[Trains4Ever]

Hi,

Still trying to understand train and OpenRails physics, so I was wondering if someone could explain to me what is being done to calculate the braking force of the train at a given throttle percentage and max braking force.(And other values if needed)
I am also interested in how the air brakes are calculated, and if braking is applied to all wagons, or just the engines?
So if someone could explain that to me I would appreciate that very very much!

Thank you in advance!

[darwins]

This page will help you http://www.coalstone...physics/brakes/

All wagons fitted with automatic brakes will have a brake force.

You can see the brake force exerted by each vehicle if you look at the train forces page on the extended HuD.

[Trains4Ever]

darwins, on 23 March 2018 - 12:09 PM, said:

This page will help you http://www.coalstone...physics/brakes/

All wagons fitted with automatic brakes will have a brake force.

You can see the brake force exerted by each vehicle if you look at the train forces page on the extended HuD.

Thanks, but it doesnt provide lots of details on formulas and OpenRails implementation I think.
Is there maybe a better explaination, or does someone know where the code responsible for braking is located?

[Genma Saotome]

Well, one thing to keep in mind is that when the North American railroads tweeked the brake linkages, it wasn't just lets try this... they knew exactly what force they wanted the shoes to apply to the wheels. To learn that answer they had to figure out what force was too strong (because the wheel would lock up and slide) and what was too light, leaving the brake force to be inadequate. On top of that the force level to lock up the wheels of an empty car was much less than that of a loaded car.

After doing the math and sharing the results the commonly-used answer in the (IIRC) 1920's-60's was a MaxBrakeForce() value of 60-70% of the empty car weight -- which also applied to the loaded car. I know the NYC used 70% as a standard. I've seen other railroad documentation showing 60% but I don't know if that was for the one class of cars or a railroad standard.

This remained a problem for open hoppers -- rather light empty cars and heavy when loaded. Somebody invented the empty-loads "switch" which dynamically changed the brake force based on how depressed the car springs were. This came into use in the late 30's.

More modern brake shoes required redo-ing the math and I do not have an answer for you for post 1960's North American equipment.

Now, it OR simply uses the value of MaxBrakeForce() as provided in the .wag, everything would be set. I do not recall at this time if that is indeed the case.

[Trains4Ever]

Genma Saotome, on 24 March 2018 - 11:43 AM, said:

Well, one thing to keep in mind is that when the North American railroads tweeked the brake linkages, it wasn't just lets try this... they knew exactly what force they wanted the shoes to apply to the wheels. To learn that answer they had to figure out what force was too strong (because the wheel would lock up and slide) and what was too light, leaving the brake force to be inadequate. On top of that the force level to lock up the wheels of an empty car was much less than that of a loaded car.

After doing the math and sharing the results the commonly-used answer in the (IIRC) 1920's-60's was a MaxBrakeForce() value of 60-70% of the empty car weight -- which also applied to the loaded car. I know the NYC used 70% as a standard. I've seen other railroad documentation showing 60% but I don't know if that was for the one class of cars or a railroad standard.

This remained a problem for open hoppers -- rather light empty cars and heavy when loaded. Somebody invented the empty-loads "switch" which dynamically changed the brake force based on how depressed the car springs were. This came into use in the late 30's.

More modern brake shoes required redo-ing the math and I do not have an answer for you for post 1960's North American equipment.

Now, it OR simply uses the value of MaxBrakeForce() as provided in the .wag, everything would be set. I do not recall at this time if that is indeed the case.

Thanks you, that clears thing up! But if only the maxforce parameter would be used, what are the other values for?

[copperpen]

Trains4Ever, on 25 March 2018 - 09:05 AM, said:

Thanks you, that clears thing up! But if only the maxforce parameter would be used, what are the other values for?

All the other parameters control how fast the system uses the air and how fast it recharges, how much air pressure is required to get maxbrakeforce, plus several other parameters that all contribute to how the total system operates including the brake controller actions.

