[gpz]

darwins, on 18 May 2023 - 03:35 AM, said:

This use of "brake percentage" in UK is identical to "Net Braking Ratio" NBR in use in USA.

Something I still don't fully understand about this NBR. :-) :-)

You say, the brake shoe force derived from the UK-USA NBR needs to be multiplied by the CoF to get the retardation force and the deceleration, right?

Is there such a thing as NBR for the whole train? In this case to calculate the deceleration of the whole train, you need to multiply the NBR-derived value by CoF here as well, simmetrically, right? What CoF to be used here, in case different cars consisting the train?

(In contrast, with UIC brakes it seems to be easy: the brake percentage for the cars and the train already considered the Cof in it, so there is no need to multiply with that.)

[darwins]

gpz, on 23 May 2023 - 02:17 AM, said:

Something I still don't fully understand about this NBR. :-) :-)

You say, the brake shoe force derived from the UK-USA NBR needs to be multiplied by the CoF to get the retardation force and the deceleration, right?

Is there such a thing as NBR for the whole train? In this case to calculate the deceleration of the whole train, you need to multiply the NBR-derived value by CoF here as well, simmetrically, right? What CoF to be used here, in case different cars consisting the train?

(In contrast, with UIC brakes it seems to be easy: the brake percentage for the cars and the train already considered the Cof in it, so there is no need to multiply with that.)

UK-USA NBR needs to be multiplied by the CoF (at any given speed) to get the retardation force (at any given speed).
Since the CoF varies with speed, the retardation force also varies with speed. So retardation force is not a fixed value. Hence the use of NBR which was a fixed, measureable value.
So the general rule was the bigger the NBR of the train, the shorter the stopping distance.
The use of brake efficiency for the whole train (sum of brake forces / sum of masses) was commonly used in UK from 1920s to at least 1960s.
The introduction of modern brake materials has complicated this! (Hence with vastly different brake types it no longer has any meaning to calculate this for a whole train.)

With UIC brakes, things are only (relatively) easy if you have the calibration graph.
The calibration curve was based on a train of SNCF carriages with cast iron brake shoes.
When everything had cast iron brake shoes you could relate the brake % to the brake force directly.
Because modern brake materials have different CoF to cast iron then the actual brake force is different to the theoretical one above.
The curve itself is different as there is much less variation of CoF with speed, so presumably calculation of this figure now would be based on maximum service speed.

Then in OR things seem to get even more complicated.

MaxBrakeForce ( ) when used ORTSBrakeShoeFriction ( ) behaves as you have previously described - the retardation force changes as CoF changes with speed.

MaxBrakeForce ( ) when used without any user defined CoF curve gives a constant retarding force.
This is not realistic, especially for cast iron brake shoes!
However it does have the advantage of relating directly to the UIC calculated brake percentages!
The overall braking then being acceptable for modern types of brake material with more linear CoF behaviour.

[Laci1959]

darwins, on 23 May 2023 - 03:16 AM, said:

Then in OR things seem to get even more complicated.

MaxBrakeForce ( ) when used ORTSBrakeShoeFriction ( ) behaves as you have previously described - the retardation force changes as CoF changes with speed.

MaxBrakeForce ( ) when used without any user defined CoF curve gives a constant retarding force.
This is not realistic, especially for cast iron brake shoes!
However it does have the advantage of relating directly to the UIC calculated brake percentages!
The overall braking then being acceptable for modern types of brake material with more linear CoF behaviour.

Hello.

A detailed description of this for simple users would be good. Of course, in a separate chapter for UK-US users and in a separate chapter for UIC users. Something that even users who are not experienced in programming can understand.

Sincerely, Laci1959

[gpz]

darwins, on 23 May 2023 - 03:16 AM, said:

MaxBrakeForce ( ) when used without any user defined CoF curve gives a constant retarding force.

According to the code here: https://github.com/o...rainCar.cs#L973
this is not fully precise. There is still an adjustment factor calculated by a formula that gives a multiplier 1 below 20 km/h, and reduces to about 0.3 between 20 and 100 km/h, and reduces further above.

Thank you for the NBR explanation. I understand that in UK-USA the NBR values have no meaning for the whole train, thus not comparable between one train and an other, even if the value would be equal.

[darwins]

gpz, on 24 May 2023 - 01:35 AM, said:

Thank you for the NBR explanation. I understand that in UK-USA the NBR values have no meaning for the whole train, thus not comparable between one train and an other, even if the value would be equal.

Historically comparison of brake efficiency or brake power ( aka NBR ) was very important for comparison between one train and another.
(This has only changed in modern times due to having different brake materials with different properties.)

Consider these accident reports:

1. https://www.railways...thPelaw1942.pdf

This accident involved a steam loco of 110 tons with a train of 25 "unbraked" wagons of 675 tons.
The steam brake on the loco and tender had a brake power of 47.19% at 85% boiler pressure.
The tender handbrake had a brake power of 11.4% of the mass of the tender.
The report estimates the total brake power (NBR) of the train was about 15%, with 6.6% provided by the loco and tender steam brake and the rest by wagon handbrakes that were pinned down.


