Stopping distances

laldfordo

New member
I've been experimenting with stopping distances, before spacing the signals on a layout, by trying single, double, triple and so on heading on a standard train. I expected the stopping distance to be roughly inversely proportional to the square root of the number of engines. But it is not like that.

The rule applies for double-heading. But add more engines and there is little reduction until you have five or six together, depending I think on their length.

However, if you put pairs of engines at intervals (not too close) along the consist they do have the desired stopping power. So four engines in two pairs will stop the train in half the distance for one engine, six in about 40% of the distance and nine in a third of the distance.

I wish I'd done this experiment earlier rather than just add more engines and watch the trains still whizzing past red lights!
 
You can always go to the locos engine file and increase the " decel rate " this will stop train quicker, the higher the number the quicker it will stop. just play around with it til you get stopping distance your happy with
PJ
 
You can always go to the locos engine file and increase the " decel rate " this will stop train quicker, the higher the number the quicker it will stop. just play around with it til you get stopping distance your happy with
PJ


Sure, I do do that. But multiple-heading is an additional tool. I just wanted to let people know (those who didn't already) that multiple heading beyond double-heading is pointless as far as stopping power is concerned. Previous posts on this subject have stated that adding engines multiplies the braking power wherever you put them in the consist. But I've now discovered that is not true.
 
I don't know how these things work in the UK, but in the US, adding more locomotives does not increase the braking power, since nearly all cars have brakes on each axle (although in some cases, cars with six axles only had brakes on four). Adding locomotive units will increase the maximum speed, and the acceleration, but have little change on the stopping distance. Of more import on the stopping distance is the speed.

ns
 
Exactly, it doesn't matter how many units are on the train, the air will dump just as fast. However, if you're using dynamic brakes, more units WILL increase braking power. This is in the US though, and every axle does have a brake. More units will reduce the time it takes to charge the brakes though.
 
When you do that, do you need to jump from cab to cab to reduce the throttles on each engine or does it do that automatically for all engines?

For my experiments I was in DCC mode and all engines work together, as I am sure they do from one cab in cab mode as well.

As others say, in the real world there are train brakes, and these are simulated in Trainz. But I suspect Trainz works out the deceleration based on train mass, speed and engine max decel number (plus maybe drag) but not with any braking power on each vehicle.

That is supported by my observation that the test train with two engines stops in about 70% of the distance taken by the same train with one engine. Ie a doubling of the braking force.
 
Correction

So long since I used the equations of motion I remembered them wrongly. The distance travelled is directly proportional to the inverse of the deceleration, not to its square root.

But it does vary pretty well as the square root of the number of active engines. So the Auran algorithm, instead of just adding the braking power of additional engines, takes the square root of the aggregated decelerations.

It is the reverse of putting two things in a microwave oven at the same time. It takes not twice as long but 1.4 times as long.

Hope that helps anybody who is not totally turned off by this thread.
 
Can you really count the results that you got in DCC mode? In my experience (limited as it may be) The DCC physics are a little more simple, and all trains, stop in a shorter distance in DCC.
 
Can you really count the results that you got in DCC mode? In my experience (limited as it may be) The DCC physics are a little more simple, and all trains, stop in a shorter distance in DCC.


OK. But the point is, the results are repeatable. Two engines at the front of a train decreases the stopping distance (compared with one). Adding a third and fourth has almost no effect on the stopping distance.
 
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