You are correct about minimum speed, and the electronc controls prevent field coils from receiving higher current than their insulation can handle because of heat, so ammeters are not necessary. What might be meant by minimum speed would be related to a particular grade and the experience of the crew of knowing that when speed drops below a certain value a stall is likely to occur. But the stall will not damage the locomotive, and you are correct.
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rgbpainterWhat a marvelous insight. It might be important in passenger service if you're trying to make up time. It would be less important in freight service where schedule is important to be sure, but not as important as in passenger service.
A couple more insights for you: High horsepower becomes valuable two places in passenger service: in some commuter service, where high repeated accelerations are needed for even mediocre timekeeping, and in very high speed service (for example, what the Niagaras did on NYC). High horsepower becomes important for freight service when there are relatively frequent stoppages, especially of the 'new' longer trains, e.g. when there is a repeated need to take siding or re-crew. Here repeated accelerations are not related to higher speed or shorter timing, but simply because the train must be stopped and then restarted more often.
Actually, there is no minimum continuous speed for an AC motor locomotive. AC motors have none of the detrimental heating effects that are associated with DC motors. An AC locomotive doesn't even have an ammeter to record short time ratings. An AC locomotive can stand still at full throttle registering 200,000 lbs of tractive effort with no adverse affects. It is not a normal operation, but it has been demonstrated on several occasions.
"Horsepower becomes important with acceleration ..."
What a marvelous insight. It might be important in passenger service if you're trying to make up time. It would be less important in freight service where schedule is important to be sure, but not as important as in passenger service.
But that's just this old non-railfan talking. I live for insights, not details.
All this is true, but much less true with AC traction motors than DC. For equivalent HP and gearing AC's minium continuous speed at full throttle is about 1/3 that of DC.
He's right, of course. I was thinking in terms of 'transition'era' power like FTs or MUed early Geeps that had a large number of traction motors for the available horsepower, but even then there were limitations on wheelslip and short-term motor rating that would limit application of the available main=generator power 'to the rail'.
One of the reasons TE was used in determining steam-locomotive capability is that reciprocating steam locomotives can develop a substantial percentage of rated TE at very low or zero rpm, which diesels with DC traction motors cannot safely do for long.
WizlishDiesels are concerned with horsepower because they can 'start any train they can pull'
Then why do we have slugs?
It has long been my understanding that diesels don't have the adhesion to take maximum advantage of their capabilities at slow speed. The solution are slugs to allow an engine to essentially do the work of two at slow speeds where it otherwise wouldn't be able to take full advantage of its power output due to wheelslip, by allowing a higher throttle setting and splitting that power between an extra set of traction motors.
Diesels can't start every thing that they can pull. Slugs wouldn't exist if that wasn't the case. But with a slug, a GP40 with 3,000 HP for instance can essentially do the work of a pair of GP38's at slower speeds despite being down 1,000 HP.
Horsepower becomes important with acceleration and track speed. Something like a GP60 produces too much power at slow speeds for it to take full advantage of it. Everything otherwise equal, the benefits of that extra horsepower over something with perhaps half the hp isn't in how heavy of a train that it can get rolling, but in its ability to continue accelerating that load to a higher speed past where the weaker locomotive would've topped out.
sgriggs tomikawaTT When steam was king the road foremen of engines were concerned with tractive effort and tonnage rating. Horsepower? Who cared? Implied in that tonnage rating was time over the road, which was a function of horsepower. If railroads didn't care about horsepower, they would have all stayed with low-drivered drag designs from the USRA era. Some did, to be sure, but most of the big railroads developed high horsepower designs with large grate areas and drivers larger than 65".
tomikawaTT When steam was king the road foremen of engines were concerned with tractive effort and tonnage rating. Horsepower? Who cared?
When steam was king the road foremen of engines were concerned with tractive effort and tonnage rating. Horsepower? Who cared?
Implied in that tonnage rating was time over the road, which was a function of horsepower. If railroads didn't care about horsepower, they would have all stayed with low-drivered drag designs from the USRA era. Some did, to be sure, but most of the big railroads developed high horsepower designs with large grate areas and drivers larger than 65".
Yes, but... What he's saying is that a RFE isn't concerned with a number for 'locomotive horsepower' (which would be largely useless for his practical purposes, for example if the HP rating corresponded to a speed and conditions which the locomotive could not reach with a rated tonnage train over critical portions of its route, or if a nominally high-horsepower engine might become 'stuck' or require expensive doubling or helpers even on occasion). The situation might be analogous to the Kodak 'guide number' system, where an arbitrary number derived from a weighted calculation involving multiple technical inputs is a more reliable guide to overall 'performance' than just one of the inputs would be. Compare the use of 'car factor' in determining the opposite requirement, effective train resistance (instead of 'tonnage') as a determinant of the most profitable train a given locomotive will pull.
