text: Ordinarily,  the static longitudinal stability 
  
  of a conventional airplane configuration does 
  In other words, 
  not vary with lift coefficient. 
  the slope of C, versus CL does not change with 
  CL. However, if the airplane has sweepback, 
  large contribution of power effects to stability, 
  or significant changes in downwash at the 
  tail, noticeable changes in static 
  horizontal 
  stability can occur at high 
  lift coefficients. 
  This condition 
  is illustrated by graph C of 
  figure 4.5. The curve of C, versus CL of this 
  illustration shows a good stable slope at low 
  values of CL. Increasing CL effects a slight 
  decrease in the negative slope hence a decrease 
  in stability occurs. With continued increase 
  in C,, the slope becomes zero and neutral 
  stability exists. Eventually, 
  the slope be- 
  comes positive and the airplane becomes un- 
  stable or “pitch-up” 
  results. Thus, at any 
  lift coefficient, the static stability of the air- 
  pl.ane is depicted by the slope of the curve of 
  CM versus CL. 