150 AEROPLANE PERFORMANCE CALCULATIONS 



the same type of cross section as in example (7), side by side, 

 with their centres 4^ inches apart, the struts of each pair being, 

 one I inch thick, and one 2 inches thick. 



Then as the shape is the same as in example (7), x is the 

 same. 



.-. * = -268. 



Also the total area is a = 2 x 5(2 + i) = 30 inch-feet units. 



Now the centres distance divided by the mean width is 



li., 



i 



Therefore the correction is I '194. Therefore the actual total 

 resistance of the four struts is given by 

 r = 30 x -268 x 1*194 = 9 '6 pounds at 100 miles per hour. 



Example (p). Resistance of Stream-line Wires. Fincl the 

 resistance of five stream-line wires of thread sizes \ inch, \ inch, 

 f inch, inch, and f inch respectively, and lengths 100, 95, 75, 

 70, and 68 inches respectively. 



Therefore the resistance of the batch is given by 

 r = 6*6 pounds at 100 miles per hour. 



Example (10). Resistance of Cable and Piano Wire. Con- 

 sider a batch consisting of a 10 cwt. cable 150 inches long, a 

 20 cwt. cable 100 inches long, and a 10 gauge piano wire 50 

 inches long. After looking up the diameters we find the resist- 

 ances are 



26 x -115(150+ 200 x -115)= 5*18 

 26 x -150(100+ 200 x -150)= 5-07 

 21 x -128(50 + 300 x -128) = 2-38 



Total r = 1 2 '6 pounds at 100 miles per hour. 



