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Calculating Motive Power Requirements


Nelson Moyer <ku0a@...>
 

For some reason my replies aren’t getting posted, so here is the text of the reply to Tim’s ‘rule of thumb’ method of assigning motive power to trains.

 

I found an article in the November 1978 Model Railroader on tractive effort, horsepower, grades, etc. for both prototype and model railroads. The article describes a method for scaling those forces down for practical operations on a model railroad. The conclusions are similar to yours, Tim. The ruling grade on my layout is 2% in the helix. Based upon staging track capacity, mainline freight trains are limited to a maximum of 28 cars plus ABBA F units while passenger trains are limited to 14 cars plus AA E units. The A/D track in the yard can accommodate 20 cars, so trains terminating in the yard are limited to that number.

 

Nelson Moyer

 


Tim O'Connor
 

Bill

My bad again -- I was quoting lbs-TE per ton not horsepower !!

So a loco with 22,500 lbs continuous TE on a 2% grade could lift 500 tons,
or about 10 "average" STMFC era freight cars.

The SP for example would assign five 2-10-2's to lift 50 car trains north
of Dunsmuir CA. A cab forward could take almost twice as much as a 2-10-2.
An ABBA F set could lift about twice as much as one cab forward.

On flat lands of course relative performance was very different than on
steep mountain grades.

Tim O'

At 8/14/2015 03:00 PM Friday, bill Vaughn wrote:
Rules of thumb --

5 hp/ton on 0% grade (flat land)
25 hp/ton on 1% grade
45 hp/ton on 2% grade
65 hp/ton of 3% grade

Tim I just retired off a class 1 mountain grade, I wish you had assigned us power. I have never seen anything near 25 hpt even on the hottest of trains. More like 4 to 5 hpt.

Bill Vaughn


John Larkin
 

It's been a long hot day but my math says a 110 car train of 286,000 lb hoppers would probably weigh in at 7800-7900 tons.  Given 3 units (2 front, 1 back) generating 12,000 hp, that more like 1.5 hp/ton. It's been many years (1982) but I seem to remember 4hp/ton being quite good for a hotshot running from North Platte to the Left Coast. 

John Larkin



On Friday, August 14, 2015 8:03 PM, "Tim O'Connor timboconnor@... [STMFC]" wrote:


 
Bill

My bad again -- I was quoting lbs-TE per ton not horsepower !!

So a loco with 22,500 lbs continuous TE on a 2% grade could lift 500 tons,
or about 10 "average" STMFC era freight cars.

The SP for example would assign five 2-10-2's to lift 50 car trains north
of Dunsmuir CA. A cab forward could take almost twice as much as a 2-10-2.
An ABBA F set could lift about twice as much as one cab forward.

On flat lands of course relative performance was very different than on
steep mountain grades.

Tim O'

At 8/14/2015 03:00 PM Friday, bill Vaughn wrote:
>Rules of thumb --
>
> 5 hp/ton on 0% grade (flat land)
> 25 hp/ton on 1% grade
> 45 hp/ton on 2% grade
> 65 hp/ton of 3% grade
>
>Tim I just retired off a class 1 mountain grade, I wish you had assigned us power. I have never seen anything near 25 hpt even on the hottest of trains. More like 4 to 5 hpt.
>
>Bill Vaughn