During the late 1930s, the Union Pacific often used helpers to move trains from Ogden to Wasatch. The UP wanted to simplify this move so they asked their "Department of Research and Mechanical Standards" to design a locomotive that could pull a 3600 ton train unassisted over the 1.14% grade of the Wasatch. The designers determined that to pull a 3600 ton train, a tractive effort of 135,000 lbs would be needed. Assuming a factor of adhesion of 4.0, the weight on drivers would have to be 4.0 * 135,000 = 540,000 lbs. Given an axle loading of 67,500 lbs each, this would require 8 drivers or an x-8-8-x wheel arrangement. The designers agreed upon the 4-8-8-4 design. Next, the horsepower and cylinder sizes were computed based on 300 psi boiler pressure. Although they weren't planning to pull these freight trains at 80 MPH, the DoRMS designed them for 80 MPH in order to have a sufficient factor of safety built into the design. What resulted is considered by many to be the most successful articulated steam locomotive ever built. 4000 was delivered to Omaha at 6PM, September 5, 1941.

$329.00
LIST: $467.00

SOLD OUT

$329.00
LIST: $467.00

SOLD OUT

$329.00
LIST: $467.00

SOLD OUT

$329.00
LIST: $467.00

SOLD OUT

HOME PAGE