TM 1-320  8  AIRSHIP AERODYNAMICS  (5)  Sphe-1-e.-The  air flow around a sphere (which more closely ap› proaches a streamline form) . is shown diagrammatically in figure 9.  It will be observed that the spreading out of the lines of flow before  reaching the sphere is less marked than for the flat plate in figure 5.  The coefficient of resistance of a sphere va.ries somewhat with the speed,  but for ordinary velocities its value is about 0.008.  The sphere is the  simplest geometrical form and is the most efficient shape for maximum  volume per unit weight but has a greater resistance than the more  perfect streamline form (see fig. 9).  ( 6)  Oylinder  (  longitudiMl  aaJis  horizontal).- The resistance of such  cylinders decreases wl.th length until the fineness ratio is approxi- mately 4  to  1, after which it increases. The increase is due to the effect  of slcin friction which will be discussed later. The relative resistance  of cylinders as compared to that of a flat plate of the same cross sec› tion is as shown  in  figure 10.  Where the fineness ratio is 4  to  1,  K = 0.00205.  19  li’IGOR!l 11.-Alr stream flowing by a cylinder (arts normal to air t’low).  FIGOREl 10.-Cyllnders.  R.= 1.00 fat- flat -pla.te  R.= .83 where L:o. = t  R= .77  where L: 0=3:1  ,.  , ...  X=  •?0123  fort=  .5 