Steamers vs Diesels...pulling power?

[Jacktal]

This week,I tested my DCC converted N scale Challenger on the club's layout and have been delighted by flawless running,which makes the conversion complexity worthed it.

After a little while,I elected to test its power by adding cars and having it pull the string up the layout's "Peninsula climb",which is the most demanding section of our N scale layout.Amazed I was by how powerful this baby is as I added 18 cars to it without any real sign of being overloaded while my other strongest locos (Kato SD-90's) can't reach the top of the hill with only 12 cars.They start spinning and speed soon fades away.

I understand that the difference is in the traction,as the Challenger probably is heavier (I didn't weigh them) and the fact that it's wheel diameter is larger may affect also,since both have 12 wheel drive.

But this got me wondering if this was also true in the real life,meaning that a steamer would in many cases have much more pulling power than many big diesels.If so,then how many big D's would it take to match let's say a Big Boy?

[twcenterprises]

I think I remember reading somewhere that a Big Boy could pull over 100 loaded reefers at over 100 MPH. Assuming 50 tons (cargo) per car plus empty weight of 25 tons each, that would equate to 7500 tons. It would probably take at least 3 modern SD's to pull that tonnage, and not even at the same top speed.

On the other hand, Southern Railway had 2-8-2 Mikado's running on the "Rat Hole" division, which were rated at 1750 tons on the division. When the FT's first arrived on the scene, a 4 unit set was rated at 3000 tons on the same division, and saved over an hour on the running time (presumably, no fuel and water stops).

Keep in mind today's railcars are much heavier than those of the '40's and '50's, so a train of the '50's with 50 cars may weigh 3750 tons (at 75 tons per car), a modern train with 50 cars may weigh 6250 tons (at 125 tons per car).

Brad

[Anonymous]

Sorry Jacktal,

I love steam engines too, but more like the other way around. How many big boys to match one diesel? However, I do not know.

If steam engines really had a big advantage in power do you think the world's railways would have changed? Especially in countries where coal is plentifull but oil has to be imported. Maintenance was a drawback with steam engines, but if they were much more powerful than diesels they could have found a way around that.

Sorry, the steam engine is spectacular but far less efficient and effective than a diesel electric. Of course if you put wires overhead you can dice the diesel part. Just electric and that is efficient (apart from the cost of those wires)!

[wjstix]

Only the latest generation of diesels can match the most powerful steam engines one on one. On level track, a UP 4-8-8-4 could pull a train 5 miles long by itself. I seem to remember reading somewhere that an FT A-B set had about the same pulling power as a 2-8-0 or 4-6-0, and a 4-unit A-B+B-A set was like a 2-6-6-2 or 2-8-8-2 mallet.

The primary advantages diesels had over steam was greater availability - being able to make more runs per week or month than steam, and greater flexibility - you could use 1 diesel or 10 depending on how much power you needed...and only use one crew instead of one for each engine. But generally you had 3-4 diesels taking the job one steam engine had performed.

[Jacktal]

Why steamers were dropped isn't even questionable.These beasts were messy,noisy,took a long time to get started and needed outrageous maintenance so no wonder why railways gladly parted with them when another option became available,even when considering their immense power.

But as wisely stated,I don't think railways were too glad to lose all that power,wich pretty much explains the births of other very unique designs like the Veranda's,GE'S Turbines and the DD series wich in fact were experiments trying to obtain the best of both worlds.But still,these all died for mostly the same reasons the steamers did,being mostly maintenance,fuel costs,noise and lack of flexibility and/or efficiency.

Now we have reached an era where even diesel's days are counted,being replaced quite efficiently by electric powerhouses in many countries who are more and more aware of the pollution damages.They are a lot less noisy and messy and their maintenance is much simpler too.The electric traction motors have been here for decades so the only thing that keeps diesels alive are the enormous costs of building the network of supply lines.

I love steamers for modeling purposes indeed,but would certainly hate to have a Big Boy pass three hundred feet from my home ever so often.But i feel that steamers had a character of their own.

[Anonymous]

QUOTE: Originally posted by twcenterprises

I think I remember reading somewhere that a Big Boy could pull over 100 loaded reefers at over 100 MPH. Assuming 50 tons (cargo) per car plus empty weight of 25 tons each, that would equate to 7500 tons. It would probably take at least 3 modern SD's to pull that tonnage, and not even at the same top speed.

