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## SECI’ION III POWER REQUIREMENTS 

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17. Power required to overcome airship resistance.-a. To maintain uniform velocity in flight, resistance of the airship must be overcome by thrust of the propellers. The work done by the pro› pellers equals the product of the resistance times the distance through which the airship moves. • 

b. The unit of work in the English system is the foot-pound, or the quantity of work performed by 1-pound force acting through a dis› tance of 1 foot. Hence work done in propelling the airship in foot› pounds equals resistance in pounds times air distance traveled by the airship. 

a. Power is defined as the rate of doing work, 1 horsepower equaling 550 foot-pounds per second. Therefore the power utilized to over› come hull resistance must equal resistance multiplied by velocity in feet per second divided by 550. 

d. The resistance is given by the equation (see sec. II): 

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Then the horsepower required to overcome this resistance is given by the formula: 

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e. Problem and solution-(1) Problem.-What horsepower will be required to drive an airship of 195,000-cubic-foot capacity at 60 miles per hour ( 88 feet per second) in atmosphere of standard density~ The envelope shape coefficient is 0,0136. The propeller efficiency, E, is 60 percent. The envelope resistance, F, is 40 percent of the total resistance of the airship. 

(2) Solution.-The horsepower necessary to overcome hull re› sistance is given by- 

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