TM  1-320  8  AIR CORPS  (7)  OyUnderr  (vertical).-When  a cylinder of given cross-sectional  area is placed with its axis of revolution at right angles to the direction  of motion the resistance depends upon the fineness ratio of the cylinder.  When the length and diameter of the cylinder are the same the coeffi› cient of resistance is only slightly greater than for a sphere of the same  cross-sectional area.  When the length-diameter ratio is increased to  4 to 1 the coefficient of resistance is approximately doubled, or  K  =0.0018, and if the length-diameter ratio is reduced to one-half (or  0.5/ 1) the coefficient of resistance is increased 27 percent, or  K  =0.00123  (see fig. 11).  .  (8)  Cylinder with hemispherical ends.-It  is possible to reduce  greatly the resistance of a cylinder  by capping the ends with hemi- spheres. The resistance is reduced to 20 percent of that of a cylinder  with flat ends. The value of  K  for a cylinder with hemispherical ends  •and a fineness ratio of 4 is approximately 0.0006 (see fig 12).  (9)  Wires and cables.- Wires and cables may be considered as cylin› ders of very long length. E xperiments show that the resistance of wire  or stranded cable when placed normal to direction of motion is very  nearly equal to the resistance  of  a flat plate of the same projected area.  The gain by the circular form of the wire is counterbalanced by its very  20  FIGURE 13.  WIRJ:S  CABLES  X:  . 0026  K: . 0013  -~  K  =.  0015  X =  •  0029  ·~  •  - FIGURE 12.-Air stream flowing by a cylinder (hemispherical ends) .  L  K  = .  0006  for  D  =  4 