## (solution) A wheel-type tractor unit, operating in its fourth-gear range and at its full rated rpm, is...

A wheel-type tractor unit, operating in its fourth-gear range and at its full rated rpm, is observed to maintain a steady speed of 730 mph. when operating under the conditions described herein. Ambient air temperature is 60°F. Altitude is sea level. The tractor is climbing a uniform 5.5% slope with a rolling resistance of 55 lb/ton, and it is towing a pneumatic-tired trailer loaded with fill material. The single-axle tractor has an operating weight of 66,000 lb. The loaded trailer has a weight of 48,000 lb. The weight distribution for the combined tractor-trailer unit is 55% to the drive axle and 45% to the rear axle. a. The manufacturer, for the environmental conditions just described, rates the tractive effort of the new tractor at 330 rimpull horsepower. What percentage of this rated rimpull hp does the tractor actually develop? The "20 lb of rimpull required per ton of weight per % slope" approximation will be acceptable. Assume traction is not a limiting factor. b. What is the value of the coefficient of traction if the drive wheels c the tractor are at the point of incipient slippage for the conditions p described?

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Sep 13, 2020

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