Thoughts on the PRR Q-2

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Thoughts on the PRR Q-2

Postby Allen Hazen » Tue Mar 15, 2011 10:54 pm

We've had some discussions suggesting that the T-1 may not have been as bad as popularly supposed; I've just been looking at something that suggests the Q-2 might also have been better than its comparatively early retirement (most out of service by 1952, all sold for scrap by 1955, at which time there were still J1 in service!) suggests.

The Q-2 was retired because of high costs. I have seen references to their fuel and water appetites, but I doubt that their consumption relative to their power was out of line: they were just big! So the main cost problem would have been maintenance. "At Columbus Shop, the Q2 cost over $30,000 to perform intermediate work that cost less than $20,000 on a J1" (quoted from book cited below). Not all that surprising: a Q-2 had twice as many cylinders as a J-1, and had a number of unusual (at least on the PRR) "hi-tech" features.

But... "The consensus of these people [I think that refers to PRR maintenance types-AH] was that if the Q2 would have significantly outperformed the J1 it might have been worth the effort, but the locomotives were so close in actual performance that it was not worth the extra cost." So: in normal use, the PRR wasn't getting any more train-pulling work out of a Q-2 than it got out of a simpler, lower-maintenance J-1. Which, given the far higher power the Q-2 attained on test is a bit surprising....

"The 50 m.p.h. general freight train speed limit effectively eliminated any horsepower advantage the Q2 had over the J1, so operating costs became the determinant." !!! The Q-2 was designed for fast-freight service: internal PRR documents when it was being designed and built refer to it as a "High Speed Freight Locomotive." Apparently, however, its superiority over the J-1 only became noticeable at... speeds higher than the PRR ran freight trains!

So, fantasy: suppose the PRR had decided to go to "mile-a-minute" freight service between Pittsburgh and Chicago. (O.k., they may have had good economic reason not to try that: I said this was a fantasy. If you want to make a plausible "alternative history" scenario, maybe you could have the containerization revolution take place a few decades earlier than in @ (that is, than in the actual world), and imagine the PRR running fleets of intermodal trains in 1949.) Perhaps in this service the higher capacity of the Q-2 would have been put to good use. In other words, maybe the early retirement of the Q-2 doesn't reflect an intrinsic inferiority of the design, but an "environmental" condition: the Q-2 was adapted to a niche that didn't, on the PRR in the WW II / Korean War period, exist.

--

Thoughs occasioned by looking at "Pennsy Q Class: classic power 5" by E.T. Harley, published by N.J. International -- I can't find a date on it, but the LC number given starts with 82, so probably within a yaear or two of 1982. Quotations are from this book, which reproduces some PRR paperwork referring to the Q-2 class as a "High Speed Freight Locomotive."

(Also posted to PRR forum.)
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Re: Thoughts on the PRR Q-2

Postby Desertdweller » Thu Mar 31, 2011 10:26 pm

Allen,

Your post suggests an unanswered question. "Why did Pennsy build a high-speed freight steam locomotive for a service that did not exist?"

Were they planning to impliment the service when the machines went into production, then later changed their mind? Or did Diesel locomotives make the whole high-speed steam concept obsolete?

A contemporary Western railroad comparable to PRR (UP) embraced the concept of high-speed steam freight and ordered locomotives comparable to the Q-2 for that service. And used them successfully. What made the 4-6-6-4's and 4-8-8-4's successful on the UP, when the Q-2's were unsuccessful on the PRR?

Both roads had equal access to Diesel locomotives and the money to spend on them. Both roads had mountain grades to contend with. Both roads were known for their innovative motive power designs, and the willingness to experiment.

Why didn't Pennsy go with Challengers? They were a proven design on several railroads for high speed freight service.

UP tried a whole gamit of turbine locomotives (steam turbine electric; gas turbine electric; powdered coal turbine electric) and practically every road freight Diesel design sold in this country before finally dropping the fires on their steamers.

I've posed a lot of questions here and answered none. But I suspect the answer to the Q-2 question lies in the answers to these questions.

