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@Mike CT posted:

(Pennsy), heavy,  I1 decapod would also figure into the conversation. ?? More decapods than any other configuration??  IMO.   Middle shelf, Sunset Thirdrail decapod. Bottom shelf is a Weaver M1a mountain.

That CP 4-6-4 reminds me that PRR was generally light in the Hudson department* as well.  One wonders how they would have referred to 'em; certainly not Hudsons...  ;-)

https://en.wikipedia.org/wiki/...ssification#P:_4-6-4

Mitch

*At least in the steam section of the roster.  The P5 electrics are, of course, legendary. 

Since the 4-8-4 was so successful on other roads, it makes me think that the PRR must have had a specific reason no to employ the design.  It may not have even been technical.  But when you have 4-8-2, 2-10-0 and even 4-4-4-4 styles in play, it seems odd not to have this style (edited).

Last edited by jhz563
@jhz563 posted:

Since the 4-8-4 was so successful on other roads, it makes me think that the PRR must have had a specific reason no to employ the design.  It may not have even been technical.  But when you have 4-8-2, 2-10-0 and even 4-4-4-4 styles in play, it seems odd not to see a Hudson type.

It all boils down to what is needed for the railroad.

ACL, FEC, UP, NP, WP, SP, MP, C&NW and CRI&P didn't have Hudsons either.  Nor did the CB&Q's subsidiaries C&S and FW&D even though the "Q" had them.

Rusty

The progression of PRR Steam essentially came to a halt after the M1 because of electrification.

Two reasons behind this:

1. When the PRR started the electrification of the NYC to Phila. main in the late 20s, they displaced their passenger steam locomotives (mostly K4s) from these lines. This surplus of mainline locomotives on the rest of the system diminished the need for new steam locomotives. More and more steam was displaced as the PRR spread electrification from Phila. to D.C. and later extended from Paoli to Harrisburg. There were so many surplus steam engines that they could doublehead on heavy trains (and the PRR was a big fan of doubleheading to their own detriment). There was essentially no need for new locomotives.

2. Electrification became the big focus for the PRR. In between a period of about 10 years from ~1924-1934, they designed and tested 7 classes of mainline electric locomotives (DD2, O1, P5, GG1, R1, L5, L6)***. Research money was essentially being redirected away from steam, and the PRR liked to design in house so it would be unlikely that they would buy a standard design from Baldwin or Lima.

***As a side note, the O1 (4-4-4) was designed to be the electric equivalent of the E6 while the P5 (4-6-4) was designed to be the equivalent of the K4... performance of the locomotives was not as good as the PRR desired on longer trains therefore the O1 was mostly used on shorter (non priority) trains. The subpar performance of the P5 sent the PRR back to the drawing board (leading to the GG1). The P5 was re-geared for freight service once the GG1s were designed.

_________________________________________________________________________________________________________________________________

By the late 30s when the PRR realized that the aging fleet of K4s needed replacement, steam design had progressed past 4 sets of drive wheels being connected by a single side rod. The reciprocating mass of the side-rod would pound the track. The PRR instead chose to go with an articulated locomotives due to this reason (less centralized reciprocating mass), along with the fact that duplexes could use smaller cylinders, and required lower piston axial force than a conventional locomotive.

Therefore, instead of going with a 4-8-4, they went with a 4-4-4-4 (two sets of 4 drive wheels instead of one set of 8).

During the war, the government did not allow for experimental locomotive design, therefore the J1s were built from the C&O 2-10-4 design as they were needed heavier locomotives for long slow hauls (therefore no 4-8-4 freight engines for the PRR)

The S2 turbine (1944) was supposed to be a 4-8-4 design, however wartime restrictions forced the PRR to use heavier steel alloys in the locomotive (lighter alloys of steel were needed for the war effort). Therefore 6 wheel leading and trailing trucks were used.

By the late 40s, dieselization crept in and there was no need for more new steam locomotives.

Last edited by Prr7688

To follow up on Hot Water's comment, the PRR Mechanical Department suffered from more than a touch of ego when it came to locomotive design.  They were so heavily invested in trying to make the duplexes successful they initially ignored data showing the superiority of diesel power until 1947 and then ordered as many as they could find from every manufacturer as EMD couldn't provide the volume of locomotives they needed to replace what was by then a largely archaic fleet of steam locomotives.

Many suspect that if they had developed an R class steam locomotive, it would have had a long and successful career in the exact same way the duplexes didn't.

@jhz563 posted:

Since the 4-8-4 was so successful on other roads, it makes me think that the PRR must have had a specific reason no to employ the design.  It may not have even been technical.  But when you have 4-8-2, 2-10-0 and even 4-4-4-4 styles in play, it seems odd not to have this style (edited).

That seems a bit backwards. When you have a variety of alternative designs already fulfilling the role a 4-8-4 would service, I don't see what the need for a 4-8-4 would have been.

I think it has been covered, but I think there are a few reasons why PRR did not get any steam 4-8-4s (they did have at least one electric 4-8-4, class R1)

First the Pennsy from early in the 20th century had a conservative design policy that indicated that simpler was more efficient and lower maintenance.    This translated into fewer axles per loco - fewer bearings and less friction, less things to maintain.    The prime example is the E6 4-4-2 that was the equivalent to many roads 4-6-2s.   PRR had a very heavy duty mainline roadbed and track, and therefore could afford heavy axle loadings.    This design policy carried over to 2 rail trailing trucks on PRR designed stuff.    Remember the last K4s were built in 1928 which I think made them contempraries of NYC Hudsons       The M1As were built with cast steel frames and variouis other "modern" improvements at the time.

