Brake Physics

  • I don't speak German so hopefully it is okay that I post this in English.


    My knowledge regards mainly Swedish trains but since they use the same UIC system as German trains and German wagons (both passenger and freight) run through Sweden mostly without any modifications (locomotives need to install the ATC cab signalling system however), this may be of interest to developers that create German rolling stock.


    Depending on what brake type is used (G,P,R) the application and release times will be different
    Application time/Release time


    G: 15s/45s
    P&R: 3-5s/15-20s


    Unfortunately the only sources I have for these numbers are in Swedish but perhaps someone knows of official UIC sources. From my understanding these numbers are for each locomotive/wagon which means that for a long train the application/release times will increase by the time it takes for the air signal to reach the end of the train. So for a long freight train in G-brake it might take over 20 seconds to apply the brakes on the last wagon. For example, the northern Swedish Iron Ore trains with 68 wagons can take around 23 seconds to apply the brakes and maybe up to a minute to release the brakes.


    Another example: A 600 meter long freight train with wagons in P-brake will take 6 seconds for the signal to reach the end of the train and then the above mentioned 5 seconds for the brakes to apply resulting in about 11 seconds to apply brakes. The time to release the brakes would then be between 21 and 26 seconds.


    It seems like almost all freeware/payware trains I have tested have too short timings for the brakes, especially the release timings. EP-brakes will eliminate the time for the signal to arrive but not the above mentioned application times since they are a function of the air brake system in a single vehicle. Perhaps the case is different in EMU/DMUs, I'd love to hear information about these differences.


    When calculating the retardation value for a wagon/loco (the "weight"-value in the .bin-files) one cannot just take the "Bremshundertstel" = "Bremsgewicht"/"Gesamtgewicht" because this value will be too high. For historical/arbitrary reasons the real retardation value is a fraction of the BrH. I can give a full table of these values if people are interested but I don't have the file on this computer.


    Some examples: If Brh = 100 the retardation will be about 0.8m/s^2, if it is 160 it will be around 1.4m/s^2.


    One last point that is important. For some modern passenger wagons there will be 4 Bremsgewicht values painted. Mg,<R>, R and P. The Mg value is for the magnetic track brake and this is usually much higher than the R-value. If this value is input into the .bin-file the brakes will be too strong when using air brakes only because the fullbrake value will be the value gained from using magnetic track brakes which only apply in an emergency application. In my opinion it is more realistic to use the R-value unless the developer can script the rolling stock so that Emergency brake force is higher than the full service application force.


    Hopefully this was of interest/use to someone. I'd love to hear feedback/opinions because my knowledge can certainly be increased.