Keep in mind that the effective tube/flue length in any modern boiler is in the range of 20 - 24'. Anything longer than that is a waste, even if used in a Chapelon or Porta sectional arrangement.
The issue with burning subbituminous 'correctly' is that the fuel is extremely friable, and breaks up and levitates in the combustion plume. You will see ignorant railfans saying something like "40% of the coal never hits the grates" and indeed it doesn't, but it burns similar to carbureted oil, with some of the same luminous-flame advantage that oil has.
In order to get this effect with a typical 'deep' firebox, you would need a method of firing either capable of placing fuel far down under the arch, or feeding at the throat as many methods of oil firing do to get the longest plume. In practice that would be more difficult than the methods used on Challengers.
There are a couple of presumptions: that the lavish amount of fuel to produce equivalent mass flow of steam is available, and that the net cost of all the fuel is lower than bituminous or oil. A more important consideration (since 1970, nearly a decade after it ceased to matter on UP) is the extraordinarily dirty exhaust from that method of firing using nothing more complicated than a regular stoker arrangement for control. Careful tinkering with the secondary-air arrangements and providing effective combustion-air preheat might go a long way toward addressing this stuff.
You wouldn't fire an A on subbituminous or any other low-rank coal; it wasn't designed for that. It might be said that the Allegheny could be run on lower-quality coal -- but I suspect it, too, would not do well. That might be different if you arranged to feed the fuel from the throat, something that was the subject of a great deal of development in the late Thirties (and that, as discussed in a couple of other threads, might have been one of the great epic failures of steam technology in practice...)
Of course, there is a better answer: the Garratt. That gives you unhindered access to a grate that can be as low and wide as your loading gage permits, combined with a barrel diameter uncompromised by driver or frame height and adequate room for multipass Franco-Crosti economization, effective air preheat, etc. A couple of 2-6-6-2 engines and you have everything a large engine could want for...
Forgive my ignorance but would a deep firebox as described be just as useful when using the lesser quality coal utilized by many of the roads that employed Challengers? I was under the impression that the shallow firebox was necessary to increase volume to make up for the lower-energy coal being used, and as such were a necessary compromise.
For the sake of discussion how would a N&W A run using UP Sub-Bituminous coal, or in an even more extreme case Northern Pacific Rosebud coal? Conversely, how would a wide, shallow firebox Challenger run using the high BTU coal used on the N&W?
There are a number of references, none yet quite rigorous, which point out the superiority of a proper deep firebox with circulators over something with a wide grate 'over the drivers'. This is further enhanced if active circulation is provided in the water legs (a la Cunningham circulator, which draws from a downcoming region in the convection section of the boiler, and uses a jet pump to distribute it through nozzles in the outer wrapper above the mud ring).
The deep firebox implies greater mass on the trailing truck, both from the additional metal structure and weight of water. Note that on C&O, which had dramatically high axle-load capacity, the Alleghenies have a six-wheel trailing truck.
Rear-end stability on a deep-firebox engine of suitable capacity is almost incomparably better than a Challenger. Look at the Bissel formula that keeps the truck wheelbase 'normal to the railhead' in curves, then extend the truck out so rear bearing and steering forces are as far outboard and to the rear of the chassis as possible, and angle the restoring-force devices (usually rockers or segments of gears) to match the swing radius at the rear.
In a pinch, you could use the dodge that was introduced in the 'intermediate' Berkshire trailing truck frame, when a long frame pivoted at the original 'articulation' point was used as a Delta-style trailer. This was treated dynamically as a long 2-wheel Delta trailer, with the leading axle only weight-bearing -- it could float laterally on a pair of hardened-steel rollers independently of truck-frame angularity. Any of the subsequent schemes of lateral-motion compliance could be used on such an axle if desired.
The only American engines with a deep firebox and divided drive that used a four-wheel lead truck were the PRR Qs, and those did not have the 'compound-pendulum' guiding concerns of a Mallet-style chassis. All the six- and eight-coupled simple articulateds with deep fireboxes used some form of two-wheel Bissel lead truck, and in at least one situation (the B&O EM-1s in M&E service) this caused a service-speed reduction -- I do not know whether this was actually based in engineering analysis or just advisory/CTA. The primary reason for the two-wheel truck is simple: it reduces the overall length of the engine at the front, rather than by siamesing the firebox over the drivers at the rear; a secondary reason is that all four mains can be the same dimensions for balance without needing to resort to an extended piston rod and crosshead guides a la PRR T1.
