Firebox heating surface included 111 sq ft (10.3 sq m) in seven inverted-T shape circulators and a combustion chamber extending 9 ft 3 in (2.8 m) forward of the ashpan. One of the heaviest engines in the world, the 25 "Big Boys" were the largest steam engines ever built for regular service. The last five delivered in 1944 were fitted with Type A superheaters; see Locobase 13026 for an analysis of why the change was made.
The Big Boys carried almost 70,000 lb (31,752 kg) more on its relatively tall drivers than did any other engine of comparable driver size. (The DM&IR's M3 2-8-8-4 engines -- Locobase 2405 -- had a higher weight on drivers, but had 63-inch/1,600 mm drivers.) Each one cost $265,000 when delivered.
These engines could maintain 70 mph (113 km/h) and rode quite steadily; see Locobase 338 for a description of the revised bearing design that permitted smooth riding at such speeds.. (The four pistons evacuated 22,700 cu ft/642.8 cu m of steam per minute at that speed.) On the other hand, Farrington (1976) claims they were hard to fire and thought a feedwater heater should have been preferred to the exhaust steam injector they carried.
Over a ruling grade of 1.14% the 4-8-8-4s could move 4,000 tons (3,636 tonnes) of freight at 20-25 mph (32-40.25 km/h). When the ruling grade between Ogden, Utah and Green River, Wyoming (176 miles/283 km) was reduced to 0.82%, the tonnage rating climbed to 5,360 tons (4,873 tonnes). At 45 mph (72.5 km/h), these engines developed 6,000 drawbar horsepower (4,476 kW). Among their many abilities was the flexibility to move around curves of 20 deg.
Also, the online encyclopedia http://www.answers.com/topic/union-pacific-big-boy (visited 14 July 2005) notes approvingly: "They did sterling service in the Second World War, especially since they proved so easy to fire that even a novice could do a fair job. Since many men who were unsuited to combat service were instead drafted into railroad service to replace crewmen who joined up, this proved essential."
See the trainorders.com forum thread that began 1/05/13 (http://www.trainorders.com/discussion/read.php?10,2959319) when KeyRouteKen commented on a recent documentary: "One of the guys talked about shoveling 27 tons of coal "by hand". Stoker must have been inoperable. Then he said they dropped down one time to 165 lbs of steam so they threw some creosoted pieces of crossties in the firebox to raise steam again. That was funny.
"And the best story was the guy who would open the firebox door and hold his shovel there to make a vent. Great, except when the hogger pulled back on the throttle, and the entire shovel was sucked into the firebox ! (grin!) "
Bob3985 replied:"The fireman who hand fired the Big Boy was Dillard Hill and they indeed had broken the stoker auger and could not auto deliver the coal to the firebox so they set their train out and made a run for the Laramie roundhouse keeping the steam up by hand."
Hotwater added:"... hand firing any locomotive equipped with a stoker, it really isn't THAT big of a deal. Just because the stoker auger doesn't work, does NOT mean that the steam distributing table doesn't function. All that is needed is for one or two men (Fireman & Headend Brakeman) to continuously shovel the coal onto the distributing table, and the steam jets will blow the coal to the necessary portions of the firebox. I speak from experience! It works on any steam locomotive equipped with a stoker."
Drawing from William Kratville's book Big Boy, Nick Chillianis posted information about tests conducted 3 April 1943 on the Wasatch grade. Pushed at a rate of 9,980 US gallons (37,434 litres) of water and 9.66 tons (8.8 tonnes) of coal consumed per hour, engine #4016 produced 7,157 hp (5,339 kW) at the cylinders while moving 3,883 tons (3,530 tonnes) of train at 41.1 mph/66 km/h (drawbar hp was 6,290.) Other engines in the test produced 5,800 dbhp (4,327 kW) under similar conditions. See http://www.chaski.com/wwwboard/railfan/messages/3993.htm (12 Nov 1998, 8:46 AM).
Locobase 346 describes the first 20 of these Big Boys. This later quintet is usually described as reflecting the wartime limitations of certain metals, which required the builder to substitute heavier steel components. Even so, their engine weights were still lower than the maximum weights believed to have afflicted the C & O's 2-6-6-6 H-6 Allegheny class (Locobase 304). Firebox heating surface included 111 sq ft (10.3 sq m) in seven inverted-T shape circulators and a combustion chamber extending 9 ft 3 in (2.8 m) forward of the ashpan.
