text: stances, the 4 at the tail is usually less and this 
  reduces the efficiency of the tail. 
  
  When the airplane is given a change in angle 
  of attack, the horizontal 
  tail does not expe- 
  rience the same change in angle of attack as 
  the wing. Because of the increase in down- 
  wash behind, the wing, the horizontal tail will 
  experience a smaller change in angle of attack, 
  e.g., if a 10" change in wing angle of attack 
  causes a 4O increase in downwash at the hori- 
  zontal 
  only a 6’ change in angle of attack. 
  In this 
  manner, the downwash at the horizontal 
  tail 
  reduces the contribution 
  Any 
  factor which alters the rate of change of down- 
  wash at the horizontal tail will directly affect 
  the tail contribution and airplane stability. 
  
  Power effects can alter the downwash at the 
  horizontal tail and affect the tail contribution. 
  Also, the ~downwash at the tail is affected by 
  the lift distribution on the wing and the flow 
  condition ,on the fuselage. The low aspect 
  ratio airplane requires large angles of attack 
  to achieve high ,lift coefficients and this posi- 
  tions the fuselage at high angles of attack. 
  The change in the wing downwash can be 
  accompanied by crossflow separation vortices 
  is possible that the net 
  on the fuselage. 
  effect obviates or destabilizes the contribu- 
  tion of the horizontal 
  tail and produces air- 
  plane instability. 