text: The effect of reduced stability on .controlla- 
  bility is illustrated by the ball on a flat surface. 
  When neutral static stability exists, the ball 
  may be displaced from equilibrium and there 
  is no stable tendency to return. A new point 
  is obtained and no force is 
  of equilibrium 
  required to maintain 
  the displacement. As 
  the static stability approaches zero, controlla- 
  increases to infinity and the only resist- 
  bility 
  the 
  ance to displacement is a resistance to 
  motion of displacement-damping. 
  For this 
  reason, the lower Limits of stability may be Set 
  by the upper limits of controllability. 
  the 
  stability of the aircraft is too low, control 
  deflections may create exaggerated displace- 
  ments of the aircraft. 
  
  AIRPLANE REFERENCE AXES 
  
  The effect of static instability. on controlla- 
  bility 
  If 
  is illustrated by the ball on a hill. 
  the ball is displaced from equilibrium at the 
  top of the hill, 
  tendency is for the 
  ball td continue in the displaced direction. 
  In order to “control”~the ball to some lateral 
  displacement, a force must be applied oppo& 
  to the direction of displacement. This effect 
  would be appreciated during flight of an un- 
  stable aircraft by an unstable “feel” of the air- 
  the controls were deflected co in- 
  craft. 