I don't know how accurate is the info on Wikipedia, but according to the articles there the Big Boy tops out speedwise at around 80mph (and its TE reaches a maximum of 135,000 pounds at a lower speed range, around 40mph or so).

If the Wiki TE figures are right, then one of the more modern 6-axle AC-traction diesels should give the Big Boy a run for its money.. I seem to recall the GE AC4400CW can develop a maximum TE of around 140,000lbs.

[edkowal]

Many steam locomotives had six figure tractive efforts.

UP Big Boy with 135,000 lbs.
N&W Jawn Henry 180,000 lbs.
N&W Y6b with 170,000 lbs.

Others had lower values:

N&W J with 80,000 lbs.
PRR J-1 with 95,100 lbs.
PRR I1sa with 96,000 lbs. etc.

The above values come from this site: http://www.steamlocomotive.com/misc/largest.shtml


For diesels:

SW-1500 with 42,000 lbs.
RS-3 with 62,125 lbs.
SD40-2 with 83,000 lbs.
SD70MAC with 137,000 lbs.
GE Evolution series 166,000 lbs.

So, as you can see, initially, diesels could not compete with steam engines on tractive effort, one for one. But there were many other reasons which tilted the balance, some of which were mentioned in other posts here. A good list of many of the reasons can be found in answer 11 at this site: http://exotic.railfan.net/dieselfaq.htm

-Ed

[jimrice4449]

Hey guys, 2 points. First who ever designed a road diesel to be regularly operated as a single unit? Here in God's Country the Milw took delivey of one of the first FT sets (ABBA) to run in the non-electrified gap between the Rocky Mountain Divn and Coast Divn electrified zones. One of the first changes they made was to the number board on the nose door. It originaly read 40. They changed it so that it could, by slipping in the appropriate letter, read 40, 40A or 40D because they found that generally two units could handle trains that previously had been handled by a Mikado or 2-6-6-2. (In train order territory on most roads the train was identified by engine number in which case you wouldn't want two different trains running around the RR identified w/ eng.40)
Another factor nobody is addressing is the difference in series and parallel wiring on a diesel. To start, their motors are connected in series which provides maximum torque. After the train gets a roll on the wiring is changed (called transitioning) to parallel which utilizes the engines HP to provide speed. A modern steam engine could produce around 6000 HP, but only after it got up to speed (40 to 60 MPH depending on the engine). The diesel could exert maximum HP to start.

[DSchmitt]

QUOTE: Originally posted by jimrice4449

Another factor nobody is addressing is the difference in series and parallel wiring on a diesel. To start, their motors are connected in series which provides maximum torque. After the train gets a roll on the wiring is changed (called transitioning) to parallel which utilizes the engines HP to provide speed. A modern steam engine could produce around 6000 HP, but only after it got up to speed (40 to 60 MPH depending on the engine). The diesel could exert maximum HP to start.

I read somewhere "a steam locomotive can pull a train it can't start, a diesel locomotive can start a train it can't pull."

---------------

In actual practice during the steam/diesel transition period railroads found that diesel lash-ups, in most cases, could haul heavier trains at higher average speeds with lower costs than the steam locomotives they replaced.

On some grades railroads were able to eliminate helpers and at the same time maintain faster schedules.

One book which addresses this is D Day on the Western Pacific by Virgil Staff.

[BigJim]

QUOTE: In actual practice during the steam/diesel transition period railroads found that diesel lash-ups, in most cases, could haul heavier trains at higher average speeds with lower costs than the steam locomotives they replaced.

I guess you haven't read the reports of the N&W's Steam/Diesel comparision.

In actual practice, you need to compare the tonnage rating of each locomotive from employee timetables.
For example, the tonnage rating between Roanoke and Waynesboro, Va. for one N&W Improved Y5/6 was 3200 tons. The tonnage rating between Roanoke and Waynesboro, Va. for one GE Dash 9 or EMD SD70 is 2950 tons.
NUFF SAID!!!

[Mark300]

QUOTE: Originally posted by DSchmitt

QUOTE: Originally posted by jimrice4449

In actual practice during the steam/diesel transition period railroads found that diesel lash-ups, in most cases, could haul heavier trains at higher average speeds with lower costs than the steam locomotives they replaced.

And use 1 crew instead of a crew per engine. Also a big incentive to use diesel lashups.

