Tractive pulling power

[mickeykelley]

Just as a curiosity, has anyone ever tested the tractive power of the various Spectrum units, the 2/3 truck Shay, Climax, 2-6-6-2, Heisler, K-27 and C-19?  The. Compared that to real world specs?  Just curious.

[Kevin Strong]

Drawbar pull is usually measured for the reviews in Garden Railways magazine. They use a rough estimate of 1.25 ounces of drawbar pull per car, so a locomotive with a drawbar pull measured at 2 pounds would be (by their estimates) able to pull 26 cars on straight and level track.

A quick survey of some of the Bachmann locos based on GR reviews:

C-19 - 2 pounds = 26 cars
K-27 - 2.5 pounds = 32 cars
2-truck Shay - 2.5 pounds = 32 cars
2-6-6-2 - 2.5 pounds = 32 cars
Climax (early version) - 1.1 pounds = 13 cars
4-4-0 - 1.4 pounds = 17 cars
2-6-0 - 1.4 pounds = 17 cars
0-4-0 - 1 pound = 12 cars


Now, about translating that to the "real world?" We need to consider a few things, but first and foremost is the weight of the average cars being pulled and the grades being climbed.

Here's a link to the 1885 Baldwin catalog, which has photos and builder's data for many narrow gauge locos.
https://archive.org/details/illustratednarro00baldrich

Consider the Baldwin 8-18D, which is the Bachmann "centennial" mogul. (The fancy one in the pretty colors.) On the flat and level, the loco is rated at 895 tons. On a 3% grade, that drops to 70 tons.

The 10-26E is the C-19. On the flat and level, it's rated at 1630 tons. Get that same loco on a 3%, and it drops to 130 tons.

Note also that the introduction of just a half of a percent of grade reduces the tonnage by over half.

That's the numbers, so how does that translate into cars? That depends on the weight of the car. Early freight cars (c. 1870 - 1900s) were low capacity, so maybe 10 - 20 tons each fully loaded. Later cars could weigh upwards of 40 tons each.

Let's look at the C-19, then, and take an average car weight of 25 tons (the capacity of a D&RGW box car).

"By the book"

Flat - 1630 tons = 65 cars
0.5% - 655 tons = 26 cars
1.0% - 395 tons = 15 cars
1.5% - 275 tons = 11 cars
2.0% - 205 tons = 8 cars
2.5% - 160 tons = 6 cars
3.0% - 130 tons = 5 cars

Here's the mogul:

Flat - 895 tons = 35 cars
0.5% - 335 tons = 13 cars
1.0% - 215 tons = 8 cars
1.5% - 150 tons = 6 cars
2.0% - 110 tons = 4 cars
2.5% - 85 tons = 3 cars
3.0% - 70 tons = 2 cars

When you compare the numbers for the prototype compared to the models, the prototypes can outpull the models on the flat and level (based on GR's estimates), but with the introduction of even half of a percent grade, the models can outpull the prototypes. Consider also that the model locos are all "geared locos," so they are not nearly as affected by grades as the prototypes. A model loco that can pull 15 cars on the straight and level can handle half that up a 3%.

So, the question for the modeler is whether we tailor our trains to reflect how the prototype would respond to those grades, or whether we just want "typical" trains regardless of the terrain on our railroads. Two car trains may look ridiculous, but they may be prototypical.

Later,

K

[mickeykelley]

Thanks Kevin.  That was very informative and really kind of what I was interested in.

[the Bach-man]

Kev!
What a great analysis!
Thanks a lot!
Best,
the Bach-man

[mudhen]

Read your information and find it to be right on as per running my K-27's and C-19 on my outdoor railway.
With my grades I can usually run with 2 to 5 cars including caboose max.
You made me fell better about my engines tractive pulling power. They in my opinion on my layout are
running prototypically. I originally thought the engines where way under powered.