Second the electrification used a lot of available capital and made a lot of steamers excess.    An example is the many of the L1 mikados were put into storage because they were not needed and I think quite a few consolidations were sold off.    The L1s were pulled out of storage and put back in service during WWII but many did not have stokers because they had not received them prior to storage.     The M1/M1A classes could hold down the freight assignments on the Middle division and out west while the I1 decapods could handle the Pittsburgh division freight over the mountains in both directions.   PRR also looked to electrify the mainline from Harrisburg to Pittsburgh over the mountains and did at least two and I think 3 justifcation and feasibility studies.

Third by the time they were considering more modern steam in the early 40s, they realized that the bigger locos were pounding the track and causing more maintenance and making high speed harder to obtain because of the needed counter balancing.    Therefore they looked to the duplex idea (not articulated, rigid frame) to provide lighter mechanisms.     Hence the T1 and others.    The T1 could probably have been very successfull if it had been built a decade earlier.    By the time it was built, diesel electric locos had become reliable and available and there was just no need to work the bugs out of the latest steamers.

I recall in the "Thoroughbreds" book about NYC Hudsons that one of the former employees they quoted said that NYC Hudsons and Penny K4 Pacifics were both perfect engines for what they were designed to do, to run on the track each railroad had between New York and Chicago - and that they wouldn't have worked as well if you'd swapped them. Each design was unique to what the railroad that built them needed.

As far as Northerns - which were primarily heavy passenger power for top-line trains -  it seems like Pennsy had no qualms about double-heading K4s on long trains, where other roads bought larger engines so they only needed one. As noted, during the Great Depression, PRR put it's money into expanding electrification. By the time they started experimenting with 4-4-4-4 engines, the top passenger engines were diesels, like E-units...which Pennsy did buy.

Also, once the overhead was up, nation was in the middle of the various fiscal events known as the Great Depression.  Demand for services down. So it might have been cheaper overall to use what you had, even if it means doubeheading.

With the 610 test, thete were places it could not go because of clearance issues.  Could this also be a reason for no 4-8-4's?  Or did not help in the engineering of the duplex?

I think it's been hashed out enough already, but my general feeling from reading various books and magazine articles about the time period tracks with everything else here. Pennsy was extremely conservative in design, they focused on electrification, and they didn't look very far ahead into the future for alternatives. They were the Standard Railroad of the World after all, right?

When someone woke up and realized how far behind they were in the motive power department, they went for the duplex and just kept doubling down on it, tried a turbine or two, and then grabbed for diesel power of any kind. If I was a time traveling individual I would have the PRR motive department design a relatively conservative 4-8-4 in the 1934-1936 time period. Maybe 63"-70" drivers for a freight/mixed traffic version, and 80" for a passenger flyer. Or just a 70" driver version, and later advances in counterbalancing would allow it to hit higher speeds during postwar travel.

Reading about all the different modifications they made to the basic K4 makes for interesting read. Saturated to superheated, hand firing to stoker screw, and their later experiments with front end throttles, poppet valves, trailing truck boosters, and roller bearings. If they had run all their K4s locomotives through the works and added trailing truck boosters to compensate for their tall drivers and increased traffic loads, front end throttles and poppet valves for more efficient working, cast frames, and roller bearings throughout, they could have squeaked by without duplexes.

Of course my favorite PRR locomotive is the J1 which is just the C&O Texas with a Pennsy cab, so don't pay too much attention to me.

Also, once the overhead was up, nation was in the middle of the various fiscal events known as the Great Depression.  Demand for services down. So it might have been cheaper overall to use what you had, even if it means doubeheading.

With the 610 test, thete were places it could not go because of clearance issues.  Could this also be a reason for no 4-8-4's?  Or did not help in the engineering of the duplex?

Pretty sure the Penny's S1, J1's, T1's and Q1-2's were larger than any 4-8-4 the Pennsy might have designed.

Rusty

So was it that PRR had gone pro-electrification by the early 1900s for all the eastern traffic volume and Pennsylvania station? And so since they had plans to electrify further west, why develop that next gen steam (4-8-4s etc) of the mid-late 1920s?  But then the depression hit, volume and available capital must've declined putting the catenary going west on hold. Then the war, which wore out that already-tired, old steam fleet that was probabl supposed to have been replaced by GG1s and P5s (or whatever would've followed). But by this time, it became clear it was not economical to build all that electrical infrastructure when EMD had figured out how to simply put a small power plant on the electric locomotive's back. Even though I never heard about it being thought of further than Pittsburgh, the idea off GG1s stretching out to Chicago is pretty badass. Would they have had to adhere to division points, or go straight through? Could they have gotten The Broadway down to maybe, 14 hours?!

There were two articles in the PRRT&HS society's magazine, The Keystone, that gave some idea what PRR 4-8-4s may have looked like.  In Vol.31, No.1 there is a short article with specifications, and a painting of a modern PRR 4-8-4.  In Vol.33, No.3, there is another article on two PRR 4-8-4s, an early one based on the M1,  and another from the 1940s, with detailed elevations.  Still available as back issues AFAIK

So, in our little world of make-believe, why don't you create a PRR 4-8-4...you know, something like an S-2 boiler (and tender) on, say, on an ATSF class 3776 chassis?

thumbs up

Why not?

What-if's are fun in their own genre...IMHO, of course.

Imagine the workbench mayhem as you morph two fine engines into a new unique behemoth.. 

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