NAVWEPS OD-8OT-80  APPLICATION OF AERODYNAMICS  TO SPECIFIC PROBLEMS OF FLYfNG  an increase in lift coeflicient and reduction in  thrust required. Hence, a “floating”  sensa-  tion may be experienced. Because of the re-  duced drag and power-off deceleration in  ground effect, any excess  speed at the point of  flare may incur a considerable “float”  distance.  As the airplane nears the point of touchdown  on the approach, ground effect will  be most  realized at altitudes less than the wing span.  An exact appreciation of the ground effect may  be obtained during a PcZd approach with the  mirror landing system furnishing an exact  reference  of the flight path.  During the final  phases of the field approach as the airplane  nears the ground plane, a reduced power  setting is necessary  or the reduced thrust re-  quired would allow the airplane to climb  above the desired glide path.  During ship-  board operations, ground effect will be delayed  until the airplane passes  the edge of the deck  and the reduction in power setting that is  common to field operations should not be  encountered. Thus, a habit pattern should  not be formed during field landings which  would prove dangerous during carrier oper-  ations.  moment, and (4) usually a reduction in static  source pressure and increase in indicated air-  speed. These general effects should point out  the possible danger in attempting takeoff  prior to achieving the recommended takeoff  speed. Due to the reduced drag in ground  effect the airplane may seem  capable of takeoff  below the recommended speed. However, as  the airplane rises out of ground effect with a  deficiency of speed, the greater induced drag  may produce marginal initial climb perform-  ance. In the extreme conditions such as high  gross weight, high density altitude, and high  temperature, a deficiency of airspeed at takeoff  may permit the airplane to become airborne  but be incapable of flying ’ out of ground effect.  In this case, the airplane may become airborne  initially with a deficiency of speed, but later  settle back to the runway.  It is imperative  that no attempt be made to force the airplane  to become airborne with a deficiency of speed;  the recommended takeoff speed is necessary  to  provide adequate initial  climb performance.  In fact, ground effect can be used to advantage  if no obstacles exist by using the reduced drag  to improve initial acceleration.  An additional factor to consider is the aero-  dynamic drag of the airplane during the land-  ing roll.  Because  of the reduced induced drag  when in ground effect, aerodynamic braking  will  be of greatest significance only when  partial stalling of the wing can be accom-  plished.  The reduced drag when in ground  effect accounts for the fact that the brakes  are the most effective source of deceleration  for the majority of airplane configurations.  The results of the airplane leaving ground  effect can be most easily realized during the  deck launch of a heavily loaded airplane. As  the airplane moves forward and passes  over the  edge of the deck, whatever ground effect exists  will be lost immediately.  Thus, proper rota-  tion of the airplane will be necessary  to main-  tain the same lift coefficient and the increase  in induced drag must be expected.  The rotor of the helicopter experiences a  similar restraint of induced flow when in prox-  imity to the ground plane. Since the induced  rotor power required will predominate at low  flight speeds,  ground effect will produce a con-  siderable effect on the power required at low  speeds. During hovering and flight at low  speeds, the elevation of the rotor above the  ground plane will be an important factor de-  termining the power required for flight.  During the takeoff pharc of flight ground  effect produces some important relationships.  Of course, the airplane leaving ground effect  encounters just the reverse of the airplane  entering ground effect, i.e., the airplane leaving  ground effect will (1) require an increase in  angle of attack to maintain the same lift  coefficient, (2) experience an increase in in-  duced drag and thrust required, (3) experience  a  decrease  in stability and a nose-up change in  3882 