Canadian Mountain Passes Rolling Stock Physics

[mrgreen]

I'm really excited about this new route from Milepost Simulations and DTG, especially the updated and more realistic physics of the locomotives and cars included in the DLC.

There are however some things I think could use some modification.

I have compared some of the physics of the rolling stock with Run8, seeing as Run8 is arguably the most realistic commercial simulator when it comes to NA freight trains.
I wanted to post my findings here before I mail RSC with my suggestions. I think you will be surprised by some of the numbers.

Seeing as most of the trains in the scenarios in CMP (Canadian Mountain Passes) are 80 cars or less I decided to compare some timings with a train of equal length (80cars/5000ft) in Run8.
All the TS2014 timings are with realism mode set at Hard (4#)

Brake application time at full service (the time it takes for the whole train to reach full brake cylinder pressure)
Run8: 1m25s
CMP: 1m45s

Brake release time: (the time it takes for the brake cylinders to fully release on the whole train)
Run8: 5s
CMP: 10s

Brake Pipe Recharge Time (the time it takes for the brake pipe to recharge from 64psi to 90psi on the whole train)
Run8: 7m
CMP: 4m30s

I noticed that the Brake Pipe pressure falls to 65psi and the Brake Cylinder pressure reaches 58psi in CMP at Full Service. According to this website: http://www.railway-technical.com/brake2.shtml it should be 64psi on both.
Maybe there are variations from train to train?

All in all the timings are pretty similar so I think DTG has done a pretty good job. Unfortunately there seem to be some bugs when it comes to the scripting of the air brakes.
If you set the brakes to full service the performance will be close to that of Run8 but obviously you rarely use full service in normal conditions so I decided to compare the time it takes for the brakes to apply with a 10lb reduction.

In Run 8 the time it takes for a 10psi reduction is almost linearly proportionate to that of the full service reduction (i.e. a 10psi reduction takes about 38% of the time compared to a full service reduction) but in CMP the time the Brake pipe takes to reach 80psi is almost the same as that of the full service application!

I found that you can "cheat" this by dropping the brakes lower than what you want and then when the BP is about to reach your intended target you raise the Equalizer Reservoir pressure back to 80psi (or whatever you intended).
Obviously this isn't very realistic so I hope DTG can fix this so that the time it takes for the brakes to apply proportionate to how big the reduction is.

I also went in to the .bin files to check the brake force values of the locomotives and the freight cars.
The ES44AC has a brake force value of 61% of its weight in kN, the cars have have 55% and end up with about 13% when loaded. I have read on this forum before that 13%, when loaded, is realistic.

The "proof" for this was found in this document: http://books.google.se/books?id=8y3_xqbY0gYC&pg=PA124&lpg=PA124&dq=freight+car+brake+force&source=bl&ots=vFxzfsuNfg&sig=ManUCpUAXImRu9oa-Rh5HnZu6vw&hl=en&sa=X&ei=6MQAU66bCsfnywPUuIGoDA&ved=0CFAQ6AEwBg#v=onepage&q=freight%20car%20brake%20force&f=false on page 125.

Reading some discussions about freight train stopping distances, however, made me doubtful of this low number.

For example it is said that it can take a long freight train traveling at 55mph a mile to stop.
Lets say a freight train dumps the air at 55mph; with 13% brake force and a highly unrealistic 0 second brake propagation time it would take that train 1.4miles to stop.

Reading this website: http://www.trainorders.com/discussion/read.php?1,124516 where one engineer said that taking the square of the speed would give a reasonably good estimate, in feet, on level track, made me even more doubtful.

I decided to try it out in Run8.

I set the brakes to full service and timed the deceleration when the brakes had fully applied and the number I got was quite a bit higher than 0.13m/s^2 (even when taking in consideration that the locomotives would up that number a bit).
0.5m/s^2 was the average deceleration.

I decided to reread my second link and found that (I think) it was a simple confusion of units that came to the 13% conclusion. In the document it states that the minimum Net Braking Ratio required for cars equipped with COBRA shoes is 6.5% and the maximum is 10%. With 6.5% Net Braking Ratio on a 263000lbs car this would give a brake force of 17095, but in pounds of force.

If I am in fact correct and the brake force of the car is in pounds of force, you have to multiply it by the force of gravity. So 17095*9.81 = 167701. Then take that number and divide it by the weight of the car (263000lbs) and you get a deceleration rate of ~ 0.63m/s^2 or in Railworks terms: Maxforcepercentbyvehicleweight >63<.

So now you might ask, if 0.63m/s^2 is the absolute minimum required brake rate, how come the train in Run8 only had a deceleration rate of 0.5m/s^2? Well, I actually found out (by mistake) that in an emergency application the brake cylinder pressure is increased compared to full service. At least that is the case in Run8. If this is prototypical, it explains why the full service application deceleration was slightly slower than that.

There is a lot of math for me to mess up so this last part might be completely incorrect, but it is the only way for me to explain the brake performance in Run8, the "rule of thumb" equation from the engineer, and the stated braking distance (by operation life saver).

TL;DR:

I suggest DTG that modifies the scripting:

1. So that the time to apply the brakes to full service is reduced by 20 seconds.

2. So that the time it takes to release the brakes is reduced by 5 seconds (or leave it as it is since 5 seconds is such a small difference).

3. So that the time it takes for the brake pipe to recharge after a full service application is increased by 2.5 minutes.

4. So that the time it takes for the brakes to apply on lesser applications is proportionate to their size compared to a full service application.

5. So that (Maybe) the brakes on loaded car gives a full service deceleration rate of about 0.5m/s^2, or an emergency deceleration rate of at least 0.63m/s^2; either by making two separate cars (one empty, one loaded) or by increasing the brake force to 200-260% (yikes!)

EDIT: DTG should also modify the couplers so that they have the same SpringCoefficient and Damping as the couplers that come with the rolling stock from Marias Pass (15000 & 12000).

I live in Europe so all this is pretty theoretical, and foreign, to me; so hopefully the more knowledgeable people on here can correct me if I'm wrong.

Thanks in advance

[buzz456]

Since this is highly technical I am going to move this.

[dfcfu342]

I believe I read somewhere before that the recharge rate rate for the break pipe is a constant value and so if you increased it to take the full 2 and half minutes it would take that time whether you had 1 car or a 1,000. DoveTail is pretty limited based on the game engine they inherited from Kuju and so most of the breaking mods people ask for, specifically timings, just aren't really possible without a rewrite of of the game engine and good luck wishing on that one