Question

# A fully loaded CAT 621G scraper is operating in fifth gear at its full rated rpm. Ambient air temperature is 60°F and the altitude is approximately sea level. The scraper

is climbing a uniform 4.0 %slope with a rolling resistance of 7O Ib/ton and the pneumatic-tired scraper bowl is fully loaded with fill material. a. What is the operating weight ofthe empty scraper (Ib)? b. What is the rated load in pounds for this scraper? b. What is the rated load in pounds for this scraper? c. What is the total operating weight of the fully loaded scraper? d. What portion, in pounds and percent, of the fully loaded weight is carried by the front axle? e. What portion, in pounds and percent, of the fully loaded weight is carried by the rear axle (the axle of the bowl)? f. What is the speed of the scraper in mph when operated in fifth gear(forward)? g. At what net horsepower does the manufacturer rate the tractive effort of the scraper, for the environmental conditions described and operating in fifth gear? h. What percentage of this rated rimpull does the tractor actually develop? In performing your calculations, it will be acceptable to assume that the component of weight normal to the traveling surface is equal to the weight itself(i.e., cos 0 taken as 1.00, where 0°is the angle of total resistance). The"20 Ib of rimpull required ton of weight per % of slope"approximation will be acceptable.You may also disregard the power required to overcome wind resistance and to provide acceleration. Assume traction is not a limiting factor. i. What is the value of the coefficient of traction if the drive wheels of the tractor are at the point of incipient slippage for the conditions just described?

Fig: 1

Fig: 2

Fig: 3

Fig: 4

Fig: 5

Fig: 6

Fig: 7

Fig: 8

Fig: 9

Fig: 10

Fig: 11