TAKING A BREAK

[Chromatix]

Quote:

no traction motors to overheat and burn out

No, but instead the transmission oil heats up and can decompose if it gets too hot. Roughly speaking, a torque converter peaks at about 80% efficiency and a fluid coupling peaks at about 90%; the latter doesn't have the former's torque-multiplication capability, so it tends to get used for the higher "gears" where efficient cruising is wanted rather than maximum haulage.

You'd think that cooling that oil would be easy in, say, Finland, but the ubiquitous Dv12 locos here are restricted to only short periods of heavy shunting duty, interspersed with long periods of cooling off. They can operate at full power continuously only when hauling a train on the main line at a reasonable speed. At the low speeds involved in shunting duty, a torque converter operates at much less than its peak efficiency, resulting in more waste heat. Now the Dv12 isn't a very large loco, making I think 1000-1200hp at the prime mover, which is in the range where hydraulic transmissions are considered relatively easy to build. A few of the type have been specially fitted with enlarged oil coolers so they are less restricted in shunting duties; the newer diesels however have electric transmission.

The most obvious solution to the power-handling problem is to increase the number of transmissions involved, directing only some of the total engine power to each. The early approaches to this involved fitting two complete engine-transmission sets to each loco, each driving one bogie. I believe there are now some locos in service with one big engine and a dual transmission. In principle a triple transmission could also be built on a B-B-B (three bogies) wheel arrangement, but nobody's been crazy enough to try it yet; even the Japanese, who have plenty of Bo-Bo-Bo electrics in service, limit themselves to a C-B (five axle) diesel type.

Where hydraulic transmission *does* have an advantage is in power to weight ratio. This makes it a natural choice for multiple-unit trains, where the engine stuff is mounted below the solebar. Voith Turbo make a whole range of standard transmissions to fit such trains, usually with one torque converter for starting and one or two fluid couplings for higher speeds. Here's one of their older T211r transmissions in action.

[whartung]

How was the body made BDD?

[BigDumbDinosaur]

Chromatix wrote:

Quote:

no traction motors to overheat and burn out

No, but instead the transmission oil heats up and can decompose if it gets too hot.

Yes, that can happen. Modern synthetic oils can better tolerate the heat, but there are limits.

Quote:

Roughly speaking, a torque converter peaks at about 80% efficiency and a fluid coupling peaks at about 90%;

Actually, a fluid coupling can achieve even higher efficiency. The General Motors Hydra-Matic transmission, which used a fluid coupling and a four-speed gearbox, was claimed to achieve 96-97 percent efficiency in fourth gear. The manufacturer of the fluid coupling in my locomotive claims 95 percent efficiency when running under maximum rated loading and RPM (however, I intentionally overload the coupling to better simulate the behavior of Diesel-electric operation).

The efficiency of a fluid coupling inversely and exponentially varies with the input-to-output speed differential, as well as the absolute input speed—this characteristic is explained here. In contrast, the efficiency of a torque converter resembles an inverted U. Once a torque converter comes out of stall, efficiency rapidly rises until the input-to-output speed differential reaches 80-85 percent. At that point, the return oil flow from the turbine (driven member) to the pump (driving member) significantly diminishes and the stator imposes parasitic drag. Practical converters mount the stator on a one-way clutch so it can rotate with the pump during light loading. The clutch, of course, prevents contra-rotation during the torque multiplication phase.

Quote:

You'd think that cooling that oil would be easy in, say, Finland, but the ubiquitous Dv12 locos here are restricted to only short periods of heavy shunting duty, interspersed with long periods of cooling off.

Oil-to-air heat transfer is never very good. I've seen solutions in some industrial installations in which the oil is passed through a water-cooled heat exchanger and the water, in turn, is cooled by a conventional radiator. Such an arrangement isn't very practical with a locomotive.

Quote:

The most obvious solution to the power-handling problem is to increase the number of transmissions involved, directing only some of the total engine power to each.

That, of course, adds complexity and doesn't actually do anything for the efficiency issue. It merely distributes the losses, versus concentrating them in a single unit.

Quote:

Where hydraulic transmission *does* have an advantage is in power to weight ratio.

At least in North America, that is a secondary design consideration, especially in freight locomotives. As the old saying goes, weight is your friend in a locomotive. The factor of adhesion is strongly bound to the total weight on the driving wheels. Given what we expect from our freight locomotives, builders design to use the maximum possible axle loading that the track can tolerate, typically 70,000 pounds (31,818 kilograms) per wheelset on 141 pound rail.

The bottom line is electric power transmission continues to be the most efficient way to get the prime mover's output to the wheels.

[Chromatix]

You're right, increasing the number of transmissions does nothing for efficiency, but it *does* allow installing more power in a single locomotive than a single transmission can handle.

On the other hand, most European railways have moved to electric traction (with overhead wires and so on) instead of building ever bigger diesel locos. American railways are a weird outlier in that respect.

