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.
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?
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.
You're probably being too generous when you say there was something in that article to disagree with.
Personally, I disagree with Mr. Keefe. I'm sure a lot of N&W fans do too!
.
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...."
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.
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.
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!
Our community is FREE to join. To participate you must either login or register for an account.