’AIRSHIP AERODYNAMICS  TM 1-320  39=40  . shown by a member of the• National Advisory Committee for Aero› nautics that the algebraic sum of the forces on the fore and after  bodies is theoretically zero, which would indicate that the dynamic  lift on the hull was zero, and that the total lift obtained  dynamic~lly  by  the airship, exclusive of the vertical component of the propeller  thrust, was that furnis!1ed by the surfaces.  This is not in strict agree› ment with the actual facts, since the down thrust on the afterbody is  -less than the theoretical down thrust. However, the fact remains that,  since the pitch remains constant, the sum of the moments about the  , center of buoyancy must equal zero.  •  b.  The turning moment of the aerodynamic forces on the hull  theoretically equals the formula :  where O=angle of pitch.  k$_{2 }$ and k$_{1 }$=constants correcting for additional masses of air carried  longitudinally and transversely.  Values of k$_{1 }$ and  k$_{2 }$ are given in  National Advisory Committee for Aeronautics Report No. 184.  o.  If  it is granted that the dynamic force on the tail equals the total  resultant static transverse force, its moment must equal the formula  given  ~n  b  above. . Hence- where F = component of force on tail surface normal to longitu› dinal axis.  a=  distance from center of buoyancy to center of pressure  of tail surface.  ’The above formula will give an approximation of dynamic lift of the  airship.  .  d.  Practically,  F  need not be as large as indicated aboye due  to  the  discrepancy betwen actual and theoretical values of the down thrust  on the afterbody.  The point of application of  F  is slightly forward  of the center of the area of the tail surfaces.  e.  For method of calct1lation of shear bending moments due to  dynamic forces see paragraph 43.  40.  Transverse forces acting on airship in steady  turn.- The  theory  in  this case is quite similar to that described  in  paragraph 39.  • Assuming, as before, that the algebraic sum of the forces on the for&  .. :,  and after portions of the airship hull equals zero, the other two forces  :>acting on the airship (the force on the fins and centrifugal force) must. •  ...  .  ~  59  (Vol)iv 2 (k$_{2}$ -kl)  sin 20  Fa =  (Vol)~v 2 (kz-k 1 )  sin 20 