text: have a stable rudder pedal feel through 
  available range of sideslip. 
  
  the 
  
  CONTROL REQUIRE- 
  MENTS. The control power of the rudder 
  must be adequate to contend with 
  the many 
  unsymmetrical conditions of flight. Gener- 
  ally, there are five conditions of flight which 
  provide the most criticalrequirements of di- 
  ‘rectional control power. The type and mission 
  of the airplane will decide which of these 
  conditions is most important. 
  
  DIRECTIONAL 
  
  The effect of rudder deflection is to produce 
  a yawing moment coefficient according to 
  control deflection and produce equilibrium at 
  some angle of sideslip. For small deflections 
  of the rudder, there is no change in stability 
  but a change in equilibrium. 
  Figure 4.25 
  shows the effect of rudder deflection on yawing 
  the change in 
  moment coefficient curves with 
  equilibrium sideslip angle. 
  
  ADVERSE YAW. When an airplane 
  is 
  rolled into a turn yawing moments are pro- 
  duced which require rudder deflection to main- 
  tain zero sideslip, i.e., coordinate the turn. 
  The usual source of adverse yawing moment is 
  illustrated 
  in figure 4.26. When the airplane 
  shown is subject to a roll to the left, the down- 
  going port wing will experience a new relative 
  wind and an increase in angle of attack. The 
  inclination of the lift vector produces a com- 
  ponent force forward on the downgoing wing. 
  The upgoing starboard wing has its lift 
  in- 
  clined with a component force aft. The re- 
  sulting yawing moment due to rolling motion 
  is in a direction opposite to the roll and is 
  The yaw due to roll is 
  hence “adverse yaw.” 
  primarily a function of the wing lift coefficient 
  and is greatest at high C,. 
  
  If 