text: POWER EFFECTS. The effects of power may 
  cause significant changes in trim lift coefficient 
  and static. longitudinal stability. 
  Since the 
  is evaluated by the 
  contribution 
  change in moment coefficients, power effects 
  will be most significant when the airplane 
  operates at high power and low airspeeds such 
  as the power approach or waveoff condition. 
  The effects of power are considered in two 
  main categories. First, 
  there are the direct 
  effects resulting from the forces created by the 
  propulsion unit. Next, there are the indirect 
  effects of the slipstream and other associated 
  flow which alter the forces and moments of the 
  aerodynamic surfaces. The direct effects of 
  power are illustrated in figure 4.11. The ver- 
  tical location of the thrust line defines one of 
  If the 
  the direct contributions 
  
  to stability 
  
  POWER-OFF STABILITY. When the in- 
  trinsic stability of a configuration is of interest, 
  power effects are neglected and the stability 
  is considered by a buildup of the contributing~ 
  components. Figure 4.10 illustrates a typical 
  buildup of the components of a conventional 
  airplane configuration. 
  the c.g. is arbi- 
  trarily set at 30 percent MAC, the contribu- 
  tion of the wing alone is destabilizing as indi- 
  cated by the positive slope of CM versus C,. 
  The combination of the wing and fuselage 
  The contribution 
  increases the instability. 
  of the tail alone is highly stabilizing 
  from 
  the large negative slope of the curve. The 
  contribution of the tail must be sufficiently  to stability. 