In terms of steam locomotives that were assigned to commuter services and required good acceleration capability, which designs worked best?
Well, the classic answer to this is the "Decapod" 0-10-0 custom-designed for suburban London service (instead of MU electrification). All wheels driven, good steam reserve, no need for sustained high speed -- on the whole, an interesting design optimized in interesting and somewhat unexpected ways.
Other aspects of commuter design, such as bidirectionality and the use of fuel and water weight for adhesion, indicated that a tank locomotive was a preferred configuration for runs short enough. A suitable example might be the M7 class that Bulleid's "Leader" was (supposedly!) intended to replace.
Precise valve gear could be an advantage, as could the inherent negative starting lead of Stephenson gear. Good water rate could be an advantage, but most services wouldn't 'pay' for expensive thermodynamic 'enhancements' like pumped feedwater heaters. Note that either too high or too low a driver diameter would compromise overall efficiency -- looking at the size a given railroad used in a given service for any length of time is probably a reasonable guide.
Ulrich,
Unlike the automotive internal combustion engine the steam locomotive existed in an age of history characterized in technology by the term Industrial Arts. This means that "science" as we would understand it today did not necessarily exist in the same terms. There were no computers to accomplish advanced mathamatical engineering calculations and no cad-cam electronic design facility that would allow three dimensional cyber engineering projections. Drafting Paper and pen were the advanced design tools.
Railroad steam locomotives as such were therefore designed by expertise on the part of the design engineers and their design was worked out over time and with experience in the "school of hard knocks." Yes, there were experts and "guru" talents like Paul Keifer of the New York Central who came up with uniquely workable engines, but on the whole, few paramaters existed that would define a particular set of standards that would produce a true "high performance" design.
Some railroad engines did, however, become famous for their unique ability to perform at speed and in acceleration with passenger work. Other engines owing to their overwhelming size and inherent power accomplished the same goal.
Possibly the Pennsylvania Railroad with its massive investment in "Duplex" engines with equally massive investment in diagnostic test facilities could lay claim to the title - the advent of a "Railroad Scientific Age."
Pennsy had the Altoona Test Plant with its stationary power test dyanometer and also the money and design department to develop the 6-4-4-6 the 4-4-4-4, the 6-8-6 turbine, the 4-6-4-4 and the 4-4-6-4.
Pennsy also did extensive work in the developing field of "poppet valve" design and utilization of "low cutoff" expansive steam usage, an area that really demanded future development. No records exist, however, as to whither the 4-4-4-4 duplex designs featuring "low cutoff" were engines of outstanding acceleration as well as top speed.
Even the locomotive manufacturers ALCO, BALDWIN and LIMA did not have test facilities like the Pennsylvania Railroad. Further none of the manufacturers ever did any performance testing of locomotive designs for themselves. All of this was left to operating railroads. Truely the railroad steam locomotive of the time existed in an age of Industrial Arts.
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This brings us to the subject of "Practical Engineering" where rare occurances of recorded steam locomotive performance are documented. One of the few records I have ever seen on steam locomotive acceleration is included in Alvin Staufers book Thoroughbreds recounting the uniquely successful history of the New York Central J3 "Hudson" 4-6-4 passenger engine.
Here in Michigan, famed for automotive production, an engine crew took upon themselves to go about testing the performance of the NYC J3 "Hudson" in practical operation.
Here is their surviving report.
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Raymond K. Smith fireman for NYC writing from Lansing, MI -
"I had the pleasure of firing one of these engines in a branch line passenger run in 1955 on trains 351 and 352."
"Our regular engine was J3 5429. It was a pure delight to fire this engine. While we had rather light trains, seven to eight coaches, there were places that we could test the true performance of the engine. One such place was Owosso, Mich. where southbound trains climbed a steady grade for about three miles out of town. We planned to test the time from stand still to sixty using standard stop watch."
"I allowed the water to just show in the glass and prepared a hand fire while doing station work."
"When we recieved the highball, the engineer, H. Brazee, started the watch and opened the throttle. The engine slipped once but otherwise worked at full power. In exactly 90 seconds the speed recorder crossed sixty, the track speed. It was interesting to note that on an L4 (NYC Mohawk 4-8-2 passenger engine) in good running condition with the same train required 2 minutes to obtain the same speed."
"Later, with steam-power retired, we tried this test with a single General Motors GP-7 (diesel electric) Passenger engine. Unfortunately we never completed the test as the engine never reached 60 mph until we passed the next town."
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So many variables went into steam locomotive performance that unless you had an engine crew specifically capable of doing a test such as this - these performance paramaters of acceleration were seldom if ever tested.
Notice that the crew prepared a hand fire - also that the water level in the boiler was allowed to be "low in the water glass" - a particular trick that really let the engine perform, and pushed the boiler to its thermal limit - little tricks of the knowledgable engine crew.
