text: When the flaps are lowered for landing essen- 
  tially the same items must be considered. Ex- 
  tending the flaps will cause these. changes to 
  take place: 
  
  (1) Lowering 
  
  the flaps requires retrim- 
  to balance the nose down moment 
  
  ming 
  change. 
  
  (2) The increase in drag requires a higher 
  power setting to maintain airspeed and 
  altitude. 
  
  (3) The angle of attack required to pro- 
  duce the same lift coefficient is less, e.g., 
  flap extension tends to cause the airplane to 
  “balloon.” 
  An additional factor which must be consid- 
  ered when rapidly accelerating after takeoff, 
  or when lowering the flaps for landing, is the 
  limit airspeed for 
  flap extension. Excessive 
  airspeeds in the flap down configuration may 
  cause structural damage. 
  
  In many aircraft the effect of intermediate 
  flap deflection is of primary 
  importance in 
  certain critical operating conditions. Small 
  initial deflections of the flap cause noticeable 
  changes in C’s,, without 
  large changes in drag 
  coefficient. This feature is especially true of 
  the airplane equipped with slotted or Fowler 
  flaps (refer to fig. 1.17). Large flap deflections 
  past 30’ 
  to 33’ do not create the same rate of 
  change of Cs- but do cause greater changes in 
  CD. A fact true of most airplanes is that the 
  first 50 percent of flap deflection causes mwc 
  than half of the total change in Cr.- and the 
  last 50 percent of flap deflection causes mo~c 
  than half of the total change in Cs. 