Power Grab: The Tractor Horsepower Race

From humble beginnings, manufacturers deliver increasingly powerful farm tractors.

| November 2019

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Case built 110hp steam engines like this between 1913 and 1925. Photo courtesy Robert Pripps.

In 1781, as the story goes, Scotsman James Watt struggled to convince skeptics to buy his new steam engine as a replacement for their draft horses. To prove his machine’s superiority, he measured the pulling force of a horse walking in circles to turn a mill grindstone. Multiplying its pulling force (approximately 180 pounds) by the distance covered in one minute (a little over 180 feet), Watt came up with a new unit of measure: horsepower.

Perhaps the horse could have pulled harder, or could have been urged to go faster – or Watt could have gotten a bigger horse. Nevertheless, what Watt came up with – 550 foot-pound-seconds – was established as horsepower, a rate of doing work.

Watt’s steam engine, by the way, proved to be the equivalent of 33 horses. With that, he began the trend that would eventually, almost completely, replace the horse with mechanical horsepower. On the farm, where the problem is that all the work needs to be done at once, more horsepower has helped to provide the solution.



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Plowing with steam: An Advance-Rumely Universal steam engine pulling a 6-bottom plow. At the turn of the last century, steam engines proved their mettle as farmers tackled the virgin prairie. Photo courtesy Sam Moore. 

 
In the latter half of the 19th century, steam provided the needed horsepower. Watt’s 18th century engine, however, was a far cry from the steam engines we now see at antique farm power shows. Metallurgy limitations in the 16th and 17th centuries precluded the manufacture of accurate cylinders, and the cylinders of that era could not withstand much pressure. In fact, Watt’s early engines used evaporating steam to evacuate the cylinder so as to allow atmospheric pressure to force the piston to travel its stroke.

The romance of steam

The mystique of the steam engineer seems to be universal. People of all ages look up to steam engineers as they pass by, high up in the chuffing behemoth’s cab, be it on rails, the farm or at a thresheree. This was also the case at the dawn of the 20th century, especially on the farm. The main jobs of the steam engine then were plowing and driving a thresher. Steam also powered the sawmills that made the lumber that built America’s cities.



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