As we strive to make our layouts
larger and more realistic in representation of the prototypes we see,
remember or imagine - a number of techniques and schemes are utilized.
Smiles were introduced in the late 50's as a means of providing scale speeds and distances to our layouts. The use of switch lists, way bills, and other control forms provide prototypical operations and a sense of purpose to our trains.
Adherence to a specific prototype,
its details and surroundings impart a feeling of "correctness" and sets the
stage for both the trains and their operational behavior. So too, we look to
impart more prototypical modeling in the use of lighter rail size, thinner
wheel contours, larger frogs and radius curves and functionally scale
couplers in our quest for realism and operation.
Helpers are employed in simulated
and real grade situations. Multi-unit consists are used to haul unit trains
and fast freight loads. Conversely, a small switcher handles a few car task
on the local. In fact, only a single car behind a Doodlebug is common even
though the engine could (in our model version) easily haul 10 cars or more.
As each train is made up and blocked in a yard the appropriate motive power is matched by the tonnage and grade requirements of the terrain; real or modeled. I added 2 charts to make this job easier: a conversion to 40 ton cars (as originally stipulated in the handbook) and a 100 ton chart for ease of use. Just count the number of cars in your train and determine, based on your layouts grades and track speed requirements, if the motive power selected is capable of handling the cars required.
Let's suppose for example that your layout has moderate grades of 1.5% and one mining section with a grade of 3.0% grade. When flat switching in the yard at under 10 miles per hour any size cut of cars we possibly model (over 55 cars of 100 tons each) is within the realm of the prototype's ability to move them.
But, what happens as we get out on the mainline? As speed increases and the grade increases there is a sharp decline in car hauling capacity. Our moderate grade of 1.5% allows for only three 100 ton cars or up to seven 40 ton cars at 15 miles an hour.
Allowing for partially loaded
and totally empty cars, it appears that the "short" train lengths we model
of 10-15 cars is just about right. The introduction of model grades above 2%
decreases the number of cars drastically so that very short trains (3-5
cars) or the use of helpers are required.
Steve Lynch 1999