[BigDumbDinosaur]

whartung wrote:

How was the body made BDD?

Along with everything else in the locomotive, I built the body in my shop.

The main part of the body is made from laser-cut sheet steel, with an internal "skeleton" to give it structural integrity. Welded construction is used wherever steel is joined to steel. Here's a picture of the skeleton right after I finished welding and cleaning it.

Body Skeleton

The nose assembly, which is essentially everything from the cab doors forward, is a one-piece Alumilite casting. It is bonded to the rest of the body with PC-7, a high-strength epoxy. Here's a picture of the casting.

Alumilite Nose Casting

Here's are some photos in which I am building up the body in my shop.

Roof Attached to Skeleton

Side Panels Attached to Skeleton

Built-Up Body

The below photo shows the body mounted on the chassis and opened. As the body weighs around 110 pounds, I used a pair of industrial gas springs to lift and support the body in the open position.

Body on Chassis, Opened

Incidentally, I have a topic on Chaski which goes into considerable detail about this project.

[whartung]

Chromatix wrote:

You're right, increasing the number of transmissions does nothing for efficiency, but it *does* allow installing more power in a single locomotive than a single transmission can handle.

Most of the diesels here are electric, as I understand it. I don't know what kind of gear reduction is necessary between the diesel motor and the on board generator.

Obviously, models like BDD aren't necessarily this way, but they're not hauling a 100 cars up a mountain pass either.

Our local park has a small locomotive. It's propane/natural gas as far as I can tell. It "looks" like a steam train, in that you have reciprocating drivers and drive wheels.

We have enough of a grade in the park that the locomotive has a sand system the engineer can use on heavy days.

I think it's 4 cars, 6-7 rows each car. They call it 1/3rd scale.

[Chromatix]

Generally the generator (actually an alternator in "recent" models dating back 40 years or so) is designed to run at engine speed and is directly mounted on the end of the crankshaft, with a pass-through shaft so that smaller auxiliary generators can be mounted to it in the same way. Depending on the engine, that could be as little as 850rpm (eg. English Electric RKT series inline and V engines, Sulzer LDA series inline and H engines) at full power; many cars idle faster than that.

The low-speed engines I mentioned above were principally designed for direct-drive marine service, where great reliability and immense torque at low RPM was needed for the propeller shaft.

These days locomotive engines tend to be medium-speed designs running up to about 2000rpm or so. This speed range is also more-or-less ideal for hydraulic transmissions.

[whartung]

BigDumbDinosaur wrote:

The nose assembly, which is essentially everything from the cab doors forward, is a one-piece Alumilite casting. It is bonded to the rest of the body with PC-7, a high-strength epoxy.

Did you make the casting, or was this a piece you purchased?

[BigDumbDinosaur]

Chromatix wrote:

On the other hand, most European railways have moved to electric traction (with overhead wires and so on) instead of building ever bigger diesel locos. American railways are a weird outlier in that respect.

I see this sort of comment posted all the time by railroad enthusiasts outside of North America. It indicates to me that they don't understand the scope of North American railroad operations and the economy they support, or the economics of electric traction versus Diesel-electric traction.

Consider that the United States' conterminous land area is approximately 3.1 million square miles, roughly 79.5 percent of the land area of the entirety of Europe. Our freight railroads operate over about 140,000 route-miles of track and reach virtually every corner of that land area. In doing so, they must traverse terrain that varies widely in both topography and climate. As our population density is far lower than that of Europe's, most long-haul rail lines run through sparsely populated areas.

In Canada, the Canadian National and Canadian Pacific railways, the dominant freight carriers, operate a combined 32,900 route-miles and in equally challenging conditions (both also operate in the USA and some American lines operate in Canada). In fact, the Canadian Rockies pose one of the most difficult environments in the entire world for freight railroading, with huge amounts of snowfall in the winter, extremely cold temperatures and many heavy grades.

Distance, topography, climate, catenary power transmission limitations, and basic economics are the factors that explain why most North American rail lines are not electrified. Aside from the initial (and HUGE) capital expenditure required to install the catenary, its supporting structure, the power distribution network and, of course, the generating stations on routes that may stretch nearly 1500 continuous miles (for example, the BNSF route from Minneapolis to Seattle), there is the difficulty and expense associated with maintaining the infrastructure, especially in remote areas with weather extremes.

In addition to the above, North American freight train density is high on most mainlines, and the trains themselves are often very long and extremely heavy. Few European railroads operate trains that approach the lengths and weights that are routine here. For example, a typical train hauling coal from the Powder River Basin (located in southern Wyoming and northern Montana) may consist of 125 cars, each loaded with 100 tons of coal. The gross weight of such a train will be around 16,250 tons and will typically have a length of approximately 6,800 feet. On average, about 15,000 to 17,000 horsepower (11.2 to 12.7 megawatts) is required to start such a train and haul it at "track speed," which is typically 70 miles per hour on the long-haul mainlines. As train separation may be as short as 10 minutes on heavily-used routes, the loading on the catenary and distribution network would likely be impractical, were the line electrified.

