The Grantville Gazette - Volume 7 Part 35

Clearly, steam locomotion is one of the options the USE is considering. In the early days, the greatest advantage of steam locomotion was that it had a lower operating cost. For the horse-drawn trains on the B&O railroad, the "crew" was 42 horses and 12 men, and the total operating cost was $33/day. The horses towed the train at a speed of 10 mph. In contrast, the 1832 locomotive Atlantic (0-4-0, 6.5 tons), which replaced the horses, could go 20 mph, and its operating cost was just $16/day. (Dilts, 196).

(Alexander, PL4, says that it hauled 30 tons at 15 mph.) Eventually, the locomotives became powerful to pull trains too heavy for normal draft teams. As early as 1839, a Gowan & Marx (4-4-0, 11 tons, 9 tons on drivers, driving wheels 42" diameter, cylinders 12 1/8" x 18," anthracite coal burner) hauled a train of 101 loaded four-wheeled cars, weighing a total of 423 tons, from Reading to Philadelphia at average speed of 9.82 mph. (Alexander PL10).

Why not jump directly to diesel-electric (DE) propulsion? Modern locomotives use a diesel engine to power electric motors; the latter turn the wheels. DE locomotives are more fuel efficient, and less labor intensive to operate, than steam locomotives. They can exert high tractive forces at high speeds, and they can be wired so that one DE's crew can operate several at one time.

The problem is that we lack the infrastructure to support DE's. A diesel engine requires diesel fuel, and we don't have it yet. The oil fields of Germany are small, and we probably won't have a large, reliable supply of oil until we have control of the North Atlantic and can import it from the Middle East, Africa, or the Americas. In other words, we have to win the war first.

Then there is the electrical system. We will need insulated copper wire. The best insulation is rubber or plastic and, in 1632, neither rubbers nor plastics are commercially available. In OTL, the natural rubbers and plastics were obtained from non-European sources.

Finally, there is the issue of start-up costs; DE's are perhaps five times as expensive as a steam locomotive of equal horsepower. (NOCK/RE 203) * * *

Even if we recreate the steam locomotive technology, that doesn't mean that it will be suitable for all purposes. During World War One, Major Connor warned against use of steam locomotives to directly supply the front line, because a "steam locomotive would indicate too clearly its position by its smoke."

As one possible alternative, Connor provides data on Vulcan gasoline locomotives. Even the smallest can haul over 150 tons. It therefore is not so strange as it seemed at first blush that the USE is using "a modified pickup truck cab section" to draw Iona's train. Canon doesn't specify the modifications, but it probably has been equipped with locomotive-type wheels so it will run on the rails.

Gasoline locomotives were first developed for coal mines (WLW). If the Joanne mine locomotives ( Elizabeth) pa.s.sed through the Ring of Fire, they were presumably narrow gauge gasoline machines. Fuel Historically, fuel was the largest operating expense item for railroads, and the choice of fuel was based primarily on cost. The early American locomotives mostly consumed wood; it was not until 1870 that half the steamers in service were coal-burners (White 85). Fuel conversion was driven by both deforestation, and the opening of large new coal fields.

Early seventeenth-century Germany is experiencing a wood shortage because of the heavy use of wood as a fuel in home fireplaces and industrial furnaces, and as a raw material for carpentry.

On the other hand, because the Ring of Fire encompa.s.sed several up-time coal mines, and the up-time equipment for mining them, there is a readily exploitable coal supply in the Grantville area. There is also a lot of coal in Germany, notably west of Hannover, near Zwickau in Saxony, in Saarland, and in the famous Ruhr region.

So it is something of a no-brainer to prefer coal to wood. (What wood we have available for railroads is best employed in the wood-ties which support the rails.) * * *

The USE is rich in coal but impoverished in petroleum. Consequently, we cannot expect to have large supplies of either gasoline or diesel fuel within a reasonable time. Our gasoline locomotives are likely to be limited to rebuilds of up-time vehicles, and used only as a stopgap. And we aren't likely to consider building a diesel locomotive at all-at least, not until we are importing oil in large quant.i.ties.