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Re: Thoughts on the PRR Q-2

Postby Allen Hazen » Sat Apr 02, 2011 12:34 am

Desertdweller--
The things I was reading -- E.T. Harley's book was the main one -- when I posted the first item on this string suggest answers to a couple of questions.
"Why not a Challenger?" (It would have been a GG-5 in the PRR locomotive classification system!) Before they started building the J-1 Texas (to, basically, a decade-old C&O design) they tested A Norfolk & Western A-class 2-6-6-4, and decided in favor of the C&O design. Possibly the wrong decision, after the wrong test: they apparently tested it on the Altoona hill, whereas N&W used the A-class on moderately graded lines. In any event, the PRR apparently wasn't impressed by it, and decided to go with rigid-frame design.
"Why a high-speed freight design at all?" Well, "high" is relative! On main lines in the Western half of the system, the PRR wanted a 50 m.p.h. freighter. When the J-1 was new it apparently had dynamic augment problems (pounding the rails), and the PRR thought something with lighter cylinders and rods and lower maximum piston forces would be better even at that speed: hence the designs for the Q classes. Ironically, the J-1's problems turned out to be solvable -- annoyingly, I couldn't find details on the fix, but I suppose it might have involved a small change to the driver counterbalance weights -- with the result that it gave perfectly adequate service at 50 m.p.h.
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Re: Thoughts on the PRR Q-2

Postby mp15ac » Sat Apr 02, 2011 9:11 am

What I recall reading about the J1's was that Pennsy got the original 1930 specs on the C&O T-1's instead of the 1940 specs, which had the corrected values for the counterweights. So Pennsy had to do what C&O did ten years earlier.

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Re: Thoughts on the PRR Q-2

Postby jgallaway81 » Sat Apr 02, 2011 12:43 pm

This is a duplex answer to the duplex issue on the PRR.

As I recall, alot of the thinking behind the duplexes was the idea of solving much of the dynamic augment problems by reducing the rotating masses... breaking a 4-8-4 into a 4-4-4-4 duplex, and the 2-10-4 into the 4-6-4-4 & 4-4-6-4 engines. (My belief on the use of the 4-wheel lead truck is that Pennsy wasn't happy with the tracking ability of the 2-wheel at speed.)

A side benefit to this was that by reducing the need for huge siderods to provide integrity under the giant forces from the pistons, the engines could then use that power for pulling a train.

It seems to me that PRR was trying to build a rigid frame articulated... in that they wanted the structural integrity of the rigid frame with the running characteristics of an artic with lighter reciprocating masses. Granted, this is half-century,keyboard railroading.

Its a real shame that the C&O didn't go looking for T1 replacements a few years earlier... if they had, we might have had a chance to see the C&O H8 2-6-6-6 go head to head with the N&W A 2-6-6-4 on the Allegheny grades. Wonder which PRR would have chosen then... 2-10-4 or 2-6-6-6. Keep in mind, the Allegheny was underutilized by the C&O... lower boiler pressure & smaller pistons than designed, and no booster installed.
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Re: Thoughts on the PRR Q-2

Postby Desertdweller » Sun Apr 03, 2011 11:03 pm

Actually, the UP tried the "rigid-frame articulated" (now, there's an oxymoron!). The 2-12-4 was essentially a rigid-frame Challenger. It was 3/4 of a Challenger in cylinders, too, with a center third cylinder. Maybe PRR should have evaluated one of these.

Using the old set of specs for the C&O T1 clone was just a case of sloppy research.

Using a duplex drive in an effort to eliminate a pair of siderods seems to me like an extreme solution with little gain.

If it was 1940, maybe they would have been better off trying FT's.
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Re: Thoughts on the PRR Q-2

Postby jgallaway81 » Mon Apr 04, 2011 1:29 am

Desertdweller wrote:Actually, the UP tried the "rigid-frame articulated" (now, there's an oxymoron!). The 2-12-4 was essentially a rigid-frame Challenger. It was 3/4 of a Challenger in cylinders, too, with a center third cylinder. Maybe PRR should have evaluated one of these.

Using the old set of specs for the C&O T1 clone was just a case of sloppy research.


Okay, now you WILL have to explain this one. What exactly do you consider sloppy research? Obeying federal law in a time of war?

Using a duplex drive in an effort to eliminate a pair of siderods seems to me like an extreme solution with little gain.

If it was 1940, maybe they would have been better off trying FT's.

It wasn't about reducing the NUMBER of the rods, it was about reducing the WEIGHT. The rods for the two x-4-x driver sets weighs less than the equivalent set for a x-8-x. This is because the rods don't have to survive the same amount of thrust from the pistons, so they can be made less bulky.

Please explain your statements.
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Re: Thoughts on the PRR Q-2

Postby Desertdweller » Mon Apr 04, 2011 2:26 pm

JG,

Ok, fair enough.

My reference to "sloppy research" was in regards to mp15's post. The C&O had devised a set of specs for their T1 in 1930. This set of specs was revised in 1940 to alter counterweights in order to reduce dynamic augment. If the Pennsy based their locomotive on the T1 design, it would have been due diligence on their part to research the values in use on these engines at the time. Failure to confirm the optimal specs in use ten years after the original design sounds to me like sloppy research.