We need not look further than the N&W A (and the late Y-class) for a 'correct' two-wheel high-speed lead truck. It could be argued that LS&MS had some careful design on their 2-6-2s (which were supposed to be among the world's fastest engines when introduced), and that New York Central kludging them into rather inferior Pacifics after the disaster with Wilgus' "1-D-1"s having to have four-wheel engine trucks shoehorned under them was 'unnecessary surgery' from an actual dynamic performance point of view -- but I do not know for sure either way.
Certainly the A was good for 70mph as designed, and I strongly suspect the last 5 (with the lightweight rods) had some 'breathing' done on their lead trucks for better curve entry and mitigation of leading-driver-pair flange forces (the mass of the chassis being considerably less than that of a conventional locomotive with the same truck and driver spacing).
You run into the same overweight problem with any real high-speed articulated just as Lima did with the Allegheny/Blue Ridge types: the weight is in the high-capacity streamlined steam and exhaust piping arrangement, and this would apply to a proper Challenger. We note that for high-horsepower high-speed designs, nothing more than six-coupled engines are used -- there is no particular reason why you couldn't make a ginormous 2-8-8-x with 76" drivers except that it would be too long, relatively heavy, and possess a diabetic water rate requiring auxiliary tenders to get even mediocre range between water fills. Any single-unit steam locomotive, reciprocating or turbine, hits that limit somewhere around 8000dbhp, and of course many hit it before. This, for example, is why we all laughed so hard at the railfan version of Chapelon's Big Boy 'improvement regimen' that would have it producing "10000hp" or greater -- even with proper Chapelon compounding and American detail design for high thrust, you'd have no fun running it at that power.
For fun, start with the rough dimensions of a N&W A (or Seaboard R-2) and give it a double-Belpaire chamber. This would give you up to 76" potential driver diameter to play with, but I wouldn't go above 72" or so with modern dynamic balancing and thin-section rods. Use the Allegheny piping dimensions, with some reasonable boiler pressure that doesn't cause ridiculous maintenance requirements (this would likely still be somewhat south of 300psi, and certainly no higher!) and carefully design your chests and valve size to optimize high-speed flow. (You will definitely want reversible compression control on the forward engine, and that indicates you'd likely want it on all four cylinders). With proper Snyder combustion-air preheating and Cunningham circulation, this might keep the required firebox+chamber dimensions in line with what a four-wheel truck could bear, and the corresponding grate area might make the engine more flexible to fire at less than full load.
Pneudyne Maybe look at the 4-6-6-4 vs. 2-6-6-4 comparison this way: Start with the UP “big” Challenger of 1942 as a baseline. Then design a 2-6-6-4 (or 2-6-6-6 if needs be) within the following constraints: 1. The same driving axle load (67 500 lb) 2. Lateral railhead forces (during curving and arising from restraint of yaw oscillation) no higher at any speed, recalculating the 4-6-6-4 for any lateral control improvements developed for the 2-6-6-4 case that could also be applied to the 4-6-6-4. 3. No perceptible difference in whole locomotive and front engine unit stability at any speed, 4. The same factor of adhesion. What then would be the likely advantages conferred by the 2-6-6-4 (or 2-6-6-6), realizable in daily service? (I don’t know the answer, by the way.) Cheers,
1. The same driving axle load (67 500 lb)
2. Lateral railhead forces (during curving and arising from restraint of yaw oscillation) no higher at any speed, recalculating the 4-6-6-4 for any lateral control improvements developed for the 2-6-6-4 case that could also be applied to the 4-6-6-4.
3. No perceptible difference in whole locomotive and front engine unit stability at any speed,
4. The same factor of adhesion.
I thought this was an interesting set of questions and wanted to revisit it to see if anyone with more knowledge on the subject has any answers? I feel that discussing and finding answers to specific questions such as these challenges (hehe) people to push beyond their natural biases and overcome the usual "well this locomotive is clearly best since it ran in the same geographical location that I happen to be from"!
