Challengers leaking or Big Boys leaking? I read the Big Boy did not perform well when converted to oil, and was quickly converted back to coal, with no further attempts to convert a big boy to oil.
What was the leaking problem? (I only have read 3 of Kratville’s books: the two 4-12-2 books and The Challengers, which makes reference to earlier works on the Big Boy and the 4-8-4, but doesn’t repeat any of that material, instead assuming the reader will have read them).
If I recall correctly, Huddleston said something about the size and shape of the Big Boy firebox not being as conducive to oil burning as the Challenger. No author is perfect…was that just opinion and not true?
N&W first made the claim in 1936; in 1941 Railway Age, Pond said the A’s maximum “sustained horsepower at the drawbar” was 6300 at 45 mph. As always, we haven’t the faintest idea what “sustained” means.
Obviously they could make 25 mph with some sort of reduced tonnage, but no reason to think the UP was hoping for 25 mph on 1.14% with 3600 tons or 4450 tons or anything like that. What did Huddleston actually say?
He wrote in World’s Greatest Steam Locomotives, in one of the sections where he discusses the Big Boy and the dynamometer tests on it, that UP’s own publicity stated they wanted to take an entire train (tonnage not specifically given) over the Wasatch with a Big Boy unassisted, and he added that they wanted to do that at 25 mph. Apparently during the various tests, they found the best a Big Boy could actually do was about 17 or 18 mph, and that to haul the typical train length they wanted (70 cars or more) at the speed they wanted, that they ended up needing two Big Boys, which was viewed as unacceptable.
I’m assuming 70 cars is about 3600 tons?
He states they eventually found that two Challengers, one front and one on the rear, was the ideal motive power solution for 70 car trains eastbound over the Wasatch. Kratville corroborates the use of two Challengers (at least one an earlier 3800 class) as being the preferred power in The Challengers, but didn’t specifically discuss the preferred train length/weight anywhere in that book that I am able to find. Kratville did comment that Union Pacific men were very sorry to see the Challengers go from the Wasatch because they did a terrific job.
Perhaps from the time the Big Boy was introduced until the time of the tests later in the 1940’s, UP’s idea of a “typical” train length over the Wasatch actually increased quite significantly?
Perhaps I misunderstood/misquoted Dr. Huddleston’s work.
As I said above, the book is currently loaned out to a friend. I’m unable to look up the page right now.
page 39:
From a steaming standpoint, the 4005 steamed better
than any oil burning power UP men had
seen on the road. However, the single burner
caused spot heating on the huge crown sheet
which in turn, caused it to leak. Every trip
was the same - when you lookes in the firebox
it was just like a rainstorm, with water poring
down so fastthat it almost exstinguished the
fire!
A standard Thomas oil-burner was installed…
Of course they leaked, but I believe that problem could have be technically resolved.
The most likely reason was, the single oil burner did not fit with the distances of oil refueling service points along the line. These points were more accommodated and suitable for passenger trains than for freight trains with a 4000 class. Therefore, further investigations were not followed…
I wanted to see under what conditions an as-built Class A (275 psi, no circulators) could develop 6,300 DBHP. Here’s what I did:
Unit evaporation, 92 lbs/SF direct heating surface, not at all out of reach. Johnson considered 125 lbs/SF DHS high
116,055 lbs/hr total evaporation (actual figure)
8% to auxiliaries
107,000 lbs steam/hr to engines at 300 deg superheat
6,900 lbs total locomotive resistance at 45 mph
6,300 dbhp at 45 mph (purportedly an actual figure)
So 6,300 may have been possible, as Pilcher said, under unusual conditions, but none of the above numbers are outrageous. N&W normally didn’t push its locomotives above a unit evaporation of about 80 lbs/SF DHS/hr even on tests. N&W’s rated DBHP readings were generally daily achievable in-service figures, very conservative compared to some other roads. Maybe that’s why Pilcher used the word “unusual”.
Rapidly flowing water is better for heat transfer than relatively stagnant water, so any loss in effectiveness with respect to the sheets would have more to do with the amount of heat transferred from the combustion products to the syphon. Heat transfer to the “Direct Heating Surface” is largely radiative, so the parts of the syphon facing the sheets would be in sort of a shadow and possibly getting less heat than the parts pacing the interior of the firebox.
Maybe N&W thought syphons weren’t worth the extra installation and maintenance costs compared to circulators. There’s a lot of welding on the top part of a syphon, and they’re in the middle of a high stress environment, thermally and physically.
The A’s DHS excluding circulators is 530 SF; the EM-1 is 545 SF excluding syphons, 3% more than the A. This seems to indicate that the firebox volumes may not be that much different. Arch tubes make up 10% of the total Class A DHS; the EM-1’s syphons make up 28%.
So, I still have to wonder - does a square foot of syphon/circulator transmit the same amount of heat as a square foot of crown and side sheets? It seems that it would take a certain amount of time for the hot metal to transfer heat to the water passing through. Sort of like dipping your finger in hot water. If you’re quick enough, you won’t get burned. With a dwell time of 3-4 seconds, there may be a different result!
That’s a good question that for a steam locomotive might be hard to answer in this day and age. I would think that a well designed and integrated thermic syphon(s) were be quite efficient in absorbing radiative heat. Whether or not they are equal to the crown sheet, I have no idea. They would be far better that any indirect convective surface area.
The builders had no choice at that point other than to add syphons / circulators to the design. These large locomotives were at the limit of useful size. The EM1 was only 6 feet shorter than a Big Boy, and most of that was due to a smaller, shorter 6 axle tender. There simply wasn’t any more room to physically enlarge the firebox/combustion chamber. To give the EM1 a total of 760 sq.ft. direct heating surface, the additional surface had to come from internal sources (the syphons and arch tubes). The N&W faced the same size constraints with the Class A. The only other option was a full water tube boiler, which was shown to be too fragile in the railroad environment.
