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CHAPTER XV. 



BODY RESISTANCE. 



Example (l). Resistance of a Fuselage. Take the case of a 

 fuselage whose maximum cross section is a rectangle, 26 inches 

 wide by 36 inches deep, with an arched top rising 5 inches at 

 the centre. 



First find the area of cross section by using a planimeter on 

 the drawing of the cross section. This gives a = 7 -07 square 

 feet. 



.-. r = 2*5 x 7-07 = 177 pounds at 100 miles per hour. 



The resistance of windscreen, cockpit, etc., is not included in 

 the above. 



Example (2). Resistance of a Nacelle. Take a nacelle of 

 the same cross section as above. Then (again, of course, ex- 

 cluding windscreen, etc.) 



r = 7 x 7-07 = 49*5 pounds at 100 miles per hour. 



Example (3). Resistance of an Engine Egg. Take a circular 

 egg of 43 inches diameter (such as would be used for a large 

 stationary radial engine). Then, excluding the resistance of 

 projecting cylinder heads or engine cooling louvres, since the area 

 is 10*09 square feet, 



r = 7 x 10-09 = 7'6 pounds at 100 miles per hour. 



Example (4). Resistance of a Flying Boat Hull, Including 

 the Steps. Consider the case of a flying boat hull whose maxi- 

 mum cross section is an egg-shaped oval 3 feet 6 inches beam 

 by 3 feet 1 1 inches deep ; further we will suppose that the egg 

 shape is not a very great departure from elliptical form, then we 

 can save ourselves the trouble of using the planimeter by taking 

 the elliptic formula 



a = 3'5 x 3'9i8 x - = 1075 square feet. 



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Therefore the resistance of the hull without cockpits or 

 steps is 



i '3 x 1075 = I 4' pounds at 100 miles per hour. 

 Now suppose that there are two steps, of which the front one 

 has a maximum depth of 2 inches, and a beam of 4 feet, and the 



