[Stijn D.C.]

Hello,

On trains you have some text like this:

P: 73t

G: 61t

R: 94t


For engineering i use value of "p", but i must know of this is good way for give the right MaxBrakeForce ( 73kN )


In advance thanks,

Stijn

[ErickC]

Just multiply the car weight by the correct braking ratio. AAR standards are here.

I'd imagine that since AAR-compliant components are in service all around the world, you probably won't end up too far off.

[Genma Saotome]

ErickC, on 21 January 2019 - 01:53 AM, said:

Just multiply the car weight by the correct braking ratio. AAR standards are here.

For modern brake shoes.

Go back 50 years and instead of 38% of empty car weight you'd find (in North America) it was 60-70% with each railroad setting their own standard percentage. Apparently modern shoes grab the rim so much better than the old types they don't need as much force applied.

Which leads me to wonder... assume we have two cars from each era that weigh the same. if you use 38% and I use 70% what does OR do to produce what should be am identical braking effect?

[ErickC]

Bear in mind that all the sim wants is the total retarding force, and that the brake ratio will give us that. Also remember that the leverage ratio between the cylinder and shoe is different between cast iron and composition shoes, so the end result should be more or less the same in terms of nominal retarding force.

What would be nice, though, is if OR modelled the difference in overall behaviour. From what I've read, cast iron shoes are pretty worthless at high speeds but a little too effective at low speeds, whereas composition shoes are great at high speed but lose effectiveness at low speed.

You are correct that the numbers for unloaded care may not be correct depending on the era. Empty/load switches were not always a thing. In that case, you would use the loaded ratio, and remember that 25% is about as much adhesion as the shoe can possibly get on the wheel (much as with the wheel and rail).

[Genma Saotome]

Do you know of any examples of ORTSBrakeShoeFriction() for cast iron shoes? I don't. My fleet is 100% cast iron shoes. and the only technical data I have from the era is what percentage of empty car weight the brake rigging was to be set to apply to the shoe.

[ErickC]

Ah, I missed that parameter when I was doing my homework. It seems you can model that behaviour after all... interesting.

I'll see what I can come up as far as curves go, but I doubt I'll be able to find much. "Management of Train Operations and Train Handling" quotes 33% COE for high friction composition shoes at 60 mph and 15% for low friction composition shoes (also at 60 mph).

[R H Steele]

I have not devoted much time, yet, to learning about brakes. Good thread to read, thanks for the information.
Excerpt from the manual 8.6.1 Brake Shoe Adhesion:

Quote

Advanced Adhesion SELECTED and legacy WAG les, or NO additional user friction data dened
in WAG le - OR assumes the users assigned friction coecient have been set at 20% friction
coecient for cast iron brakes, and reverse engineers the braking force, and then applies the default
friction curve as the speed varies.

There is also a sample ORTSBrakeShoeFriction curve for composition brakes among other things.

[ErickC]

Here are some curves from "Management of Train Operations and Train Handling":



Note that both curves cross at low speeds (but it's more obvious on the 4-axle example).

Here's my question: the OR manual is really unclear about what this parameter does. Does it apply a coefficient to the maximum brake force value? Or will we need to create a coefficient curve, then multiply each y value by the nominal maximum brake force value calculated by the brake ratio?

While we're on the subject of brakes - this book has all kinds of charts for application and charging times for trains of varying lengths. If someone would be willing to turn this data into something that could be more or less universally applied (I'm guessing that a "pretty accurate for most cars" set of parameters could be compiled), I'd be more than willing to scan these charts (be advised there are a lot of them).

[steamer_ctn]

ErickC, on 21 January 2019 - 09:33 PM, said:

Here's my question: the OR manual is really unclear about what this parameter does. Does it apply a coefficient to the maximum brake force value? Or will we need to create a coefficient curve, then multiply each y value by the nominal maximum brake force value calculated by the brake ratio?

This might shed some light onto your question.

[Genma Saotome]

ErickC, on 21 January 2019 - 09:33 PM, said:

If someone would be willing to turn this data into something that could be more or less universally applied (I'm guessing that a "pretty accurate for most cars" set of parameters could be compiled), I'd be more than willing to scan these charts (be advised there are a lot of them).

Highlights are mine.

Yes! I'm delighted that Peter has compiled a lot of information on the theory but I'm not (yet) at a place where I can make sense of it all and apply it to a 1940's US boxcar's .wag.

What I need is a "starter set" of parameters and values that I can drop in for now while I do my homework on the theory behind it all. The "starter set" needs to be convertible back into the parameters of the various formulas so one can go from there to calculating values for other cars.