Bringing this thread back a little bit, does anyone have the unit costs of these? I've seen some numbers thrown around for NP Z-6's (185,000 ish) the UP CSA-1's (130,000 ish) and the last UP Challengers (225,000 ish) but apart from the Z-6 I dont really have faith in these numbers. Would be interesting to see how costs stack up.
UP 'Small'
RA
1936 December 19
pp.900-903
RME
1937 January
pp.1-7
NP
1937 March 06
pp.389-391
1937 April
pp.160-163
DRGW
1938 July 09
pp.42-44,70
1938 September
pp.323-329
D&H
1940 August 10
pp.207-218
1940 September
pp.337-344
WM
1941 January 25
pp.209-215
1941 February
pp.45-52
UP 'Big'
1942 October 03
pp.516-519
1942 October
pp.413-417
As I think is well-known, both journals are available at the Internet Archive, RME under its later name of ‘Railway Locomotives and Cars’.
https://archive.org/details/pub_railway-age?sort=-date&and%5B%5D=year%3A%221937%22
https://archive.org/details/pub_railway-locomotives-and-cars
II Phrogs How did the relatively poor quality coal used by the Northern Pacific impact their performance, and by extension did the conversion to oil for the SP&S locomotives give any advantage or boost to their performance?
How did the relatively poor quality coal used by the Northern Pacific impact their performance, and by extension did the conversion to oil for the SP&S locomotives give any advantage or boost to their performance?
II Phrogs Pneudyne Just wanted to say thank you, this was both a highly informative and entertaining read and gives a good understanding of. the differencies and similarities between the various Challenger designs. If I am remembering correctly, I believe the D&RGW used a handful of the later Alco designed Challengers which were diverted from a UP order to make up for a shortage in motive power on the D&RGW during the war. To your knowledge, how did these UP Challengers fare in service on a different railroad? From what I've read the D&RGW wasn't particularly enamored with these locomotives. Was this due to any inherent flaw in their design, or was it more that the Challengers were delivered in lieu of the FT diesels that many roads were trying to get their hands on around this time? Is there any data or testimony on how these locomotives stacked up to the Baldwin 4-6-6-4's already in use on the D&RGW?
Pneudyne
Just wanted to say thank you, this was both a highly informative and entertaining read and gives a good understanding of. the differencies and similarities between the various Challenger designs.
If I am remembering correctly, I believe the D&RGW used a handful of the later Alco designed Challengers which were diverted from a UP order to make up for a shortage in motive power on the D&RGW during the war. To your knowledge, how did these UP Challengers fare in service on a different railroad? From what I've read the D&RGW wasn't particularly enamored with these locomotives. Was this due to any inherent flaw in their design, or was it more that the Challengers were delivered in lieu of the FT diesels that many roads were trying to get their hands on around this time? Is there any data or testimony on how these locomotives stacked up to the Baldwin 4-6-6-4's already in use on the D&RGW?
Rio Grande had originally wanted to order some additional Baldwin 4-6-6-4's. The war production board would not do so and diverted some from a UP order. The Alco UP design challengers diverted to the Rio Grande were on lease from the War Production Board. The Rio Grande crews did not like them. From what I remember reading (but I can't remember the source and was trying to find it) the crews found the pullling power lacking along with the ride qualities compared to the Baldwins. I am trying to remember but it seems like they may have had some issues with the centipede tenders. UP and Rio Grande approaced their usage of challengers a bit differently. UP tended to run higher speeds- Rio Grande slower and longer trains. After the war the Alcos were given back to the War Production board and would up beind sold to the Clinchfield.
I have no insight on how they were viewed by the line, but Trains reported at the time that the Rio Grande returned them to the War Assets Administration since they were surplus to their needs with the postwar traffic decline and they didn't want to purchase them.
Well, that ain't good
Conductor_Carl... On a subject change, I feel like I have heard of the Western Maryland Challengers being a cut above. Something to the effect of them being higher horsepower than the others?
On a subject change, I feel like I have heard of the Western Maryland Challengers being a cut above. Something to the effect of them being higher horsepower than the others?