Another issue is reliability and its effects on the ability of rail lines to operate. Electrification can be failure-prone due to extreme weather conditions that are often encountered in the winter. Lines come down due to ice formation, snow can infiltrate equipment enclosures and short out things, etc. On heavily-used lines, such as the aforementioned BNSF line, a catenary failure would be a major problem. Much of that route is single-tracked with passing tracks (sidings), which means if a train is stalled on the mainline due to catenary power loss, the entire line will become backed up for hundreds of miles in both directions. All it would take would be for one catenary substation to go off-line to stop everything.

Contrast that with operating with Diesel-electric power. Multiple Diesel-electric locomotives, in addition to producing power levels that are not usually attainable on an electrified line, offer redundancy. On level terrain, as long as at least one locomotive is operating normally, a train will likely be able to keep moving and get to where the dead unit(s) can be set out and replaced. A railroad doesn't have that option on an electrified line if catenary power fails.

Redundancy, along with the aforementioned costs of electrifying, is why we continue to use Diesel-electric power.

[BigDumbDinosaur]

whartung wrote:

BigDumbDinosaur wrote:

The nose assembly, which is essentially everything from the cab doors forward, is a one-piece Alumilite casting. It is bonded to the rest of the body with PC-7, a high-strength epoxy.

Did you make the casting, or was this a piece you purchased?

I purchased it.

[BigDumbDinosaur]

whartung wrote:

Chromatix wrote:

You're right, increasing the number of transmissions does nothing for efficiency, but it *does* allow installing more power in a single locomotive than a single transmission can handle.

Obviously, models like BDD aren't necessarily this way, but they're not hauling a 100 cars up a mountain pass either.

Not yet! However, during initial proof-testing the design I did haul a pretty long train, which also had several dead locomotives in the consist to add weight. We calculated the total train weight to be 7800 pounds, which is quite a bit to be hauled by a locomotive producing about 16 horsepower. The ruling grade at our railroad is 2.7 percent, so it got interesting as the train ascended the grade.

Long Test Train

Long Test Train

In the above photos, note the position of the orange covered hopper car, which will give you an idea as to how long a train this was. That car is visible in the first picture in the same field of view as the block signal on the other track.

Long Test Train Climbing 2.7 Percent Grade

I took the above photo as the test train was about to crest the 2.7 percent ruling grade.

[whartung]

BigDumbDinosaur wrote:

In fact, the Canadian Rockies pose one of the most difficult environments in the entire world for freight railroading, with huge amounts of snowfall in the winter, extremely cold temperatures and many heavy grades.

Roger's Pass and Big Hill. To quote Gandalf: "You! Shall not! Pass!" to wit Canadian railroad engineers said, "Here, hold my beer."

Quote:

For example, a typical train hauling coal from the Powder River Basin (located in southern Wyoming and northern Montana) may consist of 125 cars, each loaded with 100 tons of coal. The gross weight of such a train will be around 16,250 tons and will typically have a length of approximately 6,800 feet. On average, about 15,000 to 17,000 horsepower (11.2 to 12.7 megawatts) is required to start such a train and haul it at "track speed," which is typically 70 miles per hour on the long-haul mainlines.

When you stand next to one of the monster (no, really, monster!) Cab Forward mountain steam locomotives that they used to use in the Sierras, you're truly standing in the shadows of greatness. They have one in the Sacramento train museum.

Of course the modern GP D-E locomotives crush even these goliaths.

Rockies and Sierras are no joke. Running still on 150 year old right of ways and earthworks.

[floobydust]

Great Pics! Awesome project!! Thanks for sharing such a cool project.

[BigDumbDinosaur]

whartung wrote:

When you stand next to one of the monster (no, really, monster!) Cab Forward mountain steam locomotives that they used to use in the Sierras, you're truly standing in the shadows of greatness. They have one in the Sacramento train museum.

Ditto for the UP Big Boys. Somewhere in one of the scrapbooks around here is a photo I took of my wife standing next to the Big Boy on exhibit in St. Louis. The best way to describe it would be a mouse standing next to a supersaurus.

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Of course the modern GP D-E locomotives crush even these goliaths.

...which was one of the reasons steam faded so quickly after World War II. The performance of EMD's FT demonstrator (introduced in 1939) exceeded the capabilities of all but the largest steam of the time. A quartet of F7s could develop more starting tractive effort than a Big Boy or an SP cab-forward—and didn't require 3-5 days of heavy maintenance each month.

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Rockies and Sierras are no joke. Running still on 150 year old right of ways and earthworks.

It's likely trains will be running on the exact same rights-of-way 150 years from now. The mountains aren't going to go anywhere.

[Dr Jefyll]

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I want a ride, too!