What do you mean by "obeying Federal law in a time of war"? The US was not at war in 1940. The only concievable way Federal law could have been broken in this instance would be if the weight of the counterweights on the C&O engines were a proprietary trade secret, or protected by US patent. Since the entire locomotive design was lifted from the C&O, I don't see how a patent infringement could have occured.

As to your second point, the only increase in siderod weight would be the length of the rod needed to connect the two sets of drivers. Yes, that would be additional rotating mass. At the cost of eliminating that weight, the Q-2 required a second set of cylinders and valve gear, a second set of piston rods (which are reciprocating weight, and probably as heavy as the addition length of siderod would be), and the piping needed to route steam to and from the second set of cylinders.

An extreme solution for questionable gain.

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Re: Thoughts on the PRR Q-2

Postby jgallaway81 » Tue Apr 05, 2011 1:55 am

Desertdweller wrote:JG,

What do you mean by "obeying Federal law in a time of war"? The US was not at war in 1940. The only concievable way Federal law could have been broken in this instance would be if the weight of the counterweights on the C&O engines were a proprietary trade secret, or protected by US patent. Since the entire locomotive design was lifted from the C&O, I don't see how a patent infringement could have occured.


Lifted from wikipedia: The PRR J1 was a class of 2-10-4 or "Texas" type steam locomotives with 69 in (180 cm) driving wheels built between 1943 and 1944. The J1 had over 95,000 pounds-force (422.6 kN) of tractive effort, plus an additional 15,000 lbf (66.7 kN) if the booster engine was used.

This means, that YES, the United States was at war, and in fact it was federally mandated that ALL steam engines built MUST be of existing, working, acceptable designs. This is why the J's don't have belpaire fireboxes, because the government wouldn't allow them to modify the design.

As to your second point, the only increase in siderod weight would be the length of the rod needed to connect the two sets of drivers. Yes, that would be additional rotating mass. At the cost of eliminating that weight, the Q-2 required a second set of cylinders and valve gear, a second set of piston rods (which are reciprocating weight, and probably as heavy as the addition length of siderod would be), and the piping needed to route steam to and from the second set of cylinders.

An extreme solution for questionable gain.

Les


Okay, theory: double the cylinders makes piston thrusts half. half the forces encountered means structure needs less bulk to maintain integrity.

IE: If a 4-8-4 produces 90,000 of piston thrust, then a duplex of the 4-4-4-4 arrangement should have 45,000pounds thrust, while producing the same available train power. Since the piston thrust is less, ALL the drive rods can be less massive since they need to carry less force. Since the rods are lighter, the counterbalance is less massive, more of the piston thrust goes to train pulling than moving the reciprocating mass. This then means that the piston thrust could be reduced even more to produce teh same amount of pulling effort.

I'll admit the numbers are likely off, but it exemplifies the theory.

Now, was the theory correct as applied? That I don't know, and short of getting out the PRR test data, I know of no way to confirm other than to build two new engines and actually test them... course, computers could probably have the answer in fifteen seconds.
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Re: Thoughts on the PRR Q-2

Postby slide rules » Tue Apr 05, 2011 7:04 pm

Hi all,

J. D. Gallaway is essentially correct in his assessment of the theories behind duplex drives. I recall that dynamic augment was a big target of the duplex drive camp, that is to say REDUCING dynamic augment, and that has to do with rods. More specifically, if you think about it, one end of the rod moves in a circle, one end back and forth in a horizontal plane. These forces cannot all be balanced with wheel weights, which of course also move in a circle, although the practice of "cross counterbalancing" did help greatly.

Piston thrust problems had been around for some time, and large engines like 2-10-2's required massive, heavy frames to handle the forces. Also, larger diameter axles were needed, and in most cases 62 or 63 inch wheels couldn't begin to offer enough space for adequate weights for counterbalance, unless a very very low top speed were to have been imposed to keep rail hammer down. 4-8-4's had also began to creep up in piston thrusts, as boilers got up to 275-300psi. Even with large drivers, counterbalance was a problem, but so were frames. The duplex drive also offered the possibility of smaller cross section frames, which could save weight. Yes, it made for a longer locomotive, but having that torque divided into two separate cylinder saddles was a big difference.

Another thing with duplex drive that isn't often mentioned was the possibility of better proportions of steam and exhaust passages. Arguably the boiler of two locomotives, one duplex drive and one not, but of the same total wheel arrangement, would be about the same size, and was, within reason. Having two sets of cylinders actually improves the ratios of supply pipe and exhaust pipe to cylinder volume ratios, not to mention that valves can be proportionally larger, which also greatly aids power. Just look at some of the power figures developed by duplex drive locos to see this proven.