Diesels are concerned with horsepower because they can 'start any train they can pull' and that performance is explicitly horsepower-limited over a wide range of speed. Steam performance, and practical limits on it, are different and not as clearly definable.
I thoroughly agree that a better recognition of steam horsepower and the conditions under which it is generated might be made in determining tonnage ratings for particular services. One interesting example (albeit not made to optimize either average road speed or minimized 'turn' time per se) is the N&W maximization of efficiency over the bridge at Kenova that led to the adoption of A-tanks, as Ed King described. A counterexample was the alleged misuse of the Allegheny locomotives by working them consistently on services with frequent slower speeds that would not permit maximum HP development or concomitant efficiency from those locomotives.
The catch is that the 'business' of railroading does not often involve running motive power most efficiently; it concerns the movement of freight with the best profitability. For various reasons the 'short, fast train' model, even though promoted by a head as wise as Perlman's, has only caught on in relatively restricted markets for essentially restricted times. We now find ourselves in an era where 40 mph road speed is becoming the 'new one-speed railroad' metric, tonnage expands to fill the power allotted to it, and -- perhaps enlighteningly if we know where to look -- maximum horsepower per unit only rises above 4400-4500 HP with great difficulty, and so far only in special circumstances evidently not generally observed in the general market for (expensive) locomotives.
As an aside -- there are decidedly similar considerations regarding high-horsepower locomotive designs, even ones like the NYC Niagara that could be almost preternaturally efficient at lower output when operated that way. The Niagaras were all put out of service relatively long before the end of steam on NYC, and it can be instructive to consider the reasons why ... both the legitimate ones and the excuses.
As an aside: many (perhaps most) of the PRR locomotive-comparison graphs used 'tractive effort at speed' and not horsepower per se. I have seen Santa Fe measurements expressed the same way. Granted you need two discrete pieces of data for a given reading, but one of them is directly usable for determining tonnage at the point the other is observed or desired. 'Horsepower' defines the situation in a different way (with pure time as one of the variables).
tomikawaTT When steam was king the road foremen of engines were concerned with tractive effort and tonnage rating. Horsepower? Who cared? Chuck
Chuck
I would say about 2800-3000 DBHP at around 30mph for a standard 2-10-2 with 63" drivers.
CSSHEGEWISCH Electric locomotive horsepower is a lot more variable since it draws its power from an outside source. Continuous hp is the most common figure, which is the amount that can be produced all day without damaging the equipment. Short-term ratings can be higher, limited by the time allowed before the extra heat generated will damage the electrical gear.
Electric locomotive horsepower is a lot more variable since it draws its power from an outside source. Continuous hp is the most common figure, which is the amount that can be produced all day without damaging the equipment. Short-term ratings can be higher, limited by the time allowed before the extra heat generated will damage the electrical gear.
Likewise, conventional steam locomotives have the equivalent of 'short term' ratings. There is a large store of energy in the supercritical boiler water (think of how a 'fireless cooker' works) which can be drawn upon to produce more power from the cylinders (up to close to the indicated hp at any given cutoff) regardless of what the firing can sustain.
Note that most of the 'horsepower' formulae developed by locomotive builders involved a conservative pressure rating (at say 85% of nominal boiler pressure). The locomotive could naturally develop more power at the times the boiler pressure was actually higher than the level used for the calculation.
You can easily determine the horsepower of a diesel. Just look at the data plate on the engine block.
You can determine electric locomotive horsepower by multiplying the data for one traction motor by the number of traction motors.
Steam locomotive horsepower is a curve - zero standing still, rising to some maximum at the 'sweet spot' where steam production exactly equals steam consumption at the bolier's maximum output, then falling as cutoff has to go beyond optimum to allow increasing speed. Note that the 'sweet spot' would vary with trail tonnage and track conditions, and that very few drag freight engines ever approached it in operation. The only way to make a credible (not mathematically modeled) determination was to couple a dynamometer car behind the tender - which was NOT done for every run.
Hello good Sir!
You can't find the horsepower values because none were probably ever recorded. USRA designs were built in the drag-freight era, IIRC. During that time the usual practice was to pull as much tonnage as possible, accepting the low speed. This means that there wasn't as much need for high steam production... Which means that the locos couldn't be run very succesfully on faster freight trains, usually working coal trains or comparable until the end of their working life.(All of this might be wrong and I can't qoute any source for it... Sorry)
Anyway, here's a handy little site to compute TE and Power, it's for a train simulator, but can be used perfectly well without any:
http://www.coalstonewcastle.com.au/physics/steam-set/
Click on the boiler parameter calculator if you're interested in making your own computations.
For now, here's a little list of power outputs and speeds:
Light 2-10-2:2780ihp at 32mph.
Heavy 2-10-2:3280ihp at 35mph.
