characteristics of the tail and fuselage are  altered by ground effects, the principal effects  due to proximity of the ground plane are the  changes in the aerodynamic characteristics  of the wing.  As the wing encounters ground  effect and is maintained at a constant lift  coefficient, there is a reduction in the upwash,  downwash, and the tip vortices. These effects  are illustrated by the sketches of figure 6.9.  As a result of the reduced tip vortices, the wing  in the presence  of ground effect will behave as  if it were of a greater aspect ratio.  In other  words, the induced velocities due to the tip  (or trailing) vortices will be reduced and the  wing will  incur smaller values of induced  drag coefficient, C,<, and induced angle of  attack, OL;,  for any specific lift coefhcient, C,.  During the landing with an engine inopera-  tive, the same fundamental precautions must  be observed as during takeoff, i.e., minimum  directional control speed must be maintained  (or exceeded), no steep turns should be at-  tempted, and the extension of the flaps and  landing gear must be well planned. In the case  of ’ a critical power condition it may be neces-  sary to delay the extension of the landing gear  and full flaps until a successful  landing is as-  sured. If a waveoff is necessary,  maximum per-  formance will be obtained cleaning up the air-  plane and accelerating to the best climb speed  before attempting any gain in altitude.  At all times during flight with an engine  inoperative, the pilot must utilize the proper  techniques for control of airspeed and altitude,  e.g., for the conditions of steady flight, angle  of attack is the primary control of airspeed  and excess power is the primary control of  rate of climb. For example, if during approach  to landing the extension of full flaps and  landing gear creates a deficiency of power at  all speeds, the airplane will be committed to  descend. If the approach is not properly  planned and the airplane sinks below the  desired glide path, an increase in angle of  attack will only allow the airplane to fly more  slowly and descend  more rapidly.  An attempt  to hold altitude by increased angle of attack  when a power deficiency exists only causes a  continued loss of airspeed. Proper procedures  and technique are an absolute necessity for  safe flight when an engine failure occurs.  In order for ground effect to be of a signifi-  cant magnitude, the wing must be quite close  to the ground plane.  Figure 6.9 illustrates  one of the direct results of ground effect by  the variation of induced drag coefficient with  wing height above the ground plane for a  representative unswept wing at constant lift  coefficient. Notice that the wing must be  quite close to the ground for a noticeable  reduction in induced drag.  When the wing  is at a height equal to the span (h/b=l.O),  the reduction in induced drag is only 1.4  percent. However, when the wing is at a  height equal to one-fourth the span (b/b=  0.25),  the reduction in induced drag is 23.5  379 