Locomotive type selection for operation

[Anonymous]

Hi all, I've been reading MR for close to 50 years, and decided today to visit here. I tried the search function and found nothing on this topic, so please refer me if prior discussion exists. I am interested in both steam and diesel in the context of the questions.

In the interest of prototypical realism, I am looking for insight into how a railroad decides what type of locomotive to put on the front of a train. I have read various books such as the spottin guides and the cyclopedias, but they largely just describe the differences. For example telling me that a 4-8-2 evolves into a 4-8-4 by having a larger firebox than the 4-8-2. But nothing to tell me where each type is more appropriate.

I have no specific types in mind other than as examples. I am looking for general guidelines. My working impressions may be faulty. For example larger driving wheels would seem to be more for speed, while smaller drivers would be more for pulling tonnage. And having more drivers would seem to be a matter of getting more traction on the rails for a heavier load.

But the firebox issue is different. Would a larger firebox be more intended to be able to produce a lot of steam more quickly under demand or would it be for sustaining more heat over time? And boiler length in general is a question. A 4 wheel versus 2 wheel lead truck indicates to me a longer boiler. WOuld that be just to make more steam in a given period of time? Or does it affect the pressure in some way. I assume there would be greater surface area in the flues, but to what end.

Not looking for the physics of steam engines necessarily, just what goes into selecting a 2-8-4 versus a 4-8-4 versus a 4-8-2 or a 2-8-2.

ANd while diesels - road diesels anyway - seem to be more versatile, I still have to decide whether I send a GP9 or an SD9 out at the head of a freight train.. Does the six-axle truck spread the weight over more axles? or does it provide more driving wheels for more pulling power?

And while I am at it, my interest is mainly in the B&O, for whom my grandfather worked all his life. The B&O ran its GP diesels long hood forward like some others, while many other roads ran them short hood forward. For a model, external appearance doesn't change, but for interiors, were the locomotives manufactured with the cab fittings - controls and so on - "reversed" for those roads, or were they all the same and the engineer had to sit on the same side of the locomotive regardless?

Thanks for any responses.

[bogp40]

tmEnzo,
If you don't get the responses here, under modeling, try posting on the Trains magazine forum. Some of these guys live and breathe the real thing. I model the B&O myself, but some of these prototypical questions of yours are beyond my knowledge, especially steam. As to some of the diesel, I have seen most of the pics of early Geeps 7-9s, that there doesn't seem to be a preference as to long hood forward only or visa-versa. With the arrival of the GP30s it is rare to find one not running short hood. If I am wrong in my conclusion, I would definetly like to know the truth. Just going by pics may not be acurate assesment, if the photographer was looking for head end shots only.
As to the railroad using 4 or 6 axle, it has been my understanding that the 6 axle could pull more yet run on lighter rail or rail in poor condition with less chance of problems.
Other considerations as to engine selection, I believe is a case of use what's available at the time to do the job.
I would suggest that you look into the B&O yahoo groups, if you model the B&O these guys will blow your mind w/ their knowledge.
Welcome to the Forum.
Bob K.

[nbrodar]

I can't speak to steam, but I can give a brief overview of diesels.

Unitl the early 90s, 4 axles were prefered for high-speed service, because they tracked better at high speed. The advent of "steerable" 6 axle trucks doomed the 4 axles in most mainline service.

Early 6 axles were develeoped to a) spread the locomotive's wieght out, and b) provide more traction. The development of the SD40 and 45 began the evolution of 6 axles from slow drag engines to fast tonnage haulers.

Externally, there is very little difference in running long or short hood forward. The main difference is the internal cab layout. The controls are always (almost) on the right side of the can when facing forward. So long hood locos would have thier controls on the opposite side of the cab from short hood ones.

Nick

[TomDiehl]

On to the steam side of the question: Firebox size was a combination of factors. 1. the requirement for steam during heavy operation (which also dictated overall boiler size) 2. the grade of coal the railroad would be using in the firebox. For example, hard coal (anthracite) burns slower than soft coal (bituminous), so a larger grate area (bottom of firebox where the coal is actually burned) is needed. These large firebox locomotives were common in Pennsylvania, as on the Reading and DL&W. Plus the many grades of coal within the definitions or "hard" and "soft" coal. The size of the firebox would also dictate the number of trailing truck wheels, since the larger firebox wouldn't fit between the drivers on locos built in the 20th century. A short firebox would get a 2 wheel trailing truck, a large would get a 4 or even 6 wheel one.

The next part is general "rules of thumb:"

You're correct about the large and small driver sizes.

The choice of wheel arrangement and driver size would be based on the freight and passenger operations, factoring in the terrain over which the trains will operate. Long freights on a medium speed schedule (say around 50 MPH max) would get a smaller drivered loco than a fast passenger, scheduled for around 75-80 MPH top speed. Hilly terrain would cause the choice to go toward more drivers. For example, a drag freight over hilly terrain would probably get a Mikado 2-8-2 with aprox. 53 inch drivers, where a fast passenger over the same route would get a Northern 4-8-4 with aprox 80 inch drivers.