Mark

[BigJim]

FYI, real railroaders refer to their set of units as a consist, not a lashup.

[edkowal]

QUOTE: Originally posted by Jacktal

But this got me wondering if this was also true in the real life,meaning that a steamer would in many cases have much more pulling power than many big diesels.If so,then how many big D's would it take to match let's say a Big Boy?

It might be useful at this point to revisit the original question on the thread, as quoted above.

-Ed

[twcenterprises]

QUOTE:

QUOTE: Originally posted by twcenterprises

I think I remember reading somewhere that a Big Boy could pull over 100 loaded reefers at over 100 MPH. Assuming 50 tons (cargo) per car plus empty weight of 25 tons each, that would equate to 7500 tons. It would probably take at least 3 modern SD's to pull that tonnage, and not even at the same top speed.

I don't know how accurate is the info on Wikipedia, but according to the articles there the Big Boy tops out speedwise at around 80mph (and its TE reaches a maximum of 135,000 pounds at a lower speed range, around 40mph or so).

If the Wiki TE figures are right, then one of the more modern 6-axle AC-traction diesels should give the Big Boy a run for its money.. I seem to recall the GE AC4400CW can develop a maximum TE of around 140,000lbs

That may be accurate, my recollection is somewhat dated.

QUOTE:

QUOTE: On the other hand, Southern Railway had 2-8-2 Mikado's running on the "Rat Hole" division, which were rated at 1750 tons on the division. When the FT's first arrived on the scene, a 4 unit set was rated at 3000 tons on the same division, and saved over an hour on the running time (presumably, no fuel and water stops).

Another factor nobody is addressing is the difference in series and parallel wiring on a diesel. To start, their motors are connected in series which provides maximum torque. After the train gets a roll on the wiring is changed (called transitioning) to parallel which utilizes the engines HP to provide speed. A modern steam engine could produce around 6000 HP, but only after it got up to speed (40 to 60 MPH depending on the engine). The diesel could exert maximum HP to start.

That probably accounts for the running time difference, too.

QUOTE: One of the first changes they made was to the number board on the nose door. It originaly read 40. They changed it so that it could, by slipping in the appropriate letter, read 40, 40A or 40D because they found that generally two units could handle trains that previously had been handled by a Mikado or 2-6-6-2.

QUOTE: And use 1 crew instead of a crew per engine. Also a big incentive to use diesel lashups.

I recall reading early FT's being sold in sets of 2, 3, 4, or more, usually connected by drawbars instead of couplers. The whole setup was called a "locomotive", and each individual one was a "unit"; thus we have A units, and B units. Initially, many railroads (rightly) feared unions would say each unit with a different number was in fact a different locomotive, and their jobs should be protected (in other words, a crew in each UNIT.) This was avoided when, as drawbars were replaced by couplers, the units were numbered with a, b, etc., suffixes, so that when 3 or 4 units were coupled, the consist only needed one engineer and unions did't have any recourse. Of course, later, as crews got used to the "new" diesels, and the unions didn't object, the RR's usually renumbered the diesels as new units arrived.

At least, that's how I understand it.

Brad

[Anonymous]

One other point is that the newer diesels have advanced wheel-slip contol.

BTW, I think the SD70ACe has 180,000 starting TE and around 150,000 continous.

[wjstix]

FT's were designed by GM to only be made as A-B sets connected by drawbars - in fact, there were no doors between the A and B unit, so if they had to be separated for some reason, their interiors would be open to the elements. The Santa Fe asked GM to make individual FT's available, so they rigged up a way to add couplers to replace the drawbars. I think Santa Fe did some coupler modifications themselves.

The problem was that many railroads found one FT A-B set to not be powerfull enough for a typical train, but an A-B+B-A set to be too much power. The RR's really needed three units (4050 HP). GM did make some A-B-A FT sets for a couple of roads, but many roads after WW2 bought F2's A-units and added them to FT sets in A-B+A configurations on their own. These sets were sometimes called "FT-2's".

