feltonhill I found a lecture presented by Robert M. Pilcher 3/12/53, at that time Assistant Engineer of Tests for N&W. He had this in his script: "Under unusual spot conditions dynamometer records a maximum sustained horsepower of 6300 at 45 mph." [He did not specify boiler pressure for this reading, but other sources indicate that it was 275 psi. No test report has been found yet] "In usual day to day operation, the dynamometer record indicates drawbar horsepower between 5200 and 5400 over long distances at speeds between 35 and 40 mph while handling 175 loaded trains over almost level track." These figures occur frequently in N&W public statements and articles written in the 1940s-50s.
I found a lecture presented by Robert M. Pilcher 3/12/53, at that time Assistant Engineer of Tests for N&W. He had this in his script:
"Under unusual spot conditions dynamometer records a maximum sustained horsepower of 6300 at 45 mph." [He did not specify boiler pressure for this reading, but other sources indicate that it was 275 psi. No test report has been found yet]
"In usual day to day operation, the dynamometer record indicates drawbar horsepower between 5200 and 5400 over long distances at speeds between 35 and 40 mph while handling 175 loaded trains over almost level track."
These figures occur frequently in N&W public statements and articles written in the 1940s-50s.
Jim--
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!
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!
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.
UP 4-12-2 According to Huddleston, the USRA 2-6-6-2 was regarded, even during its era, as nearly a "failure" in comparison to the much more successful and powerful USRA heavy mallet 2-8-8-2. Only 2 railroads bought them, and even though C&O built 10 late copies, they were primarily to replace worn-out locomotives on mine branch line service--where they were ideally suited.
According to Huddleston, the USRA 2-6-6-2 was regarded, even during its era, as nearly a "failure" in comparison to the much more successful and powerful USRA heavy mallet 2-8-8-2. Only 2 railroads bought them, and even though C&O built 10 late copies, they were primarily to replace worn-out locomotives on mine branch line service--where they were ideally suited.
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.
.
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?
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 and it is quite impressive.
feltonhillSo, 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!
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!
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.
- Erik
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.
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%.
erikemfeltonhillThe N&W Class A had 530+57 SF (firebox+circulators) of direct heating surface vs the J's 518+60 SF of DHS, relatively close. These are as-built figures for 1200-1237. The A relied more on its indirect HS, which was significantly larger than the J (6,063 vs 4,693 SF). The final order of A's were equipped with six circulators as built instead of arch tubes. Based on photos, at least 15 of the older A's were retrofitted with circulators. There may have been more.Something about circulators, arch tubes and syphons has always bothered me. By industry standards, they are considered part of direct heating surface and are used to estimate DHS evaporation. Yet I've always wondered if they have the same heat transfer capability as the firebox sheets. It seems that the water velocity through these additions would be very rapid, much more so than the water surrounding the firebox. Could it be that arch tubes, circulators and syphons are "less equal" than firebox sheets in terms of heat transfer per unit time? Circulators and arch tubes have a relatively small contribution to DHS, but syphons have a much larger effect. If so, locomotives equipped with syphons would seem to have a falsely large advantage over those equipped with circulators as far as estimated evaporative capacity is concerned. Anyone know if this is the case? 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.- Erik
feltonhillThe N&W Class A had 530+57 SF (firebox+circulators) of direct heating surface vs the J's 518+60 SF of DHS, relatively close. These are as-built figures for 1200-1237. The A relied more on its indirect HS, which was significantly larger than the J (6,063 vs 4,693 SF). The final order of A's were equipped with six circulators as built instead of arch tubes. Based on photos, at least 15 of the older A's were retrofitted with circulators. There may have been more.Something about circulators, arch tubes and syphons has always bothered me. By industry standards, they are considered part of direct heating surface and are used to estimate DHS evaporation. Yet I've always wondered if they have the same heat transfer capability as the firebox sheets. It seems that the water velocity through these additions would be very rapid, much more so than the water surrounding the firebox. Could it be that arch tubes, circulators and syphons are "less equal" than firebox sheets in terms of heat transfer per unit time? Circulators and arch tubes have a relatively small contribution to DHS, but syphons have a much larger effect. If so, locomotives equipped with syphons would seem to have a falsely large advantage over those equipped with circulators as far as estimated evaporative capacity is concerned. Anyone know if this is the case?
