I often hear fellow modelers discuss how many cars their locos will pull or lament on how their newest ‘X’ loco doesn’t pull as many cars as they expected. Certainly in N-scale there has been a trend over the years were locos have been getting lighter (for various reasons) and don’t pull as well as their weightier predecessors.
But this leaves me wondering about something I confess I don’t have much knowledge about. While we might grumble that (for example) an N-scale SD35 won’t pull more than ten boxcars up a 2 percent grade, I have to wonder if a real SD35 be able to handle the same (assuming their fully loaded)?
I don’t know if this is asking for too simple of an answer, but is there a basic rule of thumb regarding 1:1 pulling power that can be used to compare a models performance to?
General rule of thumb is that a prototype train needs the horsepower/trailing ton of the % of grade to go up the hill.
So a 2% grade = 2 hp/tt. An SD35 is 2500 hp, so it can handle 1250 tons (2500 hp / 2 hp/tt). YMMV.
If each car was a fully loaded 100 ton cap car (130 tons gross) then an SD35 could haul about 10 cars.
Also depends on the gear ratio of the engine, the weight of the engine, the curvature of the track, what the actual steepest grade is, how fast you want it to go, etc. Prototype ratings are expressed in tons, not cars, since there is no set weight of a “car”. A car can range from about 50,000 lbs to 286,000 lbs.
Bruce,I know when I worked on the railroad the old gray beards could work the throttle and pull extra tonnage…The N&W would use 2 GP30s to pull a 200 cars coal drag.The C&O would use 3 GP9s or A-B-A to pull a 200 car coal drag between Russell Ky and Toledo,Oh.Later the same would apply to GP30s,35s 38s and GP40s.Oddly it took 3 SD35s to haul 200 cars of coal.
As far as models that depends on basic 3 things:
1.When a modeler follows RP20.1 he cuts the tractive effort of his motive power.
2.The percent of his grades…A 3-4% grade will cut a locomotives tractive power
3.Brand of locomotive.Each brand and type of locomotive come in a wide weight range from the light train set Bachman to the heavy P2K locomotives.
Also there is no real difference between metal and plastic wheel sets when it comes to roll-ability even without the use of the “tool” except for cheap train set cars with truck mounted couplers.
So,my (say)Athearn SW1500 will pull a 25 car cut whereas another guys SW1500 may only pull 12 cars…Why? Because I do not follow RP20.1 where the other guy does and thus he cut the tractive effort down on his SW1500 and now cusses his SW1500…Thats why I take dose of salt with any “complaint” I read on any forums where pulling is concerned.
You are right except… Weather can play havoc with a locomotives tractive effort be it rain to blizzard because of the rails being wet.I recall one time while working on the PRR we stalled because of ice on the rails due to a ice storm.Of course we had a SW1 and 37 cars in tow that night.
Bearing manufacturers minimize friction by achieving surface finishes who variance is measured to at least the fifth or sixth decimal place. This is state of the art technology. Assuming an N-scale manufacturer could achieve this same surface roughness in his trucks. The resulting friction force would still be 160 times the prototype because that surface roughness cannot be “scaled down”. If anything, it will be higher. Similarly, the viscosity of the lubricants may not scale down accurately either. In view of this, it is not surprising that N-scale locomotive pull as few cars as they do. Even H0 engines would have to be solid metal in order to match the pulling power of their prototype if they lack traction tires.
Bruce,I forgot the good part…These coal trains would not be weigh until they reach Portsmouth,Oh…I read about the GP30s and where these coal trains would be weigh in Ed King’s column that use to be in Trains Magazine.[tup]
Ed King was a N&W Assistant Road Foreman of Engines.