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Chesapeake and Ohio Railroad also did numerous engine tests using a full engineering staff with trains pulling a company dynometer car - testing for engine power, fuel consumption, loading etc. but not necessarily for acceleration. As did many other railroads also. No one I ever read was particularly concerned with steam locomotive acceleration in the modern engineering sense.
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Hope this helps answer your question -
Doc
Doc, didn't he restrict his original question to commuter work -- where repeated high acceleration is critical to producing good service?
Both PRR and NYC understood the appropriate use of acceleration in a number of respects. From the traces on a PRR TE vs. speed chart, you can easily extract a curve for acceleration at any given train resistance or factor, for example. PRR in fact was so sensible that they had a nomenclatural difference between helper locomotives (which got greater weight up a grade) and snappers (which got a train up the grade at higher speed or a shorter time). NYC of course invented the trailing-truck booster in part to give faster acceleration without driver slip under a given set of adhesion conditions.
Naturally there was usually more 'emphasis' on passenger-train handling than freight, even what passed for 'fast freight' on most railroads, and passenger trains have more of a 'vanity cushion' of available horsepower at slow to medium speeds -- all too often even in the post-drag era the temptation was to 'add loads right up to the ruling-grade capacity of the engine'.
To see an example of science and mathematics involving acceleration of steam locomotives, I need look no farther than a page I left open from a reference search on automatic cutoff control (p.326 of the September 10th, 1921 Railway Review) and then follow to the other references cited there. There is also Lawrence Fry's analysis from 1923 (which I personally find of low practical value because of all the empirical constants and assumptions that don't match modern designs) and his analysis of locomotive test-plant operation from 1925. Just because rapid acceleration wasn't always a design priority didn't mean engineers didn't understand how to optimize it, or understand what its analysis involved -- in a sense, any approach that optimizes drawbar pull every couple of mph between speeds will also optimize the rate of acceleration.
Look at some of the discussions of the C1a vs. 'production' T1s for some better understanding. Precise short cutoff was not something that would enhance either low-speed acceleration or limits on slipping. Meanwhile, both these designs were as short-stroke as driver construction permitted, likewise a formula for slow-speed problems. Most of the surviving material indicates T1s were slow to accelerate up to about 35mph, at which point they started accelerating more strongly than anything in the competition. It's at very high speed that the advantages of precise cutoff begin to show themselves (both in power and improved water rate) but at the same time the precise and higher peak effective pressure may lead to high-speed slipping that propagates for more than a revolution each time an unconjugated engine loses adhesion on one or more drivers.
There are more important high-speed considerations, too: one is effective bypass to avoid 'engine braking' if the power needs to be reduced quickly -- it is NOT a good idea to do strong 'dynamic braking' using the driver tires! -- and another is prompt and effective compression control (ideally reversible, but that hasn't to my knowledge been tried on locomotives directly).
Could you be thinking of the Lima "long compression" that was a feature of Franklin "type C" poppet gear (never, perhaps unfortunately, applied to an actual high-speed locomotive)? That most certainly would have had an effect on low-speed performance, among other things making the theoretical 2-5% cutoff of something like British Caprotti physically usable. But that again is more something giving smoothness over the length of the stroke, and reducing the heat and water rate, than something giving higher acceleration for a given engine size, I think.
RME Could you be thinking of the Lima "long compression" that was a feature of Franklin "type C" poppet gear (never, perhaps unfortunately, applied to an actual high-speed locomotive)? That most certainly would have had an effect on low-speed performance, among other things making the theoretical 2-5% cutoff of something like British Caprotti physically usable. But that again is more something giving smoothness over the length of the stroke, and reducing the heat and water rate, than something giving higher acceleration for a given engine size, I think.
2-5% cutoff? The indicated efficiency might be great, but even leaving aside cylinder wall condensation and piston friction losses, would you extract any usable amount of HP under those conditions, even if only to maintain "cruising speed" in a lightweight, streamlined express passenger train? That is, as if there were such a thing as a low-power "cruise mode", even on a lightweight train, given the up and down grades on an even a nominally flat stretch of track?
That is one of the concerns regarding direct-drive reciprocating steam. Peak efficiency may be at short cutoff and hence a low part load, well below where you get useful work from the locomotive?
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul Milenkovic2-5% cutoff? The indicated efficiency might be great, but even leaving aside cylinder wall condensation and piston friction losses, would you extract any usable amount of HP under those conditions, even if only to maintain "cruising speed" in a lightweight, streamlined express passenger train?