Something about circulators, arch tubes and syphons has always bothered me. By industry standards, they are considered part of direct heating surface and are used to estimate DHS evaporation. Yet I've always wondered if they have the same heat transfer capability as the firebox sheets. It seems that the water velocity through these additions would be very rapid, much more so than the water surrounding the firebox. Could it be that arch tubes, circulators and syphons are "less equal" than firebox sheets in terms of heat transfer per unit time? Circulators and arch tubes have a relatively small contribution to DHS, but syphons have a much larger effect. If so, locomotives equipped with syphons would seem to have a falsely large advantage over those equipped with circulators as far as estimated evaporative capacity is concerned. Anyone know if this is the case?
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.
Feltonhill, As Erik pointed out, rapidly flowing water is much better for heat transfer. This is why the water pump in a car engine runs as such high speed. I am still quite surprised the Class A's relatively small direct heating surface. Heat transfer is exponential in nature for radiative (direct) heating surfaces vs. linear for convective (indirect) heating surface. A modest increase in direct heating surface will pay huge dividends in steam production, while a large increase in indirect heating surface pays little.
Relying on large amounts of indirect heating surface (IHS) has other issues as well. A locomotive boiler can only be so big and still fit into a railroad's loading gauge. The way to increase IHS is to use longer, smaller diameter tubes. The only way to increase the length of the tubes, and still keep the overall boiler length the same, is to decrease the length of the combustion chamber (which is direct heating surface). The increased length of the tubes would also decrease the efficiency of exhaust gas flow to the stacks. The smaller diameter of the tubes presents problems of maintaining enough oxygen to allow complete combustion. The temperature gradient across the tubes from back to front will encourage condensation of combustion gasses in the tubes which is very bad from an efficiency point, plus it allows corrosive byproduct to accumulate in the tubes. It is much better for the gasses to fully burn in a larger combustion chamber that will absorb the radiative heat, and have shorter, larger diameter tubes to exhaust the spent combustion gas as quickly as possible
This design change can clearly be seen in the late steam era. ALCO did it with the NYC 4-8-4 Niagara, Lima did it with the C&O 4-8-4 J3a. Lima not only changed the tubes to 4" diameter, but they shortened the tube section and correspondingly lengthened the combustion chamber compared to the earlier J3. Baldwin did it with the B&O 2-8-8-4 EM1, which may be the most dramatic example. For a locomotive with the boiler length of the EM1, the 4" diameter fire tube section was barely 20' long. In comparison, the firebox / combustion chamber ran from the firebox doors in the cab, clear up to the rear axle of the front (!) set of drivers. The EM1's direct heating surface was supported by 7 axles -- the 2 rear trailing axles, the 4 rear drive axles, and the 4th drive axle of the front engine. Back in the 1970's, old B&O engineers told me that an EM1 may run out of adhesion on a hard pull, but they never, ever ran out of steam at speed. No wonder, they were a giant combustion chamber on wheels!
I'm sure this wasn't lost on the N&W in the late steam era. I suspect by the time the last A's were constructed, the "handwriting was already on the wall" as far as the future of steam was concerned. Probably made no economic sense to totally redesign the Class A to late steam specification, so they did some upgrades (additional circulators) and called it a day.
feltonhillSomething about circulators, arch tubes and syphons has always bothered me. By industry standards, they are considered part of direct heating surface and are used to estimate DHS evaporation. Yet I've always wondered if they have the same heat transfer capability as the firebox sheets. It seems that the water velocity through these additions would be very rapid, much more so than the water surrounding the firebox. Could it be that arch tubes, circulators and syphons are "less equal" than firebox sheets in terms of heat transfer per unit time? Circulators and arch tubes have a relatively small contribution to DHS, but syphons have a much larger effect. If so, locomotives equipped with syphons would seem to have a falsely large advantage over those equipped with circulators as far as estimated evaporative capacity is concerned. Anyone know if this is the case?
UP 4-12-2He [Huddleston] 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,
UP 4-12-2and he added that they wanted to do that at 25 mph.
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".
Just my guess.......
timz 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?
...Do not know what he would say, I say 15mph%1.14 with 4000tons, 1hr sustained...
lars
UP 4-12-2I'm confused.
UP 4-12-2, @all
here is the original text...
page 39:From a steaming standpoint, the 4005 steamed betterthan any oil burning power UP men hadseen on the road. However, the single burnercaused spot heating on the huge crown sheetwhich in turn, caused it to leak. Every trip was the same - when you lookes in the fireboxit was just like a rainstorm, with water poringdown 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....
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.
John
UP 4-12-2According to Huddleston, UP's design goal was to achieve 25 mph unassisted on the Eastbound average 1.14%, 24 mile grade over the Wasatch
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?
GP40-2 to my knowledge, no records exist of a Class A producing 6,300 HP.
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.
