text: B of figure 4.5 provides comparison of the 
  stable and unstable conditions. Positive sta- 
  is indicated by the curve with negative 
  bility 
  slope. Neutral static stability would be the 
  result if the curve had zero slope. 
  If neutral 
  stability exists, the airplane could be dis- 
  turbed to some higher or lower lift coefficient 
  without change in pitching moment coefficient. 
  Such a condition would indicate that the air- 
  plane would have no tendency to return to 
  some original equilibrium and would not hold 
  trim. An airplane which demonstrates a posi- 
  tive slope of the C, versus C, curve would be 
  unstable. If the unstable airplane were subject 
  to any disturbance from equilibrium at the 
  trim point, the changes in pitching moment 
  would only magnify the disturbance. When 
  the unstable airplane is disturbed to some 
  higher CL, a positive change in C, occurs which 
  would 
  illustrate a tendency for continued, 
  greater displacement. When the unstable air- 
  plane is disturbed to some lower C,,, a negative 
  change in C, takes place which tends to create 
  continued displacement. 
  
  The pitching moment coefficients contributed 
  by all the various components of the aircraft 
  are summed up and plotted versus lift coeffi- 
  cient. Study of this plot of C, versus C, 
  will 
  stability 
  of the airplane. 
  
  relate the static  longitudinal 