[Mimbrogno]

Something that needs to be brought up here is that tractive effort alone is not sufficient measurment alone to measure a locomotive. True, it is an excellent indication of it's starting capacity, but it is not as exact as you might think. Believe it or not, every TE rating you see out there is measured directly from the weight on drivers. Many, many years ago when railroads were in their infancy, tests were done to establish in definate measurments how much a locomotive could pull. It was soon realised that the only factor that affected traction with relation to weight is the adhesion or "stikyness" of the surface of steel on steel. It was decided at the time of the testing to fix the formula for tractive effort slightly less than the percentage of adheasive force of steel on steel, to 25% and 30% of the total wieght on drivers. With the advent of creep control, another set of tests discovered that slightly better traction was developed, and a new standard measurment of 35% for AC creep control locomotives was instituted. These mesurements are standard across the board, for steam, diesel, electric, pnumatic, and all other kinds of locomotives.

What this means in effect is that no matter what two engines you compare, if they have the same weight on drivers, the both have the same starting tractive effort. and to an extent, they can both (in theory) move the exact same load over the same terrain.

This flat measurement is inherantly inaccurite. There are in reality dozens of factors in addition to weight that affect traction. For the sake of expediancy the FRA and NAR decieded to adopt this flat rate measurement, instead of subjecting ever single locomotive to a battery of tests every time it came out of the shop and may have had some of those factors altered by new parts. You see, it's not just weight or the trucks that influence traction, its also the maintance that goes into it. Things like how the springs in the running gear are tensioned or the way wheels and axles are aligned, or how counterbalences are placed all affect the total effective drawbar pull.

While the variables mentioned above have only a minor affect on the total pulling power of the locomotive, there are some more permant variables that with significantly influnce the engines capabilities. The overall design of a diesel's trucks, or the diameter of the driving wheels and creep control are some of these more important factors. While I feel it would be worthwhile to account for some of these factors in the stated traction rating, (especially the design of the truck's suspension, I'll explain that later) most times only the very basic measurment is used.

I want to address the issue of wheel slip and creep control next. Some time ago it was discovered that in the breif time that the wheel is regaining grip on the rail after it has slipped, it actually has slightly better adheasion than normal. From this idea creep control was developed. This maintains the torque of the wheels at a point right at the force needed to begine slipping. It works in a pulse form, surging and cutting power very rapidly, so that the wheel slips for just an instant, and then the power is reduced so the wheel can regain its grip. This creates a sort of grinding motion, as opposed to a pure slipping motion where the wheel simply slides on the rail.

Steam engines, especially the two cylinder type, have their own sort of "creep control", as they have 2 double acting cylinders aligned 90 degrees apart. As the piston produces it's maximum power just after the steam enters the cylinder (in the middle of the stroke), and then loses all of it's power at the end of the stroke where it changes direction, you have one power surge per revolution for a single action piston. For two double action pistons (the universal kind on locos), you get 4 surges per revolution. However, this is actually a bag thing, as the surges are spaced so far apart and are so powerful that the wheel can spend more time slipping than gripping, and the power range of the surge, going from full to none and full again leads it more prone to slipping as you try to apply enough power to start a train. As a result, steam engines are in practice rated less than their diesel counterparts, using the 22% rating insted of the usual 25%. Steam engines with more than 2 cylinders have a less severe surging action, and as a result are far less prone to slipping. Steam engines with 4 cylinders and drive rods per wheel set, thus having 8 overlaping power surges, has a surge amplitude (difference between minimum and maximum power of the surge)  of only 80% - 100%, instead of the 2 cylinder's 0% - 100%. I know it's a bit complicated, but basically the more cylinders, the smoother the start and the less slipping. Early diesel switchers were so powerfull because they practically didn't have surging, and so were less prone to slipping.

There's a lot more I have to add to this subject, but I think I'll do so in another post, this one's already the size of a textbook. I will leave you with this note though, even though two different locomotives with the same starting TE could move the same train into motion, that doesn't mean they can get them up to the same speed.

Matthew Imbrogno
Mechanical Vollenteer, Arizona Railway Museum. 

[tomikawaTT]

During the transition era, the largest, most modern steam locos had both higher starting tractive effort and higher sustained horsepower than any SINGLE UNIT diesel then available.  However, most railroads were not replacing Big Boys, Niagaras and Y6b's.  They were replacing USRA-vintage and older locos, many of which had been run to the verge of collapse coping with WWII traffic.

For that matter, different steam locos developed their maximum horsepower at different speeds.  The N&W Class A 2-6-6-4 could measure 6300HP at the drawbar at 50mph, and would lose power as speed came down.  The same road's Y6 class developed its maximum horsepower, about 5400, at 25MPH.

