TM 1-320  42-48  AIRSHIP AERODYNAMICS  ing moment to be expected from such bumpy weather as would be en› countered in mountainous country:  Use of this formula enables the pilot to calculate rapidly maximum  stresses  to  which his velocity in bumpy air may be subjecting his  airship.  where Mb = the maximum bending moment in foot-pounds.  L =  the length of the airship in feet.  b.  Where surfaces are designed in approximate accordance with the  formula  A =  0.13 ( vol)  $^{2}$1 3 ,  the total transverse force on either vertical  or horizontal surfaces may be computed quickly by the relation:  In above formulas  A=total area of either surface.  F =  total force on either surface.  43. Method of calculating shear and bending moment on  hull.-a. The designer and also the pilot in determining shear and  bending moments on the airship must consider both static and dy› namic loads.  Both must  be computed independently and then added  together algebraically.  I t often happens that dynamic loads serve  to reduce stresses due to static loading, but naturally the dangerous  case occurs when stresses are arithmetically additive.  b.  The method to be described applies more particularly to rigid  airships, but the principle can be applied to a nonrigid.  In the latter  case, the load instead of being distributed throughout the length of  the hull is swung from the envelope by suspension cables which by  their tensions control very largely distribution of loading on the  envelope.  c.  For calculation of stresses, the hull is considered as a beam loaded  with the weights acting downward, lift of gas cells acting upward and  aerodynamic forces acting in any longitudinal plane whatsoever.  All  loads . are considered as concentrated at the frames rather than as  uniformly distributed.  The calculations may be divided into steps,  as follows:  ( 1) Calculation of static load.  (2) Calculation of shear due to static loading.  (3) Calculation of bending moment due to static loading.  ( 4) Calculation of load, shear, and bending moments due to aero› dynamic forces.  ( 5) Algebraic summation of effects of static and dynamic loading.  61  Mb=0.005 ,W  (vol) $^{213}$L  F = 0.026  (vol)  $^{2}$18  p v 2 • 