TM 1-320  25-26  AIRSHIP AERODYNAMICS  motions.  With this fact  in  mind the types of stability now will be  considered.  26. Types of  stability.-a. Stability is defined as the tendency  to return  to a position of equilibrium after a small deviation from that  position.  b.  In airships stability is accomplished by two means, static and  dynamic.  (1) Strictly speaking, the only real statical stability is that which  exists when the engines are stopped.  Under this condition an air- ’  FJGtJRE 19.-Cbart showing axes of airship and conventional symbols related thereto.  Axis  3’  Moment about axis  Angle  .  ~  I  0  ~  I ~  0  . ...........  .  ....  ..9l..8  ~  Q  -;s s:l  ~  t:l  Designation  ’"’» 0  0  a!UJ  ....  .,...  - B  ~  .....  Q)  ~  0  g,  0  >  ~  .a  ~  .0  ....  bO  ~  .  s  .....  a  .....  ,..  rJl  ~  tl.l  £  &  Q)  >.  Q)  ~  00  ~  LongitudinaL __ ___  X  X  Rolling ___  L  $^{1 }$Y- -z RolL __  LateraL __ _______ _  y  y  Pitching __  M  z  X  Pitch __  I  NormaL _________  z  Yawing __  N  x--Y Yaw  ___  Velocities  I ,.-...  8.·~  s~  Obi) ~~  .......  0  ~  0  ,..  .....  .a  ala!  ~  Q)~  ~  Q .  bO  ..... Q)  ~  00  H  ~=: ·  4>  u  p  e  v  q  ’1’  w  r  Normt~l  or verlh;;a/  Axis  /  /  \  \  ~ os ifive  Oirecf"itms oF 1’9xe.s and  /l nfJ ~  (Forces ond.moment-.5  .s ~ wn  hit drrow.s)  39  -