Here I go again.....

Re: Here I go again.....

Postby j p » Sat Jan 11, 2014 5:35 am

I don't run my trains too fast :)
There is no need for superelevation at the speed I am using. But it looks good! It requires some experimenting to be sure that the train would be stable also when it stops in the curve. Model train is not a roller coaster.

Check this from 8:30
http://www.youtube.com/watch?v=3PmhwPceV0k
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Re: Here I go again.....

Postby LVG1 » Sat Jan 11, 2014 1:30 pm

ConducTTor wrote:This is very interesting. I *thought* superelevation would help the cars around the curve.


Superelevation helps at high speeds. But for long and heavy trains it's a thread—especially when accelerating or running uphill.

That's why it's hard for engineers to construct railroad lines which shall be used for both high-speed and freight traffic. And it becomes even harder and eventually impossible the higher the requested speed and the more complex the terrain.
An example: In the 1940s and 1950s, many North American railroads superelevated the curves of their mainlines to speed up their passenger trains. But after the foundation of Amtrak, they reduced or even eliminated these superelevations to make their lines more suitable for freight traffic again.

j p wrote:You'd be surprised, but the laws of physics apply also to the model train.


That's absolutely correct.
That's why I wonder why nobody has asked yet why model trains can run non-prototypically fast through non-prototypically tight curves and why model trains so seldom tilt to the inside of a curve.
The reason is the differences in the conditions. Model trains are usually clearly shorter than prototype trains. Additionally most model vehicles—especially fully laden freight cars—have a clearly lower center of mass. And model trains do not contain loads which change their position like partially filled tank cars which rises the affinity to tilting.

But there are further points—the height of the couplers, for instance.
The couplers are the working points of the force making a vehicle tilt to the inside of a curve. The lower the coupler, the higher the force necessary to make a car tilt. Theoretically, it will be impossible to make a car tilt if the coupler is below rail top level. :wink: :whistle:
That's why all new coupler systems for model railroads developed within the recent decades in Europe are lower than their predecessors.

And don't forget the flanges! With prototypical flanges under normal circumstances, the force necessary to push or pull the flange over the rail top is lower than the force necessary to make a vehicle tilt. With large flanges, the ratio is contrary. But the force necessary to make a car tilt doesn't change. So large flanges are for save running. And that's why NEM recommend to use large flanges and most European manufacturers keep to that.

To make a long story short:
The longer your trains, the higher your couplers, the smaller your flanges and the steeper your grades, the more problems will be waiting for you in tight curves.
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Re: Here I go again.....

Postby Juup » Sat Jan 11, 2014 5:59 pm

This thread is becoming a small goldmine for useful information. Latest nugget for me was ConducTTors point about the challenge of having high speed passenger and goods trains travelling on the same line and how this impacts on superelevation. Super thread.

I am seeing three perspectives here:

1. The physics of the prototype.
2. The physics of model trains.
3. The quest for a sense of realism in our modelling.

Obviously, 1 and 2 are different but perhaps not entirely so. We bridge the difference with 3 :)

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Re: Here I go again.....

Postby ConducTTor » Sat Jan 11, 2014 7:08 pm

On my show layout I have some super elevation (very slight). I'll have to do some testing with various trains and see if there are any bad side effects - so far there have been zero problems. I love the way super elevation looks.


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Re: Here I go again.....

Postby j p » Sat Jan 11, 2014 9:30 pm

LVG1 wrote:
And don't forget the flanges! With prototypical flanges under normal circumstances, the force necessary to push or pull the flange over the rail top is lower than the force necessary to make a vehicle tilt. With large flanges, the ratio is contrary. But the force necessary to make a car tilt doesn't change. So large flanges are for save running. And that's why NEM recommend to use large flanges and most European manufacturers keep to that.


When I look at the NEM standard, I cannot agree with your last sentence.
NEM does not recommend to use large flanges. NEM defines a range for the flanges. Most European manufacturers use the largest flanges allowed by NEM. It would run safe on finer flanges (such as RP25). Large flanges are for toy-train operation. The manufacturers want to sell, so they are trying to cover model railroad as well as a toytrain on the carpet in the living room.
Fortunately, it is always possible to turn the flanges to a more acceptable size if needed.
The flange height D according NEM310 is min 0.5 mm and max 1 mm, but NEM recommends actually the 0.5 mm, not 1.0 mm.
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Re: Here I go again.....

Postby krokodil » Sun Jan 12, 2014 3:15 am

ConducTTor wrote:On my show layout I have some super elevation (very slight). I'll have to do some testing with various trains and see if there are any bad side effects - so far there have been zero problems. I love the way super elevation looks.


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Fortunately in our scale a very little superelevation (<0.8 mm) shows already big effect, what is within the tolerances of our model trains, designed partially also as toys. :grin: :smile: :grin:
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Re: Here I go again.....

Postby LVG1 » Sun Jan 12, 2014 10:39 am

j p wrote:When I look at the NEM standard, I cannot agree with your last sentence.
NEM does not recommend to use large flanges. ...
...
"1) Das Anstreben dieser Werte führt zur größtmöglichen Vorbildnähe. "


I used the word "large" to describe a contrast to "prototypical". I didn't mean it as differentiation between various larger-than-prototypical measures.

By the way:
You should check your example.
The sentence "Das Anstreben dieser Werte führt zur größtmöglichen Vorbildnähe." (The aspiring to these values leads to the largest possible prototypicality.) is not a recommendation. It's a pure statement without any assessment.
You should rather have a look at the sentence: "Die Maße weichen von den maßstäblichen Verkleinerungen des Vorbildes im Interesse der Betriebssicherheit ab." (The dimensions differ from the downsizing to scale for concerns of operating safety.) (NEM 310, edition 2009, sentence 3)
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