42  TM 1-320  27  AIR CORPS  c.  Figure 21 shows case No. 3.  Figures showing the other  cases  would be quite similar.  Referring  to  figure 21, the following forces,  lever arms, and moments, all general  to cases Nos. 1 to 6, inclusive, are  noted:  (c)  F 6 •  D ue to increased pressure below the hull,  Fe  tends to rotate  entire airship in a positive direction about  M.  This is assisted by  reduced pressure beneath the tail (see fig. 17). The force below nose  and tail are opposite in direction.  T heir difference, since the nose  force is slightly the greater, is called dynamic lift of hull.  However,  both forces cause rotation in the same direction, and their moment  is referred  to  as dynamic upsetting moment,  Me.  I t will  be  evaluated  later.  NOTE.-Tbe force beneath the tail has been omitted from the figure in order  to avoid confusion in the drawing, the entire upsetting moment being treated  as though it were caused by the increased pressure under the nose.  (1)  Forces:  (a) L$_{9 }$ = Lifting force of gas.  (b)  W  = Total weight.  (c) Fe=Resultant air force on hull.  (d)  Le=  Vertical component of dynamic force on hull.  (e) Re=H orizontal component of dynamic force on hull.  (/ ) F a=Resultant force on tail surfaces.  (g)  L$_{8}$ = Li£t of tail surfaces.  (h.) R a=Drag of tail surfaces.  ( i)  T  =Thrust of propellers.  (j)  t  = Horizontal component of propeller thrust.  (k)  Lt=Vertical component of propeller thrust.  (2)  Lever mms about  G.-Lever arm of- (a)  W =k  sin  (a–8).  (b) L$_{9}$= o.  (c)  T  =  (c+h).  (d)  F$_{8}$ =a  (assuming  F,  perpendicular  to  the surfaces).  (e)  L$_{8}$ =a  cos  (a –8).  {f)  Rs=a  sin  (a–  8).  (g)  Fe  varies with the position of  P,  which in turn depends on  the angle  8.  (h)  L e=b  COS  (a–8).  (3)  Moments about  G.-Moment of- (a) Weight.  Defined as static righting moment.  It is present  irrespective of speed and at all times equals  W h  sin (a– 8).  (b) P ropeller thrust,  T  (  c +h). 