(And yes, he said the engine was 275 psi.)
I'm confused.
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?
Help me out here, please.
Thanks.
UP 4-12-2 Kratville also says in his books the Big Boys were more difficult to fire than the Challengers. Also, when converted to oil, the Big Boy (#4005) did not perform very well at all, whereas the Challengers converted easily to oil and steamed quite well. John
Kratville also says in his books the Big Boys were more difficult to fire than the Challengers. Also, when converted to oil, the Big Boy (#4005) did not perform very well at all, whereas the Challengers converted easily to oil and steamed quite well.
When converted to oil, Kratville says they were steaming best. The leaking problem was another one, but not the steaming capabilities.
feltonhillSomething about circulators, arch tubes and syphons has always bothered me. By industry standards, they are considered part of direct heating surface and are used to estimate DHS evaporation. Yet I've always wondered if they have the same heat transfer capability as the firebox sheets.
Didn't the UP steam-crew removed some of the T-circulaters of 3985 firebox without any known power loss? Hard to say for me, if these are anyway valuable in a oil-burning firebox.
For Valeriy:
here you may find some notes about the Virginian AE and more about its railroad ops...
http://www.catskillarchive.com/rrextra/ngstory.Html
See page 366 ( picture of an AE blasting out of a tunnel )
P. 370 Virginian hauling 17.500t record train in 1921
P. 378 Pic. of the largest iron horse
The AE class set many records:
- most weight on drivers
- largest boiler diameter
- largest low pressure cyl.
- highest starting TE of two coupled artic. engines
Cheers
The N&W Class A had 530+57 SF (firebox+circulators) of direct heating surface vs the J's 518+60 SF of DHS, relatively close. These are as-built figures for 1200-1237. The A relied more on its indirect HS, which was significantly larger than the J (6,063 vs 4,693 SF). The final order of A's were equipped with six circulators as built instead of arch tubes. Based on photos, at least 15 of the older A's were retrofitted with circulators. There may have been more.
Be back later.
Three bits of information stick out here: "under unusual conditions", "no test report has been found", "in usual operation dynamometer records indicates drawbar horsepower between 5200 and 5400"
That's why I made the statement, to my knowledge, no records exist of a Class A producing 6,300 HP. The "under unusual conditions" and "no test report found" raises more questions. There are plenty of N&W sources stating the 5200 to 5400 HP figure however. Who knows, maybe under the right conditions, the A could produce 6000 HP, but I have found no records to indicate it.
What I find interesting, if my data is right, is the Class A didn't have any more direct heating surface than the Class J (580 sq.ft. vs 575 sq.ft) and lacked thermic syphons and circulators. By comparison, the two other large Eastern simple articulated locomotives, the H8 Allegheny and EM1 both had 760 sq.ft. direct heating surface, thermic syphons and circulators. Perhaps feltonhill can comment on this aspect of the A's design.
To the original poster, Valeriy--
If you check the used book market, there are some fine books regarding the various engines you mentioned.
There is a book devoted entirely to the H-7 Class.
There is a book called Northern Pacific Super Steam Era.
There are books by Robert LeMassena. I think the titles are: Articulated Steam Locomotives of North America, Volumes 1 and 2.
Respectfully submitted--
My copy of Huddleston's book is loaned out to a friend, so I can't find the source he may or may not have cited for the 6,300 dbhp figure for the A Class.
Regarding the SP Cab Forwards mentioned above: They were surely great engines, and I'm not sure if the starting tractive effort was high enough to get them onto Huddleston's "top 10". It may have been the engine I left out.
Again--my copy of the book is loaned out, or I could look it up.
Sorry for the confusion.
GP40-2 The N&W never claimed that much HP [6300 dbhp] from an A.
Huddleston states in his book that the Big Boys were more difficult to fire than the Challengers, and it was Huddleston who suggested it seemed the Big Boys were unable to produce quite enough steam at speed on heavy grades. According to Huddleston, UP's design goal was to achieve 25 mph unassisted on the Eastbound average 1.14%, 24 mile grade over the Wasatch--which they apparently did not quite achieve. Eventually, two Challengers with about 70 car train lengths proved to be the ideal choice over that division--till the end of steam.
Even though all the big articulateds had stokers, some were easier than others to fire.
All these large locomotives had automatic stokers, although operating them certainly required skill. I don't think the Big Boys' slowing down on hills had anything to do with a lack of performance. They were rated as more powerful locomotives, thus had longer and heavier trains to pull, and the heavier the train of course the slower the uphill climb. Possibly loading them to their capacity was more routine than with the Challengers.
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