2. https://www.railways...estwick1937.pdf

This accident involved a steam loco with a brake power of 31% and three vacuum braked bogie carriages with brake power of 78%, giving a total brake power (NBR) for the train of 52%.


Both date from the era when cast iron brake blocks were almost universal.
The passenger train with a brake power of 52% would be easier to stop that the goods train with a brake power of 15%!

[gpz]

But now it has been changed, so e.g. a passanger train with disc brakes and 52% NBR is easier to stop than a goods train with shoe brakes and also 52% NBR, but it is not known how much easier, if I understand well. Isn't there a more adequate value in UK-USA nowadays, that doesn't involve the CoF? Or by deploying the ETCS in the UK in more lines will solve this issue automatically by adapting the UIC brake percentage calculation method?

[darwins]

You are correct. In UK we have now moved over to using the UIC system. I don't know how this is dealt with in North America, someone perhaps can explain the NARA method of working.

[Traindude]

In a recent discussion on using Brake Cylinder pressure as a variable in *.sms files for vacuum-braked equipment that I started, there's two main issues that need to be addressed:

1. What do you do when the locomotives and rolling stock have brakes that release at different pressures (e. g.: a mix of GWR and non-GWR equipment), and
2. What do you do when a locomotive has both a vacuum automatic brake and a steam independent brake? Since a steam brake behaves just like an air brake (and an air brake and a vacuum brake behave in a reverse manner from each other in terms of how brake cylinders behave during application and release), how do you prevent the brake squeal from sounding, for example, as if the brakes are applied super hard when both the vacuum and steam brakes are fully released?

Just thought you ought to know.

In the thread, copperpen suggested the addition of a manual-release valve for vacuum-braked rolling stock that allows a loco with a lower release pressure to haul stock with a higher release pressure.

PS: It'd also be nice for us to have a "Centimeters of Mercury"--"cmHg" as a unit of measurement for cab gauges, as I know there are many countries in metric-system territory (before the UK converted from Imperial to Metric, of course) that used vacuum brakes as well.

[Laci1959]

Hello.

I think it should be possible to list several brake types in the BrakeSystemType ( ) entry. For example:
ORTSBrakeSystemType ( Air_single_pipe, SME ).
If applicable, supplemented by one
ORTSOrdinal ( 1 )
supplemented by an entry. If the two types are equivalent, there is no need to specify the order. This should also be used for braking the carriage of steam locomotives. I think multi-section locomotives also have such a brake.
Of course, the brake tokens must also be supplemented as follows:
EngineBrakesControllerSMEOnlyStart
EngineBrakesControllerSMEFullServiceStart
EngineBrakesControllerSMEHoldStart
EngineBrakesControllerSMEReleaseStart
If a towed vehicle has both brake systems, the train driver chooses which brake to use. If ORTSOrdinal ( 1 ) is switched on, the first brake will be the effective brake in case of parallel operation.
Instead of SME, there can be an entry for the vacuum brake.

Sincerely, Laci1959

[darwins]

Traindude, on 26 May 2023 - 01:25 PM, said:

In a recent discussion on using Brake Cylinder pressure as a variable in *.sms files for vacuum-braked equipment that I started, there's two main issues that need to be addressed:

1. What do you do when the locomotives and rolling stock have brakes that release at different pressures (e. g.: a mix of GWR and non-GWR equipment), and
2. What do you do when a locomotive has both a vacuum automatic brake and a steam independent brake? Since a steam brake behaves just like an air brake (and an air brake and a vacuum brake behave in a reverse manner from each other in terms of how brake cylinders behave during application and release), how do you prevent the brake squeal from sounding, for example, as if the brakes are applied super hard when both the vacuum and steam brakes are fully released?

Just thought you ought to know.

In the thread, copperpen suggested the addition of a manual-release valve for vacuum-braked rolling stock that allows a loco with a lower release pressure to haul stock with a higher release pressure.

PS: It'd also be nice for us to have a "Centimeters of Mercury"--"cmHg" as a unit of measurement for cab gauges, as I know there are many countries in metric-system territory (before the UK converted from Imperial to Metric, of course) that used vacuum brakes as well.

1. The locomotive should set the standard for all the rolling stock.

Not sure how this works with regard to sounds, but if loco has 25in Hg vacuum then same applies to all wagons behind it. They should all behave the same way in sound terms.

Similarly a loco using 21in Hg should cause all the stock to work in the same way.

The exception to this as Copperpen has pointed out is when a loco working at 21 inHg is coupled to a train previously hauled by a loco working at 25 inHg then it will be unable to release the brakes on the train. To overcome this then you need to let some air into the auxiliary reservoirs on each car to reduct the vacuum inside them. This is done using the vacuum release valve - which as Paul has pointed out should be the bleed off valve on the F9 menu in OR.

cmHg was used in Norway, Sweden, Austria-Hungary, Spain, Portugal and on vacuum braked lines in France, Switzerland and Germany. IIRC they used a different metric unit in Denmark!