A wheeled tractor unit, operaing in its fourth$-$gear range ad at its full rated rpm$,$ is observed to maintain a steady speed

of $8mph$ when operating under the conditions described herein. Ambient air temperature is $60$ deg.F$.$ Altitude is sea level. The tractor is climbing a uniform $4\%$ grade with a rolling resistance of $55l\frac{b}{t}on,$ and it is towing a pneumatic$-$tired trailer loaded with fill material. The single$-$axle tractor has an operating weight of $74,946lb.$ The loaded trailer has a weight of $50,000lb.$ The weight distribution for the combined tractor$-$trailer unit is $52\%$ to the drive axle and $48\%$ to the rear axle.

$1$a$)$

The manufacturer, for the environmental conditions 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 $20$lbs of rimpull required per ton of weight per$\%$ of slope approximation is acceptable. Assume traction is not a limiting factor.

a Calculate GR here:

b Calculate RR here:

c Calculate TR here:

d Calculate required rimpull to move tractor here:

Weight of tractor here:

Weight load here:

e Horsepower required here:

$1$b$)$

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?

a$)$ Weight of the drive wheels here:

b$)$ Coefficient of traction here: