TM 1-320  17  AIRSHIP AERODYNAMICS  SECI’ION  III  POWER REQUIREMENTS  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):  Then the horsepower required to overcome this resistance is given by  the formula:  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- 31  Cn  p  (vol) 213 if• 86  H. P =  550  _ (0.0136 X 0.00237 X 3376.4 X 359000)  550  =71.1 horsepower.  Cn  p  (vol) 213 if• 86  H. P. =  550  R=  CD  p  (vol) $^{213}$ut.86  Paragraph  Power required to overcome airship resistance____________________________  17  Results of various speed trials------ - ------------------’----------------- 18  Burgess’ formula for horsepower- --•-- ------------- ------ ---------- - - ---- 19  Speed  devel~ped  by given horsepower____________________________________  20  Summary-------------------------- -------- - ______________ --•------------ 2l 