Bulletin: *Big Boy 4-8-8-4*

*Big Boy 4-8-8-4*

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" (DoRMS) 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.

The 25 Big Boys were built in two groups. The first group, called "class 1", were built starting in 1941. They were numbered 4000-4019. The second group, "class 2", were built in 1944. They were numbered 4020-4024. The last revenue freight pulled by a Big Boy was in July of 1959. Most were retired in 1961. The last one was retired in July of 1962. As late as September, 1962, there were still four operational Big Boys at Green River, WY.

Key Function Soundslots Volume CVs Volume value
LightDirectional Headlights / Dynamo6299128
F2Playable Whistle3275128
F3Coupler Clank5291128
F5Aux3 (Firebox)
F7Switching Mode
F8Prime Mover Sound On / Off (Mute) 1, 2, 17, 24259, 267, 387, 443128, 128, 80, 99
F9Dimmer (Headlights)
F10Air Pump7307128
F11Oil Burner14363128
F12Coal Shoveling15371128
F15Crossing Communication10331128
F16Rail Clank (works only if F8 is On) 1133960
F17Brake Set / Release12347128
F18Sanding Valve13355128
F19Open Cylinder Cocks18395128
F20Short Whistle16379128