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the resistance is proportional to the two-thirds power of the volume. TMs leads to a more convenient expression for the resistance of airship hulls as follows : 

<img src='content_image/568538.jpg'>

where OD is called the P randtl shape coefficient after the eminent au› thority, Professor Prandtl. Values of 0 D for various speeds are given in table I. 

c. The offsets for different types of airships are given in table II. A study of the shapes given therein in connection with the Prandtl coefficients will bring out the relative efficiency of the different stream› lines. 

d. Certain general rules of design developed by experience and test may be summarized as follows: 

( 1) The best form is one of continuous curvature with radius of cur› vature constantly increasing toward rear portion. 

(2) T he shape of extreme rear portion of the hull does not seriously affect the resistance. 

( 3) The introduction of a cylindrical midsection causes an addi› tional resistance equal to the skin friction on the increased surface area of the hull. 

(4) The major diameter should lie between 33 and 40 percent of total length from the bow. 

11. Prismatic coefficient.- The ratio of the volume of any hull form to that of the circumscribing cylinder is called the prismatic coefficient, Qv. 

<img src='content_image/568539.jpg'>

The prismatic coefficients for different shapes are given in table I . . 

