text: CONTROL FORCE STABILITY. The static 
  longitudinal stability of an airplane is defined 
  by the tendency to return to equilibrium upon 
  displacement. 
  the stable air- 
  In otherwords, 
  plane will resist displacement from the trim or 
  equilibrium. 
  The control forces of the air- 
  plane should reflect the stability of the air- 
  plane and provide suitable reference for precise 
  control of the airplane. 
  
  The deflection of the slipstream by the nor- 
  mal force at the propeller tends to increase the 
  downwash at the horizontal 
  tail and reduce 
  the contribution 
  to stability. Essentially the 
  same destabilizing effect is produced by the 
  flow induced at the exhaust of the jet power- 
  plant. Ordinarily, 
  the induced flow at the 
  horizontal tail of a jet airplane is slight and is 
  destabilizing when the jet passes underneath 
  The magnitude of the 
  the horizontal 
  tends to be 
  indirect power effects on stability 
  greatest at high Cr, high power, and low flight 
  speeds. 
  
  The effect of elevator deflection on pitching 
  moments is illustrated by the first graph of 
  figure 4.13. 
  If the elevators of the airplane are 
  fixed at zero deflection, the resulting line of 
  CM versus C’s for 0’ depicts the static stability 
  and trim lift coefficient. 
  If the elevators are 
  fixed at a deflection of 10” up, the airplane 
  is unchanged but the trim lift 
  static stability 
  coefficient is increased. A change in elevator 
  or stabilizer position does not alter the tail 
  contribution 
  to stability but the change in 
  pitching moment will alter the lift coeflicient  The combined direct and indirect power 
  to a general reduction of 