What is not usually mentioned is the change in boiler heating surface area and the substitution of a Type A superheater for the earlier group's Type E. John E. Rimmasch of
Wasatch Railroad Contractors contributed to a Trainorders forum discussion with comments that shed light on the reason for the change (http://www.trainorders.com/discussion/read.php?10,2474974):
On May 25, 2011, Rimmasch lays out the conditions that most likely dictated the change: "On the UP between 1941 and the end of steam, it was not uncommon to see super power get new tubes annually or even every six months. This was due in large to a number of conditions. A.) The water in Utah and Wyoming was hard enough that the flue bundle would clog up and tubes would burn quickly. B.) The UP Super Power was high pressure steam, which means we had a lot more heat. 800's, 300 psi, Big Boy's 300 psi and Challengers 280 psi. C.) The length of the tubes in the 800s, 3900s and 4000 was nearly the maximum allowable tube length for any locomotive (respectively 20-22 feet [6.1-6.7 m] long). It was found that when tube lengths near or surpass 18 feet long [5.5 m] , they had more of a tendency to bounce and tear apart. The stretching effect on these long tubes precluded many of them from being re-used.
"In the case of the UP, when you combine all three symptoms above, you end up having to change tubes more often ... [R]ather than lose a locomotive on tube failure, the UP (and other lines) found it cheaper and better to simply change them more frequently. ...A Big Boy could get new tubes in less than 36 hours."
In a later post, Rimmasch argues that Alco used a Type E superheater, which was harder to maintain because of its more complex steam path, to cover its bets: "I assume that the Big Boy originally had type E's with an increased heating surface area as ALCO was unsure if they had produced enough heating surface area to support the bore and stroke (multiplied by 4) and, after delivery quickly found that they had enough steaming capacity that the locomotive did not require type E's and was therefore reduced to type A's."
Rimmasch implies that the change to Type A superheaters came during the production of the first 20 locomotives, but the 1946 diagrams show only that the 4884-1s had Type E and the 4884-2s had Type As.
|Specifications by Steve Llanso|
|Class||Big Boy (4884-1)||Big Boy (4884-2)|
|Railroad||Union Pacific (UP)||Union Pacific (UP)|
|Locomotive Length and Weight|
|Ratio of driving wheelbase to overall engine wheebase||0.26||0.26|
|Overall Wheelbase (engine & tender)||117.58'||117.58'|
|Axle Loading (Maximum Weight per Axle)||67800 lbs||67800 lbs|
|Weight on Drivers||540000 lbs||545200 lbs|
|Engine Weight||762000 lbs||772250 lbs|
|Tender Light Weight||427500 lbs||436500 lbs|
|Total Engine and Tender Weight||1189500 lbs||1208750 lbs|
|Tender Water Capacity||24000 gals||25000 gals|
|Tender Fuel Capacity (oil/coal)||28 tons||28 tons|
|Minimum weight of rail (calculated) on which locomotive could run||113 lb/yard||114 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||300 psi||300 psi|
|Cylinders (dia x stroke)||23.75" x 32" (4)||23.75" x 32" (4)|
|Tractive Effort||135375 lbs||135375 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||3.99||4.03|
|Firebox Area||704 sq. ft||720 sq. ft|
|Grate Area||150.30 sq. ft||150 sq. ft|
|Evaporative Heating Surface||5889 sq. ft||5755 sq. ft|
|Superheating Surface||2466 sq. ft||2043 sq. ft|
|Combined Heating Surface||8355 sq. ft||7798 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||179.46||175.37|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||45090||45000|
|Same as above plus superheater percentage||58617||56700|
|Same as above but substitute firebox area for grate area||274560||272160|
|4004 smokes up the sky near Speer, WY, heading a manifest of empty fruit reefers back to western producers. Photo by Stan Kistler, Winter 1958.|
|4015 pokes out from under the coaling tower at Denver, CO as Challenger 3954 stands by on a cold day in Winter 1954. Photo by R. H. Kindig.|
|4016 storms upgrade near Perkins on the southern "Harriman" line with a westbound consisting of empty hoppers. Photo by Donald Duke, Fall 1958.|
|4017 and a westbound mixed manifest round a curve on the approach to Green River, WY. Photo by R. H. Kindig, 1957.|
|4017 drags a seemingly endless string of reefers westbound through the tree-studded countryside west of Harriman, WY. Photo by R. H. Kindig, 1957.|
|This is probably one of the most famous of all Big Boy photographs. It was taken during the usual 10 minute stop near Echo to cool the train's wheels after the long braking descent from the top of the Wasatch grade. photo credits|
|4019 and engineer take a brief rest from their work at Cheyenne, WY during the Big Boys' final summer. Photo by R. H. Kindig, 1958.|