84 



HANDBOOK OF MECHANICAL DESIGN 



(X = 



45,000 X 1.368 61,500 



41,000 



1.368 + 0.3682 1 504 

 K„ = 13 (assumed) 



?- = SsT = 41,000 tanh 13.6 X 0.040 



Ji- 



= 20,200 lb. per sq. in. stiff ener allowable 



Fig. 13. — Curves for calculating the load carried by a curved skin reinforced Ijy fore and aft stringers. 



This is the allowable P/A of the stiffeners. The allowable load P that the curved 

 sheet reinforced by the stringers can carry is equal to 



p = cf- V^ 



ST 



where E = modulus of elasticfty = 10,500,000 

 t = sheet thickness 



C = coefficient dependent upon the para- 

 meters n and X 



The value of C is obtained from the curves in 

 Fig. 13 after n and X have been calculated from 

 the formulas (see Fig. 12 for the numerical values 

 used for b, R and t) 



b 



42.5 



8.35 10,500,000 



n = -TTn: -x -^^tt^^t;^ — = 4.48 



20,200 



= i /A 



b \ SsT 



t = sheet thickness = 0.032 in. 



R 



Ve/Ss 



where h = stiffener spacing = 8.35 in. 



R = radius of curvature = 42.5 in. 

 SsT = 20,200 lb. per sq. in., from the pre- 

 ceding calculated stiffener allowable 



_ 0.032 10,500,000 

 ^ " 8.35 V 20,200 



= 0.088 



From the curves, Fig. 13 for n = 4.48 and 

 X = 0.088, 



C = 2.8 

 Hence, solving the equation for total load allowable on sheet, 



p = cr- ylM^T 



= 2.8 X 0.032- Vl0,500,000 X 20,200 

 = 2.8 X 0032^ X 3,245 X 142.2 

 = 1,325 1b. 