Steam Locomotion We have completed the first stage of the engineering process: conceptual design. The princ.i.p.al motive power for the new railroad is going to be a coal-burning steam locomotive.

Both the Encyclopedia Americana and the modern Encyclopedia Britannica provide a basic cutaway view of a steam locomotive. These diagrams show, and label, certain major components of the boiler system (the firebox and its grate, the water circulation, the steam dome, and the superheater tubes), the engine system (the steam chest, the valve, and the cylinder-and-piston), the transmission system (the crosshead, main rods, and connecting rods), the driving and leading wheels, the valve control system (the eccentric crank and rod), the exhaust system (exhaust pipes, smoke box and smokestack), and the control system (throttle valve, throttle lever, safety valve). Other parts are recognizable to a railroader (e.g., the ashpan), but are not labeled.

In a steam locomotive, fuel is burnt in the firebox, evaporating water in the boiler. The resulting high-pressure steam is directed by the valve slide in the steam chest to either the front end or the back end of a cylinder containing a piston. If the steam enters the back end, it drives the piston forward and, at the completion of this forward stroke, the steam is allowed to escape. Steam then is redirected to the front end, moving the piston backward. Then the front end is exhausted, and the piston is ready for the next cycle.

This to-and-fro movement of the pistons is converted by the rods and cranks into rotary motion, each piston turning the driving wheels one half turn on each stroke of the cycle. Another linkage, driven by the rotation of the axle, controls the position of the valve slide.

The process may sound simple, but it is important not to underestimate the difficulties of building a practical steam locomotive. There are no steam locomotives in Grantville. That means that the design for the USE's first steam locomotive must be based on inspection of books and videos.

The next engineering design step is called "preliminary design" or "embodiment design." That is when engineers decide things like the size and weight of the locomotive, the fire grate size, the desired boiler pressure, the diameter of the cylinders, the piston stroke length, the number of wheels, the wheeldiameter and so forth. These in turn determine how much the locomotive can pull, how fast.

To make those decisions, we have to determine the tractive force (pull) necessary to overcome the expected train resistance to motion.

Basic Train Resistance to Motion (Straight, Level Track) The "basic" resistance on straight, level track is the result of rolling friction between wheel and rail, friction among all the mechanical parts driving the wheel (cylinder and piston, bearings and axle, etc.), air resistance, and other factors.

The starting resistance is about 20 pounds per ton of load, but the engineer can bunch up the cars and then take advantage of slack, starting the train one car at a time.

Resistance drops once the train is moving slowly. It then climbs again as train speed increases.

EB11 provides some formidable equations, of dubious relevance, for calculating resistance. I instead quote two simple historical formulae which are likely to be known to model railroaders. The resistance, measured in pounds of force per ton of load, equals

(1) 2 + (speed (mph) / 4)(the "Engineering News" formula; Ludy, 131), or

(2) 3 + (speed (mph) / 6)(the Baldwin Locomotive Company formula; Connor, 89).

Equations (1) and (2) are useful at the speeds the USE will be operating. However, for high speed modern trains, air resistance becomes important, and this introduces a factor which is proportional to the square of the speed.

Extra Train Resistance (Grades and Curves) In nineteenth-century America, poorly capitalized pioneer railroads economized on track building by taking the path of least resistance: going up and down, or around, hills. As a result, American locomotives had to be engineered to cope with steep grades and sharp curves. This could be true in the USE, too.

Total train resistance is the sum of the basic resistance mentioned above, and extra resistance attributable to grades and curves.

Grade (Slope). If it is going uphill, the locomotive has to overcome gravitational force as well as rolling friction. This grade resistance is roughly 20 pounds per ton of load, for every 1% of slope.

