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!
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 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.)
“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.
Isn’t much question that the evolved 2-6-6-4s had significant advantages over Challengers (the only real ‘superiority’ being the supposed better guiding of an Adams-style four-wheel engine truck) and by the time of the Alleghenies the issue was beyond much rational ‘disagreement’.
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?
Because it doesn’t have that much more weight on drivers, you mean. Well, yes, can’t pull hard without weight on drivers.
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.
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:
The same driving axle load (67 500 lb)
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.
No perceptible difference in whole locomotive and front engine unit stability at any speed,
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?
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.)
How 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.
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!
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! [(-D]
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.
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.
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 Retai