close to the towed ends. The plate thickness, b, of the first candidate 

 connector (shown in Figure B-IA) necessary to accept this load without 

 failure is given by 



where a = tensile stress (psi) 

 F = tensile tow load (lb) 

 i = boom height (in,) 



Using a maximum allowable stress of 35,000 psi, a tow load of 

 13,600 pounds, and a boom height of 36 inches, Equation B-1 yields a 

 required thickness of 



b = 0.037 inch 



This calculation indicates that a very thin plate could be used 

 if it were subjected to a pure static tensile load of 13,600 pounds. 

 However, stress concentrations created by the presence of holes and 

 attachment of primary tension members occur in practice which would 

 require an increase in thickness over this value. From Reference 3 the 

 stress-concentration factor for a hole one diameter away from the edge 

 of a plate is about 3.6. A plate thickness of 0.25 inch, instead of 

 0.037 inch, is used in the remaining calculations, resulting in a safety 

 factor of about 6.8 which should allow for the stress-concentration 

 factors mentioned above. 



The maximum stress on the large connector tube (see Figure B-IA) 

 due to a tensile tow load occurs on the outside edge. The size of the 

 tube wall is determined using the free-body diagram of Figure B-IB. 

 From equilibrium considerations of this diagram, the wall thickness, 

 t, is determined from the equation 



a = Z-J3.5 + 3f) (B-2) 



where the symbols are as defined for Equation B-1 or indicated in Figure 

 B-IA, 



Using the same values as used in Equation B-1 the wall thickness 

 is given by Equation B-2 to be 



t = 0.36 inch 



39 