(Armstrong, 20) * * *

Curves force the train to reduce speed (so it doesn't derail), and also result in an effective increase in resistance. A curve with a turning radius of 5,729 feet (called a one degree curve) increases resistance by 0.8 pounds per ton of load. Halve the radius, and you double the resistance.

Rated Tractive Force EB11/R explains how to calculate the average tractive force (in pounds) exerted at the rail by the driving wheels of a two-cylinder steam locomotive engine: it is the product of the mean effective pressure (p.s.i.) of steam in the acting cylinder, the square of the piston diameter (inches), and the length (inches)of the piston stroke, divided by the diameter of the wheel. (See also Ludy, 131). The mean effective pressure at start-up is usually a.s.sumed to be 85% of the boiler pressure.

In this article, when I refer to "cylinder diameter," what I really mean is the size of the bore, which is, roughly, the piston diameter. Also, I may express the cylinder bore diameter and piston stroke length in shorthand form as, e.g., "16X24" (16 inch bore, 24 inch stroke).

The drawbar pull-which determines the load that the locomotive can haul-is its tractive force at the rail, less the resistance imparted by the locomotive itself.

The steam locomotive develops the rated tractive force made possible by its boiler and engine only if it can adhere to the track.

Maximum (Adhesion-Limited) Tractive Force The effective tractive force applied to the wheel rims cannot exceed the "adhesion," which is the product of the weight which the locomotive places on its driving wheels, and the "coefficient of adhesion."

This coefficient (Armstrong and others use 0.25; EB11/R, 0.2.) expresses how well the wheels resist sliding on the rails; higher is better. The engine can apply more force to the wheels, but they will just slip, not turn.

Consider the rail-riding pickup truck on the Grantville-Halle line. We are probably talking about a 200-300 horsepower engine, and a vehicle weight of around 5,000 pounds. At 10 mph, that engine could develop a pull of 9,000 pounds-if only the wheels didn't slip. But its maximum tractive force, thanks to the adhesion limit, is just 1,250 pounds. That means that it is way over-muscled, relative to its adhesion. Of course, "its muscles are designed for rubber tires on pavement, which have a much higher coefficient of friction." (Douglas Jones comment) Designing for Adequate Traction The desired tractive force can be calculated if we know how much tonnage the locomotive must move, over what grades and curves.

We then first ensure that the weight on the drivers is sufficient to generate adhesion at least equal to that desired tractive force. We distribute this weight across a sufficient number of axles so that the rail can handle the load.

Next, we must size the engine and boiler so that the rated tractive force is sufficient and sustainable.

A logical starting point would be to use the design parameters of an old timeline (OTL) locomotive.

EB11/R provides some useful comparative data for thirty-six different locomotives: wheel configuration, the position (inside or outside), diameter, and stroke length of the cylinders; the diameter of the driving wheels, the weights of the engine and its tender; the weight carried by the driving wheels; the grate area and total heating surface of the firebox. In fourteen cases, it also states the boiler pressure.

While EB11/R has something of a British bias, Alexander provides significant design parameters for over fifty American locos.

It should be evident from the discussion of rated tractive force that this can be increased (up to the "adhesion limit") by

1) increasing the mean effective pressure (usually by increasing the boiler pressure), 2) increasing the cylinder diameter or the piston stroke length, or 3) decreasing the driving wheel diameter

Decreasing the drive wheel diameter is the only way of increasing long-term tractive effort whichdoes not require that the boiler and firebox be enlarged to pay for it. However, it, too, has a price: reduced speed.

Large wheels are reserved for express pa.s.senger service, while small wheels are used on freight locomotives to maximize tractive effort. But the wheel diameter cannot be made too small, because it must remain larger than the piston stroke length.

