TM 1-320  8  AffiSHIP AERODYNAMICS  great length.  The resistance of a long, narrow object perpendicular to  direction of motion is greater than that of a more symmetrical form.  The experimentally determined value of the coefficient of resistance is  0.0029 for stranded cables and 0.0026 for smooth wires.  K  is almost in› dependent of the diameter for all sizes of  wire and cable.  Stranded wire or cable  ha~  a resistance about 14 percent greater than  solid wire.  (a) The above discussion relates only to  wires and cables perpendicular to the wind  direction or direction of motion. . When a  wire or cable is inclined to the perpendicular  its resistance is very much decreased as the  air flows around it in more uniform stream› lines or in a more gradual curved path. An  inclination of about 30° from the vertical  reduces the resistance 20 percent and an in› clination of• 45° reduces the resistance 50  percent.  (b) When two wires or cables are close  together and placed one just behind. the other  there is a reduction in resistance due to  shielding of the second wire by the first.  If  they are placed very close together their  combined resistance is considerably less than  the resistance of one wire .alone, as the two  wires have the effect of an increased fineness  ratio.  If  they are spaced more than 3ljz di› ameters their combined resistance becomes  greater than a single wire but is still less  than the resistance of the two wires tested  separately. This shows that if two wires or  cables are close together (within 5 diameters  of each other) it is very advisable  to put a filler block in between  them, thus preventing the air from flowing in between them and .  giving them the advantage of a single member of high fineness-ratio.  If  the two wires are streamlined  in  this way their combined resistance  can be kept down to about 50 percent of the resistance of a single  wire until their fineness ratio becomes greater than seven.  The high  value of the resistance caused by wires and cables immediately sug› gests reduction of wires and cables to the minimum by means of  refinements in design and arrangement.  - .  21  FIGURE 14.-Struts.  N.PL. "I  N.P! ..  $^{1}$2  .  Fimnessl!t:dto 4j/!. K=.ooo4  N.PL  11’..3  ’  /’inmes.s  ~crlto  41% K:.OOQ38  NP.J.. ..-4  ~-r-:- •- •- · ~  ’  "/  /  - ~  /  l'lnen~ss  Raho  2/1  1<Q.ooo8:J 