T = 2yP„W (B-4) 



where y = coefficient of friction between fabric and metal 

 P = clamping pressure provided by the bolts (psi) 

 W = width of clamping channel (in.) 

 T = tensile load over boom height (lb/in.) 



From Reference 4, the tensile load, F, in pounds that can be 

 imposed on a bolt by hand tightening of a nut can be approximated by 



F = 16,000 X (bolt diameter, inch) 



Therefore, for 3/8-inch-diameter bolts the approximate load is 6,000 

 pounds. Using a bolt spacing of 3.5 inches to maintain a nearly uniform 

 clamping pressure results in an ''influence area'' of 9.65 inches square 

 and a clamping pressure, P , of about 625 psi for each bolt. 



Tjrpical values of v range from 0.04 (Teflon on steel) to 0.61 

 (leather on oak). Assuming a value for y of 0.10 and the value of P 

 given above. Equation B-4 becomes, after solving the width, W, 



W = ^ (B.5) 



As shown in the hydrodynamic drag calculations of Appendix A, 

 the maximum tensile load occurs for the Type II boom in a catenary 

 tow. With the assumption that 50% of this load will be carried by the 

 fabric and 50% by the primary tension members, the resulting vertical 

 loading, T, is 190 lb /in. of fabric. Inserting this value of T in 

 Equation B-5 gives a maximum required clamping channel width of 



W = 1.5 inches 



Therefore, to assure that the fabric boom is not pulled out of the 

 connector, a clamping plate at least 1.5 inches wide using 3/8-inch 

 bolts on 3.5-inch centers is required. 



TOWING ASSEMBLY 



A serviceable towing assembly must be rigid enough to resist the 

 bending and buckling loads that will occur in field service, must still 

 be able to maintain the boom in a vertical attitude, and must provide 

 a proper towing load distribution over the vertical boom end. 



41 



