Locomotive's Optimum Weight

[WGL]

  There is a formula for calculating the optimum weight of rolling stock, at least partly because ready-to-roll ones are not always made heavy enough.  Do the manufacturers of locomotives determine the optimum weight & make them in accordance with it?  If that is not always the case, is there is a way to calculate the optimum weight of a specific locomotive, or are there too many variables?

[Yampa Bob]

Too many variables. Remember that a locomotive also has to pull it's own weight. Most locomotives will be of sufficient weight out of the box for operation on level track.

I would consider "optimum weight" to be the weight that allows good pulling performance for your particular needs or wants, while not preventing the drivers from spinning when stalled.

[Jim Banner]

Most manufacturers design their locomotives to slip their wheels before the motor current gets so high that the motor burns out.  If you add more weight, you run a real risk on having your motor burn out because you have, in effect, tied down the safety valve.

In large scale, I run some locomotives with extra weights and a much higher than normal motor current.  This would cause certain failure except for the fans I install to force ventilate the motors (much like the real railroads do on their diesel traction motors.)  As yet, I haven't figured out how to do this in H0, particularly in steam locomotives where the motors tend to be small and poorly ventilated.

[Yampa Bob]

Consider a 200 ton locomotive. If you scale the weight down to HO, that equates to 9.7 ounces, much too light for good pulling.  Doubling that to 18 ounces is probably more realistic.  All my GP 35 & 40 weigh about 15 ounces.

I have never found the need to add weight to any of my locomotives. Even my tiny GE 44 ton will pull 15 cars at a good 50 mph speed, yet it only weighs 5 ounces. Of course my track is level, if I had grades I would simply add a helper.  I have several powered cars that can be added to the mix if needed, a DCC powered caboose being my favorite.

[mf5117]

so it it bad practice to fill your hoppers .and create your own loads for different rolling stock . i plan to have an area of about a 2" rise on the backside of my layout  then down. not tunnel height .

regards mf

[Yampa Bob]

Not at all, adding scale looking loads adds to the realism.  For real railroads, the overall ratio of rolling resistance is less for a loaded car than for an empty car on level track. I haven't as yet figured out a way to measure required pulling force of a car moving at 50 mph.

[mf5117]

i had heard that .125 / .190 per 1'-0 is rule of thumb , for ho. so on the 22" rad on the outside loop . i may have to lower my grade to be 2 to 3 % . im adding a 3" to get the full prim of the 4x8

[WGL]

  Don't steam locomotives carry sand to release onto the rails for better traction?  I don't know exactly how they do that.  Since we can't put sand on our tracks, maybe traction tires are the alternative.   

Not at all, adding scale looking loads adds to the realism.  For real railroads, the rolling resistance is less for a loaded car than for an empty car on level track.

  Bob, that's interesting about rolling resistance.  I do like my freight cars to carry scale loads:  Ballast iron ore, tiny wooden crates (I cut from craft dowels), cattle for my cattle car, scrap metal, logs, barrels, & etc..

[pdlethbridge]

Bob, its very interesting that the scale weight of a loco less than the actual weight of our locos. But if we were to scale down the weight of cars, they would weigh an ounce or 2. A lighter loco to pull a lighter load. Unfortunately, they would not track well because of their light weight. I too, like to run cars with prototype loads. I have a car for tea and another one for donuts!

[Eryalen]

Bob, its very interesting that the scale weight of a loco less than the actual weight of our locos. But if we were to scale down the weight of cars, they would weigh an ounce or 2. A lighter loco to pull a lighter load. Unfortunately, they would not track well because of their light weight. I too, like to run cars with prototype loads. I have a car for tea and another one for donuts!

They must be awfully small donuts.

[SteamGene]

Both steam and diesel locomotives use sand for traction - electric, too, I imagine. If you look at the top of a steam locomotive you will see one or more domes with one or more hatches in them.  Usually there will be piping running down the boiler side.  The dome or domes are the sand domes and the pipes are the delivery system to the wheels.  The engineer controls the amount of sand delivered to the drivers.  With diesels, all this is hidden. 
Gene

[WGL]

  Thanks, Gene, for explaining how the sand is applied.  I've never seen sanding in action.

[Stephen D. Richards]

Sanding....of course the rail yards are not as they once were, but if you get the chance to visit a rail yard somewhere, check on the ground for little (or large sometimes) piles of sand along the rails.  Until a few years ago I never knew what that was about.  That is from the sanding actions of the locomotives.  If you see a big pile, the engineer forgot to turn of the sand!  lol      Stephen

[rogertra]

The optimal weight for a model locomotive, without traction tires, is to cram as much weight as you can into the body shell, keeping the weight balanced around the centre of the driving wheels on steam, so that the loco can still spin it's drivers under full throttle.

If the loco cannot spin it's drivers under full throttle, then you risk motor burnout so remove some weight.  Traction tire fans, please note that little tit-bit.

[ta152h0]

casings and frame made out of depleted uranium ( black hole stuff ). but it would be tough to isolate all elements of DCC system.