11 



Appendix I 



The physical assumptions we have made above concerning the components of the 

 forces on the cable normal and parallel to it are based on the experiments and data 

 of Relf and Powell (R.and M. No. 307, January, 1917). They measured the lift and 

 drag of an infinite, straight cable, situated in a uniform stream of air, and in- 

 clined at an angle <|> to the direction of air flow. 



Let R be the force per unit length acting on the cable when it is normal to 

 the wind. Let F be the force per unit length acting on the cable when it is paral- 

 lel to the wind. Our assumptions then are that for a given speed the components of 

 the force per unit length acting on the cable are R sin a $ normal to the cable and 

 a constant F parallel to the cable. The values of the normal and parallel compo- 

 nents were computed from the paper cited above for the case of a stranded wire 

 cable of diameter 0.388 inches. Relf and Powell made their measurements with a wind 

 speed of 40 ft. /sec. The experimental results are compared with the assumed laws 

 in table 5 and fig. 4 taking R = .074 and F = .0023. 



TABLE 5. 



Normal Component 



Tangential Component 



i> 



Experimental 



.074 sin a * 



Experimental 



F. 















.0023 



.0023 



10° 



.0027 



.0022 



.0028 



.0023 



20° 



.0089 



.0087 



.0031 



.0023 



30° 



.0174 



.0185 



.0033 



.0023 



40° 



.0280 



.0306 



.0033 



.0023 



50° 



.0409 



.0434 



.0033 



.0023 



60° 



.0544 



.0555 



.0023 



.0023 



70° 



.0654 



.0654 



.0018 



.0023 



80° 



.0735 



.0719 



.0010 



.0023 



90° 



.0740 



.0740 







.0023 





C 



JRV 



ES 



Sh 



ow 



NG 



u 



w 



OF 



TO 



ICi 



Oi 



t A 



Wl 



*E 













<ii 













-J81 



"s 



TIM 



DEI 



o 



Jt-E 









/ 









































/ 









































/ 









































/ 



















~ UJ 























/ 





















* 





















fy 























g« 



















t 



7 























J 



















/ 

























I" 

















/ 









































/ 









bHW 



MM 









WT1A 







H 



['L 















/ 









































/ 



,... 















































































































r 











