Give that man a gold star -- he saw the right question (not surprisingly, to me). In fact, discussions of British Caprotti sometimes raise exactly this issue: that at some point higher speed requires longer, not shorter, cutoff (Mallard was up to somewhere right at 40% at 125mph indicated) so the ability of the gear to command very short admission time is something of a mechanical curiosity rather than a performance/economy advantage.
On the other hand, the precision setting allows timing, phasing, and duration all to be customized within that general percentage 'error' rate. I don't know of it actually being adjusted or utilized that way, but it certainly could be, with a number of devices used to optimize the physical settings moment-by-moment if desired.
Remember that in the long-compression setup, the idea is to admit a reasonable mass-flow of steam within a precise admission window, with subsequent expansion to get the most thrust out of the steam (and high enough superheat that nucleate condensation doesn't cripple the effective pressure producing that thrust while there is still nominally-usable enthalpy in much of the surrounding steam).
Wall condensation is another set of issues, which in my opinion involves both preheat ("jacketing" being one version, although how I propose to do it is very different from just piping exhaust steam around) and careful materials/tribology use. I do think there are situations, for example high-speed drifting without admitting air or excess steam for snifting or producing the wrong kinds of 'vacuum', where very short and precise cutoff settings would have utility, but I would almost immediately note that there are better approaches for many of them which don't require nightmare-box complications or excess precision.
Peak efficiency may be at short cutoff and hence a low part load, well below where you get useful work from the locomotive?
In my opinion, the situation (at least with modern fairly large locomotives of the type I'm interested in) is more complicated. For example, in some UP FEF testing it was quite possible for the locomotive to make adequate cylinder power without having enough draft action to sustain steam generation even at 'optimized' cutoff for running. Tuplin found that 'peak efficiency' for a Niagara (in terms of minimizing both fuel and water consumption for the work of a way freight normally handled by something, say, 2-8-0 sized) could be right at 2-8-0 levels, even in that large firebox, in part by using sliding-pressure firing down to his beloved 160psi or below range. On the other hand, it's very clear from the PRR T1 testing that optimal water rate came at a fairly high horsepower output but not the highest range of road speed. It was my understanding, perhaps wrong, that one of the most important 'empirical' aspects of locomotive design was to optimize "peak efficiency" around the anticipated mission of a locomotive, while preserving automatic action for lower speeds, the ability for 'dash capability' if that were necessary, etc.
Ulrich In terms of steam locomotives that were assigned to commuter services and required good acceleration capability, which designs worked best?
Could the popularity of different engine types be an indication of which types worked best? In commuter service, the PRR, and especially their LIRR subsidiary, seemed to favor the modern 4-6-0. Many RRs used 4-6-2's, but I woner if that was because of availability of locos bumped down by more modern steam or diesels. Speaking of tank engines, CP used the 4-6-4T in commuter service.
Consider that the G-5s was designed primarily for Pittsburgh commuter service and was found to be useful elsewhere. PRR also seemed to have an aversion for trailing trucks in its design practices, what else explains the I-1 when most roads would use 2-10-2's in similar service.
Your question implies that railroads designed engines for commuter service, which in the vast majority of cases was not true. By far the most common engine was the previous generation's main line passenger power in the usual progression of 4-4-0, 4-6-0, and 4-6-2.
Most successful would likely have been relatively small driver diameter, say 63", with good factor of adhesion (4 or over). No need for high speed, or sustained running, so big drivers, huge fireboxes, and four wheel trailing trucks were unnecessary, and in fact extra cost handicaps.
Somone mentioned tank engines. Southern Pacific had three 2-4-2T built in 1883 and 1889, one with 54 and two with 48" drivers. Sacramento built seven 2-6-2T engines with 48" drivers in 1881 and 1882. The 48" drivers were evidently a bit to small as in 1894 they got 51". These are exceptions that prove the rule of using last generation road engines since SP operated steam commuter trains for decades with many other engines.
Accepting that the G-5 was designed for commuter service, and who but the PRR would have the need and money to do so, it seems to prove the desriable features. Since I am not a PRR fan I do not have specs but would suggest check driver size and factor of adhesion. The reason not to hang a trailing truck on the design is to keep the weight where it will do good, that is on the drivers.
Mac
What, no mention of the Boston & Albany 4-6-6T?
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BigJim What, no mention of the Boston & Albany 4-6-6T?
That is correct.
Ulrich,You might find something interesting here:http://cs.trains.com/ctr/f/3/t/244713.aspx
I recall a Trains article on the Pennsy G-5s, which also ran in the commuter service Chicago to Valpo.
C&NW, CA&E, MILW, CGW and IC fan
Previous posts about engineer getting arm broken by unwanted movement of reverser is interesting. The PBS series of Victoria showed what apppears to be a replica of a very early steam loco. There were 2 levers on left side that continously moved when loco was moving. Talk about a hazard. Any of our UK posters know more ?
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