[Genma Saotome]

One of the other brake parameter values I've edited is for the MaxReleaseRate(). What happens is a tiny value is opened and the pressurized air simply vents to the atmosphere (it sounds like a big balloon popping when the whole train does it). For a typical US or Canadian (long) train it might take all of 20 seconds to do. Almost all values I've seen so far are waaaaay too slow. I'm presently using a value of 20 for most cars and locomotives, tho for novelty sake I'll use a range of 15-25.

No idea what might be right for non-North American cars.

[Trains4Ever]

Thanks for the replies!
I understand now!

[darwins]

Quote

After doing the math and sharing the results the commonly-used answer in the (IIRC) 1920's-60's was a MaxBrakeForce() value of 60-70% of the empty car weight -- which also applied to the loaded car. I know the NYC used 70% as a standard. I've seen other railroad documentation showing 60% but I don't know if that was for the one class of cars or a railroad standard.

There is another issue in regard to air brakes. Are the brake percentages given above for a service application or an emergency application? The Westinghouse system has different pressure reductions and therefore, presumably different braking forces for each of these.

For me the question has come to light as I have been looking through reports of past railway accidents in UK. There is surprisingly little historical information about brake systems, so these are proving incredibly useful. The report of the Euston accident in 1924 and that of the Camden accident in 1934 both involved the same type of electric multiple unit fitted with Westinghouse air brakes. However the brake percentages given are different.

The 1924 report states:

Quote

It was fitted with the Westinghouse air brake (75 lb air pressure) working blocks on all wheels; the braking power being equivalent to 115 per cent.

The 1934 report states:

Quote

Each weighed 226 tons; average brake power (Westinghouse) with air pressure assumed at 50 lbs. per square inch was approximately 75 per cent.

From this I would deduce that for service braking the brake percentage was 75% and for emergency braking the brake percentage was 115%.

The question is which one of these is the number that should be used to calculate MaxBrakeForce() for Open Rails?

[R H Steele]

Does this help any:I've got a copy of the complete abstract, but for the life of me...I cannot remember who provided or where I got it.

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[Tyler Bundy]

Hi Gerry, I sent that abstract to you at some point, but I don't remember who originally linked it in a post. I think I found it later with a basic Google search of "train air brakes" or something similar.

I've pondered a bit about why an empty car in the 1920s-60s would have a 60% empty brake ratio, while today's standards show 38%. Perhaps a combination of the increase in overall weight, plus the introduction of a new composite material for brake shoes? Maybe a different method of calculation? This discrepancy between the figures has always puzzled me, and I've seen different interpretations of the brake ratio between a number of sources. Some express the higher percentage like I've read in ancient railroad engineering books, and others cite the lower percentage figures similar the the abstract that Gerry posted.

That abstract also includes a small sample from non-new cars found in a yard. IIRC, It appears that empty cars, on average, have a higher empty percentage than the AAR recommendations, somewhere from 38-42%. They were concerned that some of these empty cars might slide with an emergency application. Conversely, the loaded cars were found to have an insufficient amount of braking effort, from 8-13% of their loaded weight.

Modern freight cars should have an empty/loaded sensor that measures how low the car sits on the trucks, but these can be easily damaged and I've seen many that were obviously not working. I don't remember a rough percentage of how many didn't work, but I do remember being fascinated to see one that was operating correctly. I'll say that most that I noticed were bent or tucked way up out of the way, in a "permanently loaded" position.

What I did realize after reading the abstract and doing a few quick calculations is that the empty and loaded brake ratio is roughly similar when the load sensor is not working correctly. IIRC, you could set up the brake physics for a car based upon a 38-42% empty ratio and the fully loaded car with the same brake force would have that 8-13% loaded brake ratio. You may want to test that theory, as it's been a few years and my memory is little fuzzy.

For years, I used Turbo Bill's Pro Pack physics for my MSTS freight cars, but I selected the brake force based upon total car weight. After reading this abstract, I think my loaded cars have too much braking power. The loaded and empty brake force should be similar, if not the same.

Tyler

[Coolhand101]

Having got back into using OR again, i have notice that the braking force from the CTN website is quite high compared to last year!

For years in MSTS and now OR, i have always use roughly the same braking weight for my EMUs and Mk1/2 coaching stock. 78-84% carriage weight 0.13cof x 9.81 with cast iron blocks.

