America
by Jon Burch Photography
Title
America
Artist
Jon Burch Photography
Medium
Photograph - Digital Capture & Enhancement
Description
In 1936, Union Pacific introduced the Challenger-type (4-6-6-4) locomotives on its main line over the Wasatch Range between Green River and Ogden. For most of the route, the maximum grade is 0.82% in either direction, but the climb eastward from Ogden, into the Wasatch Range, reached 1.14%. Hauling a 3,600-short-ton freight train demanded double heading and helper operations, which slowed service. So Union Pacific decided to design a new locomotive that could handle the run by itself: faster and more powerful than the compound 2-8-8-0s that UP tried after World War I, able to pull long trains at a sustained speed of 60 miles per hour once past mountain grades.
Led by Otto Jabelmann, the head of the Research and Mechanical Standards section of the Union Pacific Railroad Mechanical Department, the design team worked with the American Locomotive Company to re-examine their Challenger locomotives. The team found that Union Pacific's goals could be achieved by enlarging its firebox to about 235 by 96 inches or about 150 square feet, increasing boiler pressure to 300 psi, adding four driving wheels, and reducing the size of the driving wheels from 69 to 68 inches on a new engine. The new locomotive was carefully designed not to exceed an axle loading of 67,800 pounds, and achieved the maximum possible starting tractive effort with a factor of adhesion of 4.0. It was designed to travel smoothly and safely at 80 miles per hour, even though it was not intended to be used that fast.
To achieve these new engineering goals, the locomotive was "comprehensively redesigned from first principles," according to locomotive historian Tom Morrison. The overall design simplified some aspects of previous locomotive designs and added complexity elsewhere. Compounding, booster, and feed water heaters were eliminated, as were Baker valves and limited cut-off. But the "proliferation of valves and gauges on the back head showed that running a Big Boy was an altogether more complicated and demanding task for the crew than running previous existing locomotives.”
The 4-8-8-4 class series, originally rumored to be called the "Wasatch", acquired its nickname after an unknown worker scrawled "Big Boy" in chalk on the front of Number 4000, then under construction as the first of its class.
Photograph made during a Thanksgiving snowstorm north of Greeley, Colorado at US 85 and "AA Street" while standing in a snow drift at the side of the road...
Image copyright 2019 Jon Burch Photography
Uploaded
December 1st, 2019
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