TM 1-320  34  AIRSHIP AERODYNAMICS  F IGURE 23.-Actlon of alrsblp in a ,•oid- ing nn obstacle.  FIGURE 22.- rlction of airship In a turn.  airship.  To miss the obstacle t he pilot must first put over the rudder  to deflect the nose of the airship and then completely reverse the  rudder.  In  this case the action is as shown in figure 23.  f.  There is one other situatioll in which the direction pilot must  exercise caution.  As the airship turns under action of the rudder,  centrifugal force acting on the center of gravity  will swing the car  to the outside.  This action will so tilt the hu1l that the rudder will  become  in  part an elevator.  .Air striking on the inside of the rud› der  will depress the nose of the ship.  This depression can be stopped  by prompt application of the elevator controls by the altitude pilot.  However in some cases, especially when near the ground with a heavy  airship, the altitude pilot may  be  unable to. use the elevators without  endangering the tail of the airship.  Hence the ’direction pilot must  .  49  r;  I  I  I  I  1Ye  ’Yr  (I)  ’( Yr  I  I  I  rrr \ ’(’ Y,.  e.  It occasionally happens, especially when flying through foggy  atmosphere, that an obstacle  will suddenly loom up in front of the  the right is  to  shift the airship slightly to the left so that  if  the air- ship were being flown along close to the right side of a wall or other  obstruction, it would not be safe to put the rudder over sharply to the  right in order to turn to the right and get away from the obstruc› tion, as the immediate effect of such an action would be  to  drive the  airship into the wall.  The approximate path of the airship when  the rudder is put over  to  the right, together with several successive  positions of the axis of the airship, are indicated in figure 22. 