Hello all! I've had this question in my mind for quite some time, and after lurking on the forums for a turn I figured it's time to go ahead and ask it. I am curious as to how the 4-6-6-4 "Challengers" used by various roads compare to one another. While the Challengers of the Union Pacific seem to get their share of recognition, those used by other roads, the NP, WP, D&H, etc. Challengers seem to go forgotten.
How did these other 4-6-6-4's stack up to those of the UP, was there a clear "best" among them? 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? Were there any notably poor performers amonst the group? Any and all input/feedback would be much appreciated, if only to give some more recognition to these often overlooked (imho) locomotives!
II Phrogswas there a clear "best" among them?
Was there? Unlikely. Is there? No, no chance anyone now knows enough about them to even guess at which was "best" overall. Or worst.
Fans like to pronounce upon things like that, but none of them knows anything about what each engine cost to run. For all we know, an engine that looks bad to fans might have been low-maintenance, and fans have no way to find that out.
Likewise, us fans today can't compare legendary French compounds to American counterparts. We don't know how the costs would have compared.
UP is best known for being the first to use them and therefore naming the type, and also used them on both freight and passenger trains.
UP owned 105 of the total of 252 4-6-6-4 types ever constructed.
Northern Pacific was next with 47 Challengers and Delaware & Hudson owned 40.
steamlocomotive.com has extensive comparative data.
UP RR #3985 was a favorite of mine: I've been lucky enough to see it in operation on a number of occasions;l In Ks. Ok, Ar, and in Tn, Ky, and on its trip East to run as Clinchfield 676 for Christmas season of '92-'93 (parts of which are available as You Tube Videos.)
Posters might find this linked site of interest.
https://www.trains.com/ctr/railroads/locomotives/most-successful-articulated-locomotive-the-4-6-6-4-challenger/
Article is of a TRAINS article; but the site carries Classic Trains advo.
By Kevin P. Keefe | February 1, 2023.
"These mid-century brutes could move tonnage at up to 70 mph"
Listed article has manufacturing info, number built, and railroads that owned them. [ P.S. That CRR #672 was purchsed from D&H, and/or DRG&W] #676 was to have been the last CRR# of its' 4-6-6-4's
FTA:"...The answer was the 4-6-6-4 Challenger, devised by Alco’s engineers and UP Chief Mechanical Officer Otto Jabelman and featuring an unusually high power-to-weight ratio thanks to its large 132-square-foot grate area, boiler pressure of 280 psi, and relatively small 21 x 32-inch cylinders. The two articulated engines together could muster 97,352 pounds of tractive force and were regularly called upon to operate at speeds up to 70 mph..."
"...The railroad introduced the 4-6-6-4 Challenger with an order for 15 engines in 1936, followed by four more orders 1937-1944, for a total of 105. All the Challengers featured most of the advances of the era, including one-piece cast frames and roller bearings on all axles. The use of 69-inch driving wheels made the Challenger truly a dual-service engine, suitable for use on passenger trains, notably the Portland Rose. Among the engines used in passenger service was No. 3976, painted in UP’s two-tone gray scheme with yellow striping and equipped with smoke deflectors...
A measure of the 4-6-6-4’s success is the fact that eight other railroads went on to acquire Challengers after the introduction of the type on UP. By comparison with UP’s 105 Challengers, the second-largest group was on Northern Pacific, 47 engines, acquired in three groups between 1936 and 1944. The NP engines were bigger and heavier than the UP versions, mostly because of the huge 152-square-foot fireboxes required for use of NP lineside supplies of lower-quality sub-bituminous coal. All the NP Challengers were later converted to oil...
Other railroaders fielding Challengers included the Clinchfield, with 12 engines, six of them acquired second-hand; Delaware & Hudson, with 40; Denver & Rio Grande, with 21, six of which went to the Clinchfield; Spokane, Portland & Seattle with eight, two of which later went to Great Northern; Western Maryland, with 12; and Western Pacific, with seven. Nearly all the Challengers were built by Alco, with the exception of Baldwin engines on D&RGW and WP...."
Personally, I disagree with Mr. Keefe. I'm sure a lot of N&W fans do too!
.
You're probably being too generous when you say there was something in that article to disagree with.
timzYou're probably being too generous when you say there was something in that article to disagree with.
Not that I dislike Challengers, mind you. The D&H engines in particular changed the whole game for D&H operations.
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?
II Phrogsin 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
Saying "surprisingly low adhesive factor" is exactly the same as saying "surprisingly high calculated tractive effort". N&W thought they could get away with largish cylinders; maybe they assumed their engineers were good at coping with slipping. Maybe they were right -- none of us fans knows.
Incidentally, N&W's calculated tractive effort for the A might have been conservative. The A had limited cutoff (75% or so) so in its TE calculation N&W only assumed 77% mean effective pressure.
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.
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?
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.)
It'll a bit annoying but it goes away as soon as the moderators realize you're the real deal
Same me, different spelling!
II Phrogs[N&W's 2-6+6-4] was found quite wanting on grades in excess of 1%?
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!
Here is a picture of Challenger 3935 on Train 717 The Los Angeles Challenger in 1940.
https://www.railpictures.net/photo/850086/
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.
More proof of the lack of standardization in steam.
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.
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.
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.
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.
Never too old to have a happy childhood!
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?
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!
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!
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.
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
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.
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?
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?
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.
Well, that ain't good
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?
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.
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?
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.
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