Drawbar-pull measurements in CTT

[lionelsoni]

QUOTE: Almost any locomotive on almost any track, model or prototype,...will have a drawbar pull of somewhere near 1/4 its weight on drivers.

[Anonymous]

now....

ounce for ounce, how much weight does the prototype pull compared to some of our common toy models?

[Anonymous]

Daan:

Some conversion factors for you:

16 oz = 1 pound
The weight of 1 Kilogram = 2.2 pounds

If that wasn't crazy enough for you:

1 inch = 2.54 centimeters
1 foot = 12 inches
1 Yard = 3 feet
1 Fathom = 6 feet
1 Mile = 5,280 feet
1 League = 3 Miles

Tony

[lionelsoni]

An ounce, when used as a unit of mass, is about 28 grams. When used as a unit of force, it is about 278 millinewtons. One of the few advantages of our non-metric system is that the weight of an object in pounds of force (or ounces of force) is equal to its mass in pounds of mass (or ounces of mass). This is particularly handy in train calculations, where the force (in pounds) needed to pull a train up a grade is the mass of the train (in pounds) divided by the slope (in rise over run).

In the case of this little locomotive, the force that CTT says they measured is 1/1000 of the locomotive weight. From this, I calculate the maximum grade as 1/1000, or .1 percent, or 1/8 inch in 10 feet, or 1 mm in 1 m. This is of course absurdly low and obviously wrong.

Almost any locomotive on almost any track, model or prototype, without any traction aids (like rubber tires or Magnetraction), will have a drawbar pull of somewhere near 1/4 its weight on drivers. An example of this is the previous locomotive reviewed in the same issue, a Hudson, which is said to weigh 200 ounces and have a drawbar pull of 55 ounces. Thus the switcher, at 20 ounces, should have a pull of about 5 ounces. It is possible that only one of its two axles is powered (although Bob didn't mention this), which would lower the pull to around 2.5 ounces. But this is still over 100 times what CTT reported.

[daan]

I have read that too, and automaticly assumed that it was 0.2 ounces instead of .02, like it was a typing fault. I prefer to talk about Newtons pulling power, because it is a force other than gravity (a tiny force in case of that switcher). But I'm a bit odd sometimes. In this case it would be 0,2N which is less than the average N-gauge lokomotive. (I presume that 1 of "your" ounces is 100 of grams. and 100 grams is roughly 1 newton).
But I'm probably too theoretical...[:o)]

[Anonymous]

i wonder if maybe they should do it like they do at them loud, muddy tractor pulls.

build a sled with a weight that climbs the sled, increasing it's friction as it moves and measure the distance when it finally cant pull no more!
[:D][:I][}:)][:O][:P][:)][:-,][:-^][:D][:D]

[lionelsoni]

I have the same kind of gauges, Dave, which I trust not to give wildly inaccurate readings. I can't say that I have the same confidence in CTT's electronic gauge, however, despite (or because of) being in the electronics business myself.

[FJ and G]

I've got a small gauge with a hook on the end that I use for drawbar pull. I don't have measurements with me; in fact, I didn't even jot them down. I used to use it for ergonomics experiments when I was a Human Factors Engineer professor at the University of Arkansas.

Dave Vergun

[lionelsoni]

I just noticed, rereading this year's March issue, that Bob Keller reported in a review that a certain 20-ounce switcher had a drawbar pull of .02 ounce! He did acknowledge that this was "tiny". Bob, did you notice that so little pull would mean that this engine could not climb a grade of 1/8 inch in 10 feet!

I generally disbelieve CTT's locomotive measurements, particularly after the postwar-GG1 article in 1998; but this is a new extreme!