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. 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. 

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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- 

<img src='content_image/580504.jpg'>

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. • ... . ~ 