Read in a book about the WM, the operating costs of their Challengers was such that the WM parked them several year BEFORE their equipment trusts expired - thus WM found it to their advantage to pay on the equipment trust without using the equipment that the trust was for.
Never too old to have a happy childhood!
Comparing the different Challengers may be a bit hard as they are geographically far flung enough that their usage may vary, and what works for the Northern Pacific may not be applicable to the Delaware and Hudson.
I think that there are two ways that you could cut this to be interesting.
1. Look at the usage of the UP challengers on the Rio Grande and Clinchfield. If they worked essentially just as well on all three roads then that is a lot of geographical distance and perhaps different usage covered by one loco type and would speak to a universal quality.
2. Compare the UP Challengers on the Rio Grande to the Rio Grande Challengers. This compares two the two different Challenger different builders (ALCO and Baldwin) on essentially the same road and conditions.
Great Northern also owned two Z-6 oil-fired Challengers that were bought from subsidiary Spokane, Portland & Seattle that were numbered 4000 and 4001.
Eventually as it dieselized the Great Northern sold them back to SP&S.
But Great Northern is not typically though of as a Challenger owner but it was in the 4-6-6-4 club!
https://www.deviantart.com/avalanch11/art/Great-Northern-4-6-6-4-4000-Steam-Locomotive-996878578
BigJim I would suggest that you try to find and read a copy of Eugene L. Huddleston's book "The World's Greatest Steam locomotives". In this book Mr. Huddleston compares the "Allegheny", the Class A, and the Challenger. Plus, some other tid-bits!
I would suggest that you try to find and read a copy of Eugene L. Huddleston's book "The World's Greatest Steam locomotives". In this book Mr. Huddleston compares the "Allegheny", the Class A, and the Challenger. Plus, some other tid-bits!
Many thanks for the reading suggestion, I am ever on the prowl for a new book to expand my collection/knowledge and will certainly look into acquiring a copy of this one! Additonally thank you and others for the responses regarding the Class A 2-6-6-4's, I do hope I did not come off as disparaging these fantastic locomotives, I wish only to expand my understanding of these fascinating machines.
If I may turn back to my initial question and request your and others knowledge on the subject, I have one standing question in regards to the Z-8 Challengers of the NP and SP&S. As I understand it, the SP&S challengers were converted to burn oil, however kept the gargantuan fireboxes of the original NP design. Would this conversion to oil have any appreciable impact on the performance of the locomotives? What differences might one expect going from burning the incredibly low quality coal used by the NP to burning oil? Any insight into this is greatly appreciated.
II Phrogs May I ask what advantages those might be? The only inherent disadvantage of the 4-6-6-4 when compared to the 2-6-6-4 that comes to mind (though I am not in any way an expert on the subject, hence my curiosity) is the shallow firebox of the Challengers, which extends over the rear drivers. While, at least in the case of the N&W A Class, the 2-6-6-4 seems to produce a fair bit more tractive effort, it also seems to have a surprisingly low adhesive factor, would that not balance things out in the end?
May I ask what advantages those might be? The only inherent disadvantage of the 4-6-6-4 when compared to the 2-6-6-4 that comes to mind (though I am not in any way an expert on the subject, hence my curiosity) is the shallow firebox of the Challengers, which extends over the rear drivers. While, at least in the case of the N&W A Class, the 2-6-6-4 seems to produce a fair bit more tractive effort, it also seems to have a surprisingly low adhesive factor, would that not balance things out in the end?
.
Erik_MagDiesel locomotives can produce close to rated horsepower at any speed from the speed at which maximum continuous tractive effort to somewhere near maximum rated speed. Furthermore, by simply changing the gear ratio, a given locomotive mode can be set up for drag service or high speed service. Finally, diesel locomotives can be M.U.'ed so it is simple to lash up just the required number of units to haul a train. Fuel is pretty much the same for all RR's. Steam locomotives are much less flexible, requiring different designs for flat land running versus mountain hauling, hauling long trains versus short trains, etc. Fuel could be high quality bituminous, lignite or bunker C, each requiring different firebox designs. To be fair, lack of standardization in steam was driven by hard requirements as well as the whims of the various mechanical departments.
Steam locomotives are much less flexible, requiring different designs for flat land running versus mountain hauling, hauling long trains versus short trains, etc. Fuel could be high quality bituminous, lignite or bunker C, each requiring different firebox designs.