For a freight locomotive, 42 inch driving wheels are typical. On a general purpose locomotive, a typical wheel diameter might be 54 inches. A little more speed, a little less tractive force. For a dedicated pa.s.senger locomotive, wheel diameter is likely to be in the 60-90 inch range, resulting in a more p.r.o.nounced tradeoff of hauling ability for speed.

If you want to increase the boiler pressure, you will have to evaporate water at a faster rate. This will require various firebox and firetube modifications. And to contain that pressure, you will have to use thicker boiler and firebox walls, which will make the locomotive heavier.

If you increase the cylinder diameter or piston stroke length, you increase the engine's steam requirements. If the boiler is mismatched to the engine, then the boiler pressure will drop, the engine will gulp for steam, and the tractive force will decline. So changes in the engine ultimately affect boiler and firebox design.

Increasing the cylinder diameter or the boiler pressure also increases the force on the piston so the piston rod must be made larger and heavier to withstand the stresses imposed by piston motion. Which in turn affects the size of the main rod, the coupling rods, the axles, and even the frames.

Making the reciprocating parts (e.g., piston) more ma.s.sive will increase shaking, which will mean more wear and tear on the engine, the running gear, the wheels and even the rail.

Increasing the stroke length necessarily increases the length of the piston rod, and hence its diameter must be increased so it doesn't buckle when compressed. The rest of the running gear then needs to be scaled up, too. With the same consequences as before.

Any mechanical engineer (there are at least ten in the Grid) will have studied, and will have textbooks describing, the basic mechanics of columns and beams, crank-and-rod mechanisms, etc. and hence will appreciate the mechanical limitations on piston rod length and cylinder diameter. It is no doubt because of the forces at work that cylinder diameters and piston strokes on locomotives rarely exceed 30 inches, even though a more ma.s.sive design would increase tractive force.

Weight and Size Because of the role of adhesion weight, lightening a locomotive is not necessarily advantageous.

Indeed, in 1835 Baldwin built the first locomotive (The Black Hawk) in which the tender was integrated into the locomotive body, so that part of its weight would contribute to the traction. (Alexander, 50).

A locomotive is likely to be designed so that the weight it places on its drivers is at least four times the desired tractive force. Of course, its boilers and engines should then be sized accordingly.

However, the basic rolling resistance of a locomotive is still proportional to its total weight. There is substantial additional resistance, again proportional to total weight, when the locomotive steams up a slope, or accelerates.

We also need to consider wheel weight. The greater the weight, the greater the wear on the rail, and the risk of rail failure.

The quality of the track is the princ.i.p.al limit on wheel load. EB11/R (847) says that a weight of 37,000 pounds "could be easily carried on one axle," and that implies 19,500 on each wheel. The heaviest rail mentioned by EB11/R is 100 pounds per yard, so a conservative rule of thumb would be toallow a wheel load of 195 pounds per pound of rail weight.

A contemporary Baldwin Locomotive Company catalogue states that if steel rails are properly supported by cross-ties, they can support a maximum wheel weight of 225 to 300 pounds for each pound per yard of rail. Thus, if a rail is dimensioned so that its weight is forty pounds per yard, no more than 12,000 pounds weight should be placed on a single wheel.

For a given weight on the drivers, wheel load can be reduced by increasing the number of driving wheels. In OTL, there was an increase in the number of coupled driving wheels.

One 1893 locomotive (Alexander PL87) had 84,000 pounds on four driver wheels, and thus the individual wheel load was 21,000 pounds (suitable for 70 pound or heavier rail). In contrast, another (plate 90) had 172,000 pounds on the drivers, but it was spread over ten wheels, and thus it could actually run on lighter track.

The wheelbase is the distance from the first driven axle to the last one. If the normal axle s.p.a.cing and wheel diameter are maintained, increasing the number of driving axles lengthens the wheelbase, which makes it more difficult for the locomotive to handle a curve. (Clarke, 122). Or turn around in a turntable or wye.

