(2) Plane of transition,  BO,  figure 17, is oblique with regard to the  .  .  aX;J.S.  (1) Positive pressure on the nose lies almost entirely in a zone be› neath the axis.  c.  Figure 17 shows the distributions in pressure for an 18° angle  of attack to the relative air.  Other angles of attack have similar dis› tributions.  The distribution shown holds equally true whether the  deviation of the axis from the direction of motion is in a horizontal  or a vertical plane. When, for instance, the inclination is in the verti› cal plane, the following chara_cteristics are observed:  {3) Both nose and tail have positive pressure, but that on the tail  is too small to be of much assistance to forward motion.  (2) Varying reduced pressure exists from a section just in rear of  the nose to a section just forward of the tail.  ( 1) Distribution depicted is uniform for any plane passed through  ~  the longitudinal axis.  pa.rallel with the direction of motion.  Because an airship can be  con~ .  sidered as a symmetrical solid of revolution, the pressure distribnt.ion  has the following charactertistics :  •  FIGURE 16.-Pressure distribution on airship hull (longitudinal arls pa rat:el to direction  •  of motion).  - +  +  Direefion  o!  mofiDfl  22! Variation of pressure distribution on airship hull.--a.  In  section II resistance of an airship was shown to be parfly caused  by increased n<?Se pressure.  Throughout the discussion the airship  was considered to be flying on an even keel and in a straight line ..  All forces were parallel to the direction of flight.  Before entering•  the subject of stability proper it will be necessary  to  show variation  in pressure distribution on the hull when the airship is not flying as  considered in section II, or, in other words, when transverse aero- .  dynamic forces are present on the hull.  b.  Figure 16 shows a typical pressure distribution on an airship hull  when the airship is in horizontal flight in a straight line and on an even  keel.  This pressure distribution will be true whenever the line  join~  ing the tip of the nose with the tip of the tail (longitudinal axis) is  AIR CORPS  TM 1-320  22  36 