The first key issue here is heat transfer from the flame/combustion gases to the steel in the syphon, circulator , side sheet or crown sheet - the water can usually be assumed to absorb all the heat absorbed by the steel, one exception is when the temperature of the steel gets so hot as to cause film boiling, e.g. when a crown sheet becomes temporarily uncovered.
The second key issue is that most of the heat transfer from the steel to water is due to localized boiling (nucleate boiling). The faster flow in a circulator or syphon will speed up the process of the seam bubbles moving from the spot they were formed to the top of the liquid surface in the boiler and then to the steam dome.
Page 195 and 196 0f “Allegheny Lima’s Finest”, a caption reads"The highest d.b.h.p. recorded for a C&O Allegheny was 7498 at 46 mph with over 14,000 tons: the highest sustained drawbar horsepower(on the same trip) was 7,375. This performance was in fairly flat territory in South-central Ohio." Further in the caption "Maximum drawbar horse power developed is available for both the N&W A and the C&O H-8, with each road’s own dynamometer car - N&W’s built in 1920 and C&O’s built in 1929. The only drawbar horse power figures for the “A” ever published were obtained in 1936 and were “made with one of these locomotives while handling a merchandise train where the tonnage was relatively low and the speed high.” On level track the “A” tested developed “over 6000 horsepower at speeds from 32 to 57 mph, with a maximum of 6300 hp at 45 mph.”
I hope that sheds some light on the debate. I recommend the book very strongly to anyone looking for info regarding the big three locomotives in question. Some other things to consider are the numbers of the locomotives themselves, and how many other roads used the type. In another section of the book a discussion is made as to which of the designs had the most room for additional gains and clearly the Allegheny could have increased power out put considerably where as the other two were nearly at the limit for the technology of the time. Also the “A” a fine locomotive was not chosen over the C&O’s 2-10-4 when a comparison between the 2 was done by the Pennsy which then built 125 of the texas type to use during WWII.
Factor of adhesion is also quite good for the H-8 as on one occasion an apparent mistake when doubling a train from two yard tracks resulted in an H-8 stalling on the Limeville bridge due to tonnage greatly exceeding it’s capacity. Locomotive did not slip just stalled.
Some day I will make it to one of the museums that have one of the H-8s on display and get to see one in person. I have seen the big boy on display in Dallas
The problem with many of these types of books, is the author makes a statement, but does not link it to a specific, verifiable road test of the locomotive. As Timz and feltonhill has pointed out, many of these tests can not be compared. What is the railroad’s definition of “sustained” HP? Was the drawbar readings corrected for acceleration and/or deceleration? Are were talking about indicated or drawbar HP? Was the locomotive fired in a typical day-to-day economical operating fashion, or was it over fired just to see what it could do?
Without having a citation to a specific road test, and without knowing the specifics on how the test was conducted, it is impossible to verify such statements. On one hand, the author might be spot on. On the other hand, he could just be repeating what someone else told him, or just stating his opinion on the matter.
It is my understanding that N&W borrowed one of the C&O 2-6-6-2’s and they outperformed the N&W Y-1 & X-1. That convinced them to buy the 2-6-6-2. Which must not have been any disappointment at all since they owned so many of them and they lasted till the ending of steam on the N&W.
To get back to the SP cab forwards just briefly, the rated tractive force of the last of the classes, AC-12, was 124,000 according to Robert J Church who wrote the difinitive book on them. I believe their claim to greatness lies in their being such a successful innovation and so well adapted to their purpose rather than their raw power output. One factor that stopped UP from converting more Big Boys to oil firing was the high rate of fuel consumption they experienced with the one engine they did convert. " She just gulped it down" was how one engineman put it. Apparently the coal fire with its thick bed of fuel over the grates had more staying power and stability.
Actually, the AC-6 was the first of the Espee cab-forwards to have the TE increased to 124,000lbs from the earlier AC 4/5 4-8-8-2’s at 116,000lbs. The AC 6 was the last ‘flat-faced’ AC, but it was the first to have the ‘talking’ pumps built onto the smokebox front, and the newer style Worthington FWH. Though it kept both the ‘spoked’ drivers and the Hicken semi-vanderbuilt tender of the two earlier AC classes, it was the true ‘transitional’ AC. After the AC-6, all AC’s were built to specifications of 124,000 lbs. TE, even the ‘cab backward’ AC-9 from Lima.
Though almost every class of AC from Baldwin contained further and further improvements as far as locomotive design was concerned, the TE remained at 124,000 lbs., which was quite sufficient for SP. From the AC-7 on, with the improved balance of the Baldwin disc drivers, they were also designed for 70mph maximum, and on some of the more level sections of the Espee’s trackage, had no trouble achieving it.
You’re right, Church’s book is superb. Another very good book on the subject is George Harlan’s THOSE AMAZING CAB-FORWARDS, first published in 1983. I don’t know whether or not it’s still in print, but it’s definitely worth searching for, IMO. It has some excellent information on the early MC series 2-8-8-2 and the MM series 2 (later 4)-6-6-2’s, also.
Those incredible locomotives were part of my childhood up in Truckee, CA. I have great memories of them. Heck, until I was 10, I thought ALL articulateds ran cab-first, LOL!
N@W class A J and Y6B had boiler pressures of 300 pounds at popoff during RR operation! PRRQ2 4464 duplexes on PRR tests on in house HP tests was almost 8000 horsepower, higest HP of any American steam locomotive except possibly the S2! The N@ W and the PRR designed and perfected their own locomotives for their own service needs, the class A was a very remarkable 6 coupled locomotive and produced more power TE than any challenger type built, the 6300 HP rating was also accurate under actual road performance!