Using the ORTSBrakeShoeFriction parameters for cast iron shoes, i could never achieved my above setup for realistic stopping distances. I had to use this friction curve to get my average 0.7g braking rate for EMUs/coaches using cast iron brake blocks:

ORTSBrakeShoeFriction ( 0.0 0.350 40 0.320 100 0.160 125 0.140 )

.

As the CTN website and testing stock now use a Cof of 0.50, i was wondering wherever to tinker with my own brake settings to allow using the original ORTSBrakeShoeFriction parameters for cast iron brake shoes.

Before i do, i just have one or two questions.

If a carriage or wagon has two brake shoes per wheel instead of one, how much percentage is there for the overall braking force?

What has change to allow using 0.50 Cof instead of the 0.20 or 0.13?


Thanks

[steamer_ctn]

Coolhand101, on 05 April 2018 - 11:31 AM, said:

If a carriage or wagon has two brake shoes per wheel instead of one, how much percentage is there for the overall braking force?

Whilst I suspect that two brakeshoes will give a better grip on the wheels, the main concern would still be the amount of braking force able to be applied to the wheel. Too much, and the wheels will skid along the track, and the train becomes uncontrollable.

Personally I don't think that it wouldn't have a major difference as far as OR is concerned, as long as the BF is not made excessive.

Coolhand101, on 05 April 2018 - 11:31 AM, said:

What has change to allow using 0.50 Cof instead of the 0.20 or 0.13?

Can you expand on your question as I am not sure what you mean.

Coolhand101, on 05 April 2018 - 11:31 AM, said:

Using the ORTSBrakeShoeFriction parameters for cast iron shoes, i could never achieved my above setup for realistic stopping distances

Do you have any real life test results for braking and stopping distances?

Thanks

[Coolhand101]

steamer_ctn, on 05 April 2018 - 06:19 PM, said:

Can you expand on your question as I am not sure what you mean.

My understanding of tread brake blocks that use cast-iron have a Cof of 0.13 and Composite brake blocks have a Cof of 0.20. Having a Cof of 0.50 results in a large number for brake force. Although the latter is on vacuum brake stock, it should be the same for air brake stock as well.

steamer_ctn, on 05 April 2018 - 06:19 PM, said:

Do you have any real life test results for braking and stopping distances?

I have a dig around on my hard drive. Most of the figures are from rail accident sites.

Basically, all tread brake coaching stock using cast iron shoes, have a average deceleration rate between 0.07%g and 0.075%g. This can range from 0.05%g at 90 mph to over 0.10%g at 2 mph. Knowing this, you can convert the data to stopping using distance as a measure. Composite shoes have an almost constant brake rate, which results in higher friction at high speeds. At 25 mph and below, cast iron shoes have greater friction and higher braking rate over composite shoes.

I haven't tried the test stock coaches as yet, but the brake force is over 130kN for a 33.5t Mk1 coach. I have always use about a 1/3 of that figure, so I'm reluctant to change all my stock for this new CoF. But I'm always improving my train sets so if this figure is indeed correct for cast-iron shoes, then i will adjust accordingly!

One other thing, Mk1 vacuum brake coaches were 5 tons heavier than Mk1 air brake coaches.

Thanks

[darwins]

Quote

One other thing, Mk1 vacuum brake coaches were 5 tons heavier than Mk1 air brake coaches.

Could you give me a data source to confirm that? I know that vacuum brake equipment is heavier than air brake equipment, and might expect this to make a difference of 1 or 2 tons.

However in the case of Mk1 coaches I would expect the air braked coaches to either be the same mass or heavier, because they were in fact dual braked.
Air brake equipment was added without the vacuum brake equipment being removed. (So in OR heavier than original or the same as dual braked using vacuum brakes.)

What did make a significant difference to Mk1 coaches were the bogies fitted.
Commonwealth bogies are a lot heavier than the original B1 bogies. I think they added 3 tons or more to the mass of the coach.
Later many were fitted with BT4 bogies which reduced the mass compared to the Commonwealth bogies and probably also compared to the original bogies.