The purpose of NMRA RP 20.1 Car Weights, is keeping trains on the track, not scaling model weight to match prototype weight. It is well known that a light car inbetween heavier cars can get pulled off the track on curves (stringlining). The solution is to weight all the cars about the same. At the time RP-20.1 was published models contained a good deal of die cast metal and were in general, heavier than modern molded plastic models. It being easier to weight up light cars than to lighten heavy cars, the standard was set a bit heavier than it might otherwise have been. And since model rolling stock lasts a long time (I run some cars that are 50 years old) nobody wants to change the standard.
David Starr www.newsnorthwoods.blogspot.com
OK I know the NMRA has their reccomended weights for various rolling stock, I have heard more than a few times that model ocos are able to pull more cars than their protortype. I'm looking to do a thought experiment on what would give more accurate "trailing tonnage" for our models.
Mind you I'm not looking to turn the reccomended practice on its head, it works well and for most modelers its just fine. But I feel that the RP may be out of date considering the quality of models today vs from the 50's and 60's.
Lets be honest, the typical diesel loco in those days had a single powered truck. Many steam models had the drive in the tender. Most were very lightly weighted. All add up to poor pulling power.
Todays diesels are pretty much all wheel drive and tender drive steam is pretty much non existant. Newer locos simply ahve more pulling power than they used to.
Im curious as to how prototype loco weights compare to prottype trailing tonnage and how that can be "scaled down" to modeling. I know theres been many discussions on how weight doesn't scale very well, and I belive there will never be an acceptable answer to that question. So i'm thinking of more proportional weights.
I think and example of what I'm thinking would give the clearest explanation, so:
lets say a 4 axle diesel weighs 150 tons, and can pull a trailing tonnage of 1500 tons. Thats 10 to 1.
Lets say a HO model of that loco weighs 15 ounces, how close to 150 ounces of trailing tonnage does it pull? Are we still close to 10 to1?
The flip side to this becomes car weights, so a loaded 50 ton hopper weighs 50 tons. If the loco math stays the same (10 tons equals 1 ounce) then a loaded model should weigh 5 ounces.
And of course the flip side to loaded cars is empties. What does an empty 50 ton hopper weigh? What should its model weigh?
While the weights of locos (prototype and model) are pretty easily found on the internet, finding good trailing tonnage numbers is a bit more difficult. Obviously those numbers have a huge number of variables in the real world due to grades, curves etc etc etc, but someone somewhere should have some knowledge of what a given loco could pull on a given railroad. I'm thinking A former UP or SF employee caould share some info for a long flat fairly straight division of one of them.
Of course a thought experiment is a fun bag of what ifs and why nots, putting it into practice would be quite enlightening and entertaining. This could add a whole nother world of challenges for the operations type modelers (train handling changes for the engineers, blocking cars for the yard crews, the dispatcher now has to take train weight into consideration when deciding which to put in the hole etc etc)
Modeling the Cleveland and Pittsburgh during the PennCentral era starting on the Cleveland lakefront and ending in Mingo junction