182 



CHAPTER XXII. 



A TYPICAL MACHINE. 



General. This Chapter contains the complete performance cal- 

 culations of a particular machine, as it is hoped by that means 

 to elucidate points which may be obscure in the other parts of 

 the book. 



The machine we will deal with is illustrated by scale draw- 

 ings on pages 184 and 185. The wing section is No. 64 ; the 

 total weight is 6000 pounds made up as follows : structure in- 

 cluding fuel tanks, engine mounting and cowling, instruments 

 and all accessories, 2285 pounds; engine, 635 pounds; fuel 

 (petrol and oil), 2400 pounds ; cargo, 500 pounds ; crew (pilot 

 only), 1 80 pounds. The engine is a Dragonfly. As a designer 

 will appreciate at once, such a machine is well adapted to be a 

 long range carrier of special goods on paper but is open to 

 serious criticisms for practical reasons : that, however, need not 

 disturb us, as the machine is merely required to afford an example 

 of a complete set of calculations. Other data about the machine 

 will be given as they are required. 



Body Resistance. We will first decide on a propeller 

 diameter. The machine is loaded roughly 107 pounds per square 

 foot and 17*65 pounds per B.H.P. so that on general grounds we 

 may anticipate a top speed of the order of 100 miles per hour 

 if the propeller was designed for top speed. 



The machine, however, is intended for a cruiser, and we will 

 therefore suppose that the designer decides to have a 4-bladed 

 propeller designed for 80 miles per hour. Then V = 80 miles 

 per hour and we get from page 99, taking H = 340 and 



34O 

 d - io,ooo\ ill x I75tf x8Q = 106 inches. 



Hence we get the propeller circle shown dotted on the front- 

 view drawing of page 185. 



Parts in the Slip Stream. From a consideration of the pro- 

 peller circle on the front-view drawing we get with a little give 