In the 30's locomotive manufacturers started adding appliances (car buffs would call these accessories) to increase the steaming and efficiency of locomotives. Superheaters, feed water heaters, thermic siphons, etc, some had parts exposed on the outside of the loco, some not.

[twhite]

Out here in the wild west, terrain has a great deal to do with what type of steam locomotive was chosen for specific consists. Not all railroads used a certain wheel arrangement for the same duties. For instance, the Southern Pacific used a 2-6-0 in the California Central Valley for heavy freight duties (the so-called "Valley Mallets") since the terrain was flat and the rail line relatively straight. Ordinarily, this wheel arrangement might be used for nothing heavier than light freight or switching duties.
So it pretty much depended on the railroad and the locomotives they ordered.
Here's a general overview of locomotive assignments--this is not specific to any particular railroad, however.
2-8-0: Switching or branchline freight
2-8-2: Medium freight
2-8-4: High speed or expedited freight
2-10-2: Heavy or drag freight
4-6-0: Light or local passenger
4-6-2: Local passenger or commuter service
4-8-2: Dual-service--passenger or freight
4-8-4: Through passenger or express
Mallet compounds (2-6-6-2, 2-8-8-0,2-8-8-2) usually drag freight or helper service
Simple Articulateds (2-8-8-2,2-8-8-4,4-8-8-2,4-6-6-4, 2-6-6-4, 2-6-6-6) Heavy mountain service, expedited freight or--in some cases-- through passenger.

As an example: The Southern Pacific Donner Pass line. Trains coming east from Oakland, CA would usually have their locomotives (4-8-2, 2-10-2, 2-8-2, etc) changed over to articulated 4-8-8-2's in Roseville, CA, at the base of the Sierra Nevada mountains. After climbing more than 6900 feet in a little over 80 miles on grades that often exceeded 2.4%, the 4-8-8-2's would be cut off at Sparks, NV, and the trains would be re-assigned to non-articulated locomotives (4-8-2, 2-10-2) for the trip across Nevada to the Union Pacific/Rio Grande connection at Ogden, UT.

For the trip across the Sierra, helper locomotives (2-8-0, 2-8-2, 2-10-2) would often be assigned to the articulateds at various points along the line.

This is just one example. Hope this helps a little.
Tom

[tomikawaTT]

Steam locomotive operations fell into several broad categories, determined entirely by service conditions:

Switching - lots of starting tractive effort. Most purpose-built switchers had 50-52 inch drivers and no lead or trailing trucks. They didn't need to be fast, just capable of moving a heavy load for a relatively short distance at low speed. Later in the steam era, some roads used otherwise-obsolete 2-8-0's for switchers. Mallet compounds were frequently used for hump engines, again for their ability to push a complete train up the grade to the crest of the hump.

Drag freight - Lots of tractive effort, speed not a requirement. 2 wheel lead truck standard, to assist in tracking. This called for drivers in the 56-63 inch range, and a boiler which would provide enough steam to maintain a speed of 20-25 MPH over the road. Normally found on coal drags (hence the name) and other non-priority freight.

Fast freight - 63-69 inch drivers, or more (N&W A 2-6-6-4 had 70", ATSF 2-10-4's had 74" drivers,) plus lots of steaming capacity. 2 wheel lead truck usual, sometimes 4 wheel used. Assigned to priority freight, where speed was a selling point.

Dual service - 68 inch or larger drivers, 4 wheel lead trucks. Capable of moving over the road quickly with a moderately heavy passenger or fast freight train.

Local passenger - 68" or larger drivers, 4 wheel lead trucks, high power for starting and accelerating from frequent station stops (think commuter service.) Long-term steaming capacity and super-high speed were not necessary. The PRR G-5s 4-6-0 was a very successful example.

Long distance passenger - 74" or larger drivers, 4 wheel lead trucks, big boilers, big tenders to maintain high speed with a standard passenger train and run a long way between fuel and water stops. Many on PRR and NYC were equipped to take water on the fly from track pans, so carried comparatively greater amounts of fuel and less water. (the N&W J was an exception, with 70 inch drivers, but it was so well balanced that it could cruise at 90mph and once reached 114mph on test.)

There is considerable blurring between the categories, because the road foreman of engines didn't always have the best loco for the job. Before the last of N&W's class A's were available, Y-class 2-8-8-2's were given merchandise trains, even though their top speed in that service was only 30-40 mph. Also on N&W, Class A 2-6-6-4's sometimes pinch hit for class J 4-8-4's. The 2 wheel lead truck didn't prevent the A from maintaining passenger schedule speeds.

Hope this helps. The best bet would be to check with the historical society of your favorite railroad for prototype-specific practices.

Chuck

[Anonymous]

Nothing to add to what twhite & tomikawaTT said about drivers - they covered the ground pretty thoroughly.

Just to expand a bit on the trucks. The leading trucks are for steering - they help guide the loco into a curve (see tomikawaTT's note on tracking). So the higher the speed, the more important the leading truck is.