Diesel locos develop their maximum horsepower standing still - or running at track speed.  Since the electric drive de-couples the prime mover from the wheels, changing speed does not result in changing horsepower.  Electric drive also provides a smoother application of power to the rails, resulting in a better adhesion factor than the 20-25% (of weight on drivers) common to steam locos.

It's not really fair to try to compare 21st century diesels to steamers withdrawn from service half a century ago.  Had reciprocating steam locomotives continued to evolve and develop, who knows what the combined ideas of Chapelon, Porta, Withuhn and others might have produced.

Chuck

[boxcar_jim]

It's not really fair to try to compare 21st century diesels to steamers withdrawn from service half a century ago.  Had reciprocating steam locomotives continued to evolve and develop, who knows what the combined ideas of Chapelon, Porta, Withuhn and others might have produced.

Quite so - just look at the "gas burner combustion" and other work done on South African Railways in the 1980s. In the prototype SAR "Red Devil" 4-8-2 efficency improvements over a standard SAR mountain was something like an 80% improvement in water and coal consumption (approx figures - I'm sure if someone looks this up on Wikipedia they can get the exact figures). However in order to get these improvements they had to use expensive bearing and alloy technologies, and double maintenance schedules, so ultimately diesel and electrics won the day.

[marknewton]

The significant changes David Wardale made to the Red Devil were mostly related to the firebox, boiler and steam circuit. None of this required "expensive bearing and alloy technologies" - what is your source for that claim?

Maintenance of the Class 26 was not greatly increased over a conventional steam loco, in no small part because the loco did not need to be flogged to achieve high performance.

From talking to Mr Wardale, and reading his book, it is apparent that as in so many other cases, the decison not to proceed with steam development was based on political, not engineering, factors.

Cheers,

Mark.

[Anonymous]

Pardon me, but isnt the SAR Red Devil a 4-8-4? I remember seeing it on TV and I thought it was a 4-8-4. I also remember, while it had good performance at high speed, at slow speed w/ a heavy load it had so much power that it slipped a lot.

[marknewton]

Yes, it was. I missed the OPs' reference to it being a 4-8-2, otherwise I'd have corrected it myself.

I don't recall offhand how the engine performed at low speed with a heavy train. I'd have to re-read Wardale's book before I'd comment.

Cheers,

Mark.

[boxcar_jim]

Yes, it was. I missed the OPs' reference to it being a 4-8-2, otherwise I'd have corrected it myself. I don't recall offhand how the engine performed at low speed with a heavy train. I'd have to re-read Wardale's book before I'd comment. Cheers, Mark.

Quite correct - don't know why I was thinking it was a Mountain in my early post. 

. I also remember, while it had good performance at high speed, at slow speed w/ a heavy load it had so much power that it slipped a lot.

I remeber reading this too.

Most of the info I have on the Red Devil came from a British mag article - which I now can't find! I have also read Mr Wardale's book - but years ago. I agree that most of the improvements were in the firebox and steam circuit (I have seen the gas producer/burner system in operation on the Ffestiniog Railway), but I definitely recall reading about improvements to the bearings and alloy lightweight side rods (and the inability of the local maintenance crews to cope with this).

However, all this is secondary to the point which was being made and discussed, that it was unfair to compare today's diesel/electric power with its on board microprocessors, with 50-100 year old technology. The Red Devil improvements just go to show that once modern engineering technology was brought to bear, reciprocating steam was suddenly much more efficient.

 

[marknewton]

boxcar_jim wrote:"Most of the info I have on the Red Devil came from a British mag article - which I now can't find! I have also read Mr Wardale's book - but years ago. I agree that most of the improvements were in the firebox and steam circuit (I have seen the gas producer/burner system in operation on the Ffestiniog Railway), but I definitely recall reading about improvements to the bearings and alloy lightweight side rods (and the inability of the local maintenance crews to cope with this)."

Yes, I recall reading this myself, now that you mention it. I'll have to find the book and read it again!

"However, all this is secondary to the point which was being made and discussed, that it was unfair to compare today's diesel/electric power with its on board microprocessors, with 50-100 year old technology. The Red Devil improvements just go to show that once modern engineering technology was brought to bear, reciprocating steam was suddenly much more efficient."

Absolutely, couldn't agree more!

Cheers,

Mark.