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Re: Thoughts on the PRR Q-2

Postby Allen Hazen » Tue Apr 05, 2011 9:37 pm

Dave Davis--
Thanks for lucid explanation!
I hadn't thought about the frame issue before. (My understanding is that one way of minimizing dynamic augment was to change the counterweights so that LESS of the fore-and-aft component was balanced: that locomotives like the New York Central's Hudsons and Niagaras had counterbalancing that came close to perfect balance of the rotating mass, so the vertical component of "hammerblow" was minimzed, at the expense of NOT doing as much to counteract the fore-and-aft forces. And that this was made possible by the use of very robust -- one-piece cast -- frames. So -- I would assume -- frame weights grew enormously in the late steam era.)

Do you know if the PRR took advantage of the duplex arrangement to reduce frame weight? I think all Q-2 were built with one-piece frame castings (I think this was pretty much standard practice late in the steam era, and that the only reason why some of the J-1 were NOT built with one-piece beds was probably unavailability in wartime(*)). Were the Q2 frames lighter or smaller in cross-section than the J-1 frames (on those J-1 that had cast frames)?

Not that weight reduction seems to have been high on the agenda for PRR's steam designers! The Q-2 was a VERY heavy locomotive, with very high per-axle weights on the drivers...

(*) I think I've had the difference between a J-1 and a J-1a explained to me, but I don't remember it. It WASN'T one-piece versus constructed underrframes: some of each subclass had each frame type.
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Re: Thoughts on the PRR Q-2

Postby Allen Hazen » Tue Apr 05, 2011 9:45 pm

MP15ac--
The PRR built the J-1 to the ORIGINAL T-1 design, not incorporating the improvements that C&O had figured out over the course of a decade?
That is MIND-BOGGLING! (I'm not expressing scepticism there, just amazement!)
It would explain why the J-1, when new, had problems, and also why they were largely cured by the time the Q-2 was introduced. Railroad mechanical officers from different companies met regularly at conferences. Do you suppose that, at some get-together in about 1945, a PRR man said to his C&O opposite number "How do you live with the track-destroying hammer-blow from those Texas types?" and that his jaw dropped when the C&O man replied "Oh, we solved that problem years ago-- didn't you people get our revised spec on wheel balance weights?"
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Re: Thoughts on the PRR Q-2

Postby jgallaway81 » Wed Apr 06, 2011 7:04 am

Another thought is that perhaps PRR had different standards from which they judged WAS excessive hammer-effect.

C&O may have accepted 15,000pounds of effect while PRR wanted only 8,000pounds. I have no idea if this is a valid theory, but without numbers from each, its just as valid as any other theory put out.
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Re: Thoughts on the PRR Q-2

Postby Desertdweller » Sat Apr 09, 2011 9:02 pm

jg,

I really do not follow your point on the Federal ban on building new designs, if the J was essentially a T-1. Would a modification of counterweights really be considered a new design?

As far as dynamic augmentation goes, doesn't reciprocating mass pound rail more than rotating mass?

I'm a locomotive engineer, not a mechanical engineer.

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Re: Thoughts on the PRR Q-2

Postby Allen Hazen » Sat Apr 09, 2011 9:59 pm

Desertdweller--
re first query: Gov't rules (War Production Board) prevented any MAJOR innovation (and I have seen it said that changing the round-top boiler design of the T-1 to a Belpaire-- which might, a priori, have been the sort of thing the PRR would have liked to do-- would have counted as a "new design" and so been verboten). Minor changes were allowed, and in fact the PRRT J-1 is not an exact copy of the C&O T-1: the PRR used larger driving wheels (by 1" in diameter) and a higher boiler pressure (by 5 or 10 lbs/sq in). So it seems clear that IF the C&O had recised the counterweights, the PRR would have been ALLOWED to use the recised specs. Which makes it all the more remarkable if they didn't!

re second: I'm not a mechanical engineer either, so this is an amateur's guess-work. "Hammer blow" (dynamic augment) is described in terms of the additional force directed downward onto the rail (described, in other words, as if the weight on the axle was momentarily increased). As a matter of physics, I would think that this effect would be produced by moving weights up and down: so, by the rotating masses of the rods. If this were all that you had to worry about, you could add counterweights that exactly balanced this. (The PRR S-2 steam turbine locomotive is described as having "perfectly" balanced drivers.) The complication, as I understand it (if I'm wrong, somebody please set me right!) is that the reciprocating masses have OTHER undesirable effects (they "try" to induce a yawing motion in the locomotive, which bends the frames back and forth with each piston stroke), and to counteract these weights were added to the driving wheel conterbalances... with the end result that they WEREN'T perfectly balanced as regards rotating mass. (But-- once again-- I don't fully understand the details here.)
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