text: of such a device. To illustrate a few principles 
  of flap management, figure 1.19 presents the 
  lift and drag curves of a typical airplane in the 
  clean and flap down configurations. 
  
  In order to appreciate some of the factors 
  involved in flap management, assume that the 
  airpIane has just taken off and the flaps are 
  extended. The pilot should not completely 
  retract the flaps until the airplane has sufficient 
  speed. If the flaps are retracted prematurely 
  at insufhcient airspeed, maximum lift coefi- 
  cient of the clean configuration may not be 
  able to support the airplane and the airplane 
  will sink or stall. Of course, this same factor 
  must be considered for intermediate flap posi- 
  tions between fully 
  retracted and fully ex- 
  tended. Assume that the airplane is allowed 
  to gain speed and reduce the flight lift coefii- 
  cient to the point of flap retraction indicated 
  on figure 1.19. As the configuration is altered 
  to the clean configura- 
  from the “cluttered” 
  tion, three important changes take place: 
  
  (1) The reduction in camber by flap re- 
  traction changes the wing pitching moment 
  and-for 
  the majority of airplanes-requires 
  retrimming to balance the nose up moment 
  change. Some airplanes feature an automat- 
  is programmed with 
  ic retrimming which 
  flap deflection. 