Light 2-8-2:2580ihp at 37mph.
Heavy 2-8-2:2650ihp at 35mph.
Light 4-6-2:2390ihp at 47mph.
These numbers are probably too optimistic for drag freighters (well, for anything but the Light 4-6-2, which was obviously an express-loco), I'd assume that they'd run out of boiler pressure at the cutoffs required for such a power output. I'd shave off 20-25% and use that as a constant power output.
All steam locomotives have the same horsepower. "0" when standing still
samfp1943 samfp1943 wrote the following post yesterday: TrAcKr76 What was the horsepower of these locomotives. I can't seem to find it anywhere. Thanks. Unfortunately, I cannot find a HP rating for these types.. You might be able to calculate it from the enclosed Stats?
TrAcKr76 What was the horsepower of these locomotives. I can't seem to find it anywhere. Thanks.
Ye gods, what a Chinese puzzle THAT set of 'explanations' is. They all make sense, mind you, once you understand what the mathematics and jargon involve. But for most of the people reading this, it doesn't even hint at the relative importance of the various factors. Astoundingly, it doesn't seem to be starting with a discussion of PLAN, the formula for INDICATED horsepower, which is what I'd have 'ballparked' as a first cut:
P = pressure, in American units (psi)
L = stroke in FEET (convert it from the usual measurement in inches);
A = effective area of the piston (remember the piston rod reduces this on one side of a double-acting locomotive, but relatively slightly), in square INCHES (don't ask me, consistency in units isn't supposed to be a feature of English units anyway);
N = number of power strokes per minute (note, this is NOT revolutions per minute; there are four strokes per revolution on a double-acting locomotive)
(P x L x A x N)/33,000 (correction for the definition of horsepower in English units) = desired horsepower.
The 'kicker' here is that P, the mean effective pressure, isn't easily measured at speed even with an indicator setup. Cutoff further affects it in several ways. The historical sources like Cole or Ralph Johnson used an empirical number for this by using some percentage (different, and more complexly derived, from the one used for TE calculation) of nominal boiler pressure. This is not as 'intellectually cheating' as it might appear, as many of the actual characteristics of the expanding steam in a working locomotive at speed can only be measured empirically anyway if you want more meaningful real results (the complicated mathematical modeling has so many assumptions that there often isn't adequate certainty it will be a good 'predictor')
This of course is somewhat like taking conditions for starting TE and adapting them for performance at speed ... don't expect the results to match what you actually would observe. Losses due to wall condensation and nucleate condensation (as work is extracted from the steam during the stroke), compression issues, wire-drawing due to port and other flow restrictions, etc. all affect how the steam actually produces engine power; boiler characteristics (hence the 'heating surface' adjustment made in some of the alternative formulae) determine whether adequate (and adequate-quality) steam will be produced at a given road speed. (Again, it would be nice if we could have test-plant data showing evaporation and steam quality, etc. for a given rate of steam supply.
Oddly enough, I believe one of the earliest test runs conducted on the PRR test plant at the exhibition at the beginning of the last century was for an ATSF 2-10-2, but not one that even remotely resembled a 'modern' design - IIRC it was a tandem compound with little or no superheat).
It's an odd thing, but horsepower ratings seem to be tough to find on any old steam locomotives,if you can find them at all. Horsepower just doesn't seem to show up at all in any specs until the late steam/ early diesel era. Maybe it just wasn't as important as tractive effort. Who knows?
What was the horsepower of these locomotives. I can't seem to find it anywhere. Thanks.
Unfortunately, I cannot find a HP rating for these types.. You might be able to calculate it from the enclosed Stats?
Here is a site for the USRA -Light- 'Santa Fe' 2-10-2 types @ http://wiki.healthhaven.com/USRA_Light_Santa_Fe
Here is a site for the USRA -Heavy- 'Santa Fe' 2-10-2 type @ http://wiki.healthhaven.com/USRA_Heavy_Santa_Fe
This is a link to J.D.H. Smith's site @ http://orion.math.iastate.edu/jdhsmith/term/slususra.htm
Then there is this site: @ http://www.steamlocomotive.com/santafe/?page=usra
It gives statistics for the Santa Fe Types of USRA Locomotives by 'Light' and 'Heavy'//Scroll down to the bottom and you will find the following Power Computations: Follow the top linked item (More Information) and you wil find @ http://www.steamlocomotive.com/llanso-power.php This linked site contains the Descriptions of Power Computations[ as arrived at below]
Introduction and roster provided by Richard Duley . Class details and specifications provided by Steve Llanso of Sweat House Media.
Hope this helps you!
As with other steam locomotives, the only way to learn its horsepower is to measure it. I've never seen a measurement for a USRA 2-10-2.
Good a guess as any: around 3000 hp at the driver rims at 30 mph?
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