Switch engines typically have no lead truck, as they are operating at low speeds - typical switchers are 0-4-0, 0-6-0 & 0-8-0.

Freight engines often have a 1-axle (2 wheel) leading truck, since they are operating at higher speeds, but not at the higher passenger train speeds . And passenger trains have 2-axle (4 wheel). Twhite gave a good list of typical wheel layouts for freight & passenger trains.

And the trailing truck, as others have stated, supports the firebox. For a switch engine, a large firebox is not required, so no trailing truck. For locals and short-haul work, 1 axle is adequate. For heavy drag freights or sustained high speed passenger work, a heavier 2 axle truck is needed.

Hope that helps put everything in perspective.

James

[wjstix]

Six axles diesels could come in two different styles. Some diesels had all three axles of each truck powered ("C-C") others used an unpowered set of wheels in the middle "A-1-A". The A-1-A trucks were used usually to help distribute the weight (where the lbs. per axle would be too much for the track if there were only four axles). It also helped tracking at highspeed apparently, since most passenger diesels (like General Motors "E-units") had A-1-A trucks.

For steam, which engine pulled a train came down to tonnage and speed. The engine would have to be powerfull enough to pull the weight of the train, which would be calculated as the train was being made up. (That's why freight cars have the light weight etc. stencilled on their sides.) Then it would depend on how fast it had to go. An express freight (like a train of all refrigerator cars with perishable cargo) might get a 4-8-2 or 4-8-4 with large wheels to pull it at 60 MPH, a general freight might get a low drivered 2-10-2 because it only had to go 20-30 MPH.

[Leon Silverman]

There was one notable exception to the rules presented above. There was a 4-12-2 and a 4-10-2 wheel arrangment used for freight engines. The reason for this was that these were compound steam engines that had three cylinders up front instead of the ususal two. The extra weight of the third cylinder with its accessories required the two axle lead truck. These were experimental designs that did not last too long because of the maintenence headaches associated with the third cylinder .

[marknewton]

UP & SP 4-10-2s and UP 4-12-2s were all simple expansion locos, not compounds. I wouldn't describe them as either experimental or shortlived - all three classes had long service lives. The SP 4-10-2s were very successful, as their assignmment meant that operating speeds weren't excessive, and the even torque of the three cylinders prevented undue staliing at slow speeds.

Cheers,

Mark.

[marknewton]

QUOTE: Originally posted by TomDiehl

In the 30's locomotive manufacturers started adding appliances (car buffs would call these accessories) to increase the steaming and efficiency of locomotives. Superheaters, feed water heaters, thermic siphons, etc,

All of these appliances predate the 1930s. In the US, superheaters were common on road power after the general adoption of the Schmidt-type return bend element in 1910. Feedwater heaters are even older in overseas practice, but became common in the US after 1920. Likewise, syphons, circulators and arch tubes were common overseas from the early 1900s onwards, and were adopted in the US around WWI.

Cheers,

Mark.

[Anonymous]

Thank you very much for the replies, that is good information to absorb.

Robert, regarding the B&O GPs, in my years watching them (during the 1950s) they might face either way in switching, but at the head of a train going somewhere, they almost always went long way first. Of course all that changed when they lowered the short hoods and added wide windshield windows to later models.

Much of my trackside time was spent in Brunswick, MD, watching the activity around the roundhouse and engine servicing facility. A lot of great places to see trains in the Potomac valley. The old roundhouse fell into ruin, sadly.

[Anonymous]

The knowledge here is impressive!

Mike in Tulsa
BNSF Cherokee Sub

[bogp40]

QUOTE: Originally posted by t.m.Enzo

Thank you very much for the replies, that is good information to absorb.

Robert, regarding the B&O GPs, in my years watching them (during the 1950s) they might face either way in switching, but at the head of a train going somewhere, they almost always went long way first. Of course all that changed when they lowered the short hoods and added wide windshield windows to later models.

Much of my trackside time was spent in Brunswick, MD, watching the activity around the roundhouse and engine servicing facility. A lot of great places to see trains in the Potomac valley. The old roundhouse fell into ruin, sadly.

t.m.Enzo,
Thanks for that first hand info on the road units. Great to hear it from from someone who saw them in operation. They were before my time, and I need to gather info from people that were there. Pleased to see so many replies to the steam questions, very informative, this Forum.....
Bob K.

[TomDiehl]

QUOTE: Originally posted by marknewton

QUOTE: Originally posted by TomDiehl

In the 30's locomotive manufacturers started adding appliances (car buffs would call these accessories) to increase the steaming and efficiency of locomotives. Superheaters, feed water heaters, thermic siphons, etc,

All of these appliances predate the 1930s. In the US, superheaters were common on road power after the general adoption of the Schmidt-type return bend element in 1910. Feedwater heaters are even older in overseas practice, but became common in the US after 1920. Likewise, syphons, circulators and arch tubes were common overseas from the early 1900s onwards, and were adopted in the US around WWI.

Cheers,

Mark.

The development, true. But the widespread uses, especially in combination, is what started the "superpower" era (no not the Marvel Comics one).