text: The final chart of figure 4.22 illustrates the 
  fact that the instantaneous slope of the curve of 
  C,, versus @ will describe the static directional 
  stability of the airplane. At small angles of 
  sideslip a strong positive slope depicts strong 
  directional stability. 
  Large angles of sideslip 
  produce zero slope and neutral stability. At 
  very high sideslip the negative slope of the 
  This 
  curve indicates directional 
  decay of directional stability with 
  increased 
  sideslip is not an unusual condition. However, 
  directional instability should not occur at the 
  angles of sideslip of ordinary flight conditions. 
  
  instability. 