text: Center of gravity position has a relatively 
  negligible effect on static directional stability. 
  The usual range of c.g. position on any air- 
  plane is set by the Jinits of long&d&a/ stability 
  and control. Within 
  range of 
  c.g. position, no significant changes take place 
  in the contribution of the vertical tail, fuselage, 
  nacelles, etc. Hence, the static directional 
  stability is essentially unaffected by the varia- 
  the longitudinal 
  tion of c.g. position within 
  limits. 
  
  this limiting 
  
  When the airplane is at a high angle of a$tack 
  a decrease in static directional stability can be 
  anticipated. As shown by the second chart of 
  figure 4.24, a high angle of attack reduces the 
  stable slope of the curve of C,, versus 8, The 
  decrease in static directional stability is due in 
  great part to the reduction in the contribution 
  of the vertica1 tail. At high angles of attack, 
  the effectiveness of the vertical tail is reduced  the air- 
  plane must have adequate directional control 
  to coordinate turns, balance power effects, 
  create sideslip, balance unsymmetrical power, 
  etc. The principal source of directional con- 
  is the rudder and the rudder must be 
  trol 