text: flaps are fully extended, and power is set at 
  the 
  idle. This configuration will provide 
  most stable condition which is most demand- 
  ing of controllability. 
  The full deflection of 
  flaps usually provides the greatest wing diving 
  moment and idle power will produce the most 
  critical (least) dynamic pressure at the hoti- 
  zontal tail. 
  
  The landing control requirement has one 
  the maneuvering 
  particular difference from 
  control 
  requirement of free flight. As the 
  airplane approaches the ground surface, there 
  will be a change in the three-dimensional flow 
  of the airplane due to ground effect. A wing in 
  proximity 
  to the ground plane will experience 
  a decrease in tip vortices and downwash at 
  a given lift coefficient. The decrease in down- 
  wash at the tail 
  tends to increase the static 
  stability and produce a nosedown moment from 
  the reduction in download on the tail. Thus, 
  the airplane just off the runway surface will 
  requite additional control deflection to trim 
  at a given lift coefficient and the landing con- 
  trol requirement may be critical in the design 
  of longitudinal control power. 
  
  As an example of ground effect, a typical 
  propeller powered airplane may requite as 
  much as 15” more up elevator to trim at CL- 
  in ground effect than in free flight away from 
  the ground plane. Because of this effect, many 
  aitplaneshavesufIicientcontrolpowertoachieve 
  full stall out of ground effect but do not have 
  to achieve full stall when in close 
  the ability 
  to the ground. 
  proximity 