To be fair, lack of standardization in steam was driven by hard requirements as well as the whims of the various mechanical departments.
One overlooked area of the differences between steam and diesel. Steam engines, besides containing the air compressors and the brake valve - did not factor into the braking equation for the train it was hauling. Using he Independent brake would bring the brake shoes in contact with tires on the drivers. The tires had been heated to create a shrink fit with the driver wheel when the tire cooled. If too much Independent brake was used the tire(s) could expand from the heat and leave the driving wheel.
Diesel have the use of Dynamic Brakes to retard the movement of the train and thus the locomotives become a bigger factor in the braking of trains, especially in mountainous territory..
In steam days the Retainer Valves had to be manipulated by the crew to 'reatin' brake applications for a period of time while the trainline was being recharged after a brake application was released. Setting the Retainers up or down was a manual fuction performed by the brakemen on a train.
Diesel locomotives can produce close to rated horsepower at any speed from the speed at which maximum continuous tractive effort to somewhere near maximum rated speed. Furthermore, by simply changing the gear ratio, a given locomotive mode can be set up for drag service or high speed service. Finally, diesel locomotives can be M.U.'ed so it is simple to lash up just the required number of units to haul a train. Fuel is pretty much the same for all RR's.
More proof of the lack of standardization in steam.
timzHow wanting? PRR tested the A, but none of us has any idea what tonnage it pulled on what PRR grades, or failed to pull. PRR decided not to bite, but none of us knows why.
I've said this before and I'll say it again. I have no way of proving this but I suspect the PRR (with Baldwin looking over their shoulder) after testing an N&W Class A ( and Class J for that matter) didn't want to admit those "hillbillies" down in Roanoke were better at steam locomotive design than they were!
Corporate ego may not have played a role here but I wouldn't discount it entirely. The PRR didn't call itself "The Standard Railroad Of The World" for nothing!
Just a "might have been" to think about. Post-WW2 and flush with money and not having bought any new steam locomotives since 1930 the Jersey Central was considering buying Challengers for their coal drags but not for long. In the end they bought F3 diesels.
Here is a picture of Challenger 3935 on Train 717 The Los Angeles Challenger in 1940.
https://www.railpictures.net/photo/850086/
II PhrogsWhat of testing done on the Class A by other railroads when tested (I believe it was the PRR, but feel free to correct me), where it was found quite wanting on grades in excess of 1%?
No need for other RR's. Just listen to any of the actual recordings of the Class A's on the Blue Ridge grade, which by the way is in excess of 1%, and you will find that they are quite surefooted! Then, go find out what kind of tonnage they hauled on the way out of Williamson, WVa or Crewe, Va. I am sure that you will find that you need to do tons more researching before you go jumping to conclusions!
II Phrogs[N&W's 2-6+6-4] was found quite wanting on grades in excess of 1%?
It'll a bit annoying but it goes away as soon as the moderators realize you're the real deal
Same me, different spelling!
BigJim You only need to look at the performance of the Class A's hauling coal west and east to see that the factor of adhesion was not a problem.
You only need to look at the performance of the Class A's hauling coal west and east to see that the factor of adhesion was not a problem.
What of testing done on the Class A by other railroads when tested (I believe it was the PRR, but feel free to correct me), where it was found quite wanting on grades in excess of 1%?
This is the exact reason I have always been a big fan of the Challengers (and why I wanted to know more about their differences across the various roads which used them!). They have always struck me as incredibly well balanced locomotives, being relatively fast and powerful, but not at the expense of adhesion to the rails. They were used by quite a number of railroads and as a result encountered a variety of running environments/conditions. On top of all this, they did it all using some of the poorest quality coal out there, unlike some locomotives which required a more pampered diet of only "top shelf" coal.
(unrelated, but I hope I included the quote correctly. I'm still getting used to using the forums and due to the wait time between submitting my reply and having it approved it's taking me some time to figure out the details.)
II PhrogsWhile, at least in the case of the N&W A Class, the 2-6-6-4 seems to produce a fair bit more tractive effort, it also seems to have a surprisingly low adhesive factor, would that not balance things out in the end?
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