If the wheelbase is made too short, the locomotive becomes unsteady at high speeds. This was a problem with four-wheeled locomotives. (Clarke, 112-3).

There are constraints on height and width, too. The so-called "loading gauge" (the clearances provided by bridges, tunnels, road cuts, stations and neighboring track) comes into play here. In America, the rolling stock can be as wide as 10'10" and as high as 16'2." (NOCK/RE, 208-9).

The width is constrained, not only by the loading gauge, but also by the track gauge (the distance between the inside edges of the rails), as a large vehicle on a narrow gauge track may tip over when running a curve. The standard American track gauge is 4'8.5."

Likewise, the height not only cannot be so great as to be "clipped" by the roof of a tunnel, it cannot be disproportionate to the width, or the locomotive will topple over.

Increases in the dimensions of the locomotive will ordinarily mandate an increase in weight, too, unless a new, lighter structural material is employed. The materials presently available to the USE are wood, cast iron, wrought iron, steel, and a few other metals such as copper.

In nineteenth-century America, wood was used mostly in the cab and the tender frame, and as insulation. Copper was sometimes used for the heat exchange elements, because it conducts heat well, but it is structurally weak and thus copper tubing is thicker than the steel equivalent. Cast iron was used in cylinders, journal boxes, and valve boxes. For all other major components, the initial preference was for wrought iron, but this changed once the Bessemer process (1856) made steel affordable. By 1900, virtually the whole locomotive was made of steel. (White, 29-31).

We cannot put into a locomotive the most powerful boiler and the most powerful engine available, only those whose power is greatest within weight and size constraints. And the engine and boiler compete for the ma.s.s and volume allotted.

Making Steam: Locomotive Boiler Design The boiler is the stomach of the locomotive. It consumes fuel, air and water, and belches steam. The fuel is burnt to change chemical energy into heat energy; the air is necessary for combustion to occur, andthe water is what is heated to generate steam. It is the expansion of steam which moves the pistons, and ultimately makes the wheels go round.

Coal is shoveled onto a horizontal grate in the firebox, which receives air from the "ashpan" below, as well as, intermittently, through the firebox door.

The first fireboxes were mounted "inside" the wheel lines, and were long and narrow (grate area 17-18 square feet). Later, they were placed on top of the frame, and were wide but short (30 square feet). Long, wide fireboxes (up to 90 square feet) were made possible by relocating them behind the driving wheels. (Forney; Bruce, 36-43) The smoke puffing from the steam locomotive is photogenic, but it is also evidence that fuel is being wasted. In 1859, engineers solved this problem with two new elements, a brick arch and a deflector plate. Together, they controlled the airflow so as to improve combustion.

"Monty" should be familiar with these two firebox features.

There are two basic methods of using the released heat energy. Most railroad boilers were of the "fire tube" type, which means that the hot air rises from the coals and enters a mult.i.tude of pipes. These travel through the main section of the boiler, which holds the water. The heat brings the water to a boil, and the steam rises from the top of the water surface, ultimately collecting in the "steam dome." The fire tubes empty into the smoke box, and the smoke ultimately escapes through the smokestack. This creates a partial vacuum in the smoke box, which helps to draw in the air. EB11 "Boilers" shows two views of an express locomotive boiler (Fig. 10).

A few OTL locomotives were equipped with water tube boilers. Water is circulated in tubes through the firebox, rather than hot air through the water reservoir. Water tube boilers were much safer to operate, and potentially more economical, "but it was impossible to build efficient boilers of this type within the clearance limitations of the railway engine" (Sinclair, 691).

The most efficient boiler operation is at a relatively low rate of combustion, e.g., 30-60 pounds of coal per square foot of grate per hour, resulting in evaporation of 11-13 pounds of water per pound of coal, and a boiler efficiency of about 80%. Burning 100-180 pounds per square foot of grate per hour, we obtain only about 6-8 pounds of water per pound of coal, and the boiler efficiency is about 40-50%.