Another Piece of the puzzle....

[Rich_S]

Hello Group,
In trying to get Rail Works locomotives to perform like their prototypes I've been peaking under the the RSC hood so to speak and have found some areas to tweak. One of the very first things I discovered with Rail Works is just how far out of the ball park the Automatic Brake Handle settings are A minimum reduction does not occur at approx. 30% of the handle movement, it's more like 8%. I worked with Mike Simpson on this and he added my mods' to RW_Tools. Well add another setting to the list of tweaks It's found in the locomotives simulation file and the string tag is CylinderPressureForBrakeToCutPower. Since I started using Rail Works, one of the things that really bothered me is is the inability to load the engine against the brakes. With my Automatic air brake settings you can load against the brakes but only to a certain point. After looking through the locomotives simulation file I noticed the tag CylinderPressureForBrakeToCutPower with a value of 30. Changing this value to 99 will allow you to load against the brakes even with a full brake pipe reduction. Now we can finally drag them down the hill like they do on the prototype, when we make too much of a brake pipe reduction, unless you want to ruin the day of your conductor and brakeman by stopping on the hill and having them tie on hand brakes so you can recharge the train line

Regards,
Rich S.

[Kali]

Set it to 0 ( the CylinderPressureForBrakeToCutPower thing ), it disables the power cutting totally. While I was searching for something else I noticed you asked me that before - sorry, forgot to mention it when I worked that out!

Min app is a bit funny - I guess it's a bit easier for US brakes where any release is total, fully self-lapping brakes like euro ones you can apply to min app & then release a bit, and you've got below min app. Annoying.

[gwgardner]

what does 'load against the brakes' mean, please

[Kali]

Applying power with the brakes on. Or well, a bit more detail:

"Loading" is ( apparently a US phrase ) the term used to describe how the power system builds power ( or in Rich's example, just another term for applying power ) - so on an old GE or something just moving the throttle won't give you any more effort for quite a while, the engine has to rev up and then the electrics have to sort themselves out to send more juice to the motors afterwards; you'll find people talking about "slow loading", that's all it is. A SD40 or similar age EMD is a lot quicker ( new ones are slow ) and a switcher would be faster still, but none of them are as instant as a default RW engine.

If you imagine you're facing up a hill sitting in an old GE, if you just let the brakes off & apply power then you'll be rolling backwards for a while until it's actually got some power to the wheels. So, you open the throttle, let it build some revs, then let it build some current, and let the brakes off after that. RW won't let you do the "building current" bit usually.

[Rich_S]

Set it to 0 ( the CylinderPressureForBrakeToCutPower thing ), it disables the power cutting totally. While I was searching for something else I noticed you asked me that before - sorry, forgot to mention it when I worked that out!

Min app is a bit funny - I guess it's a bit easier for US brakes where any release is total, fully self-lapping brakes like euro ones you can apply to min app & then release a bit, and you've got below min app. Annoying.

Hi Kali,
Thank you for the reply, I wasn't sure what zero would do, so I just went for a very high value. The 26L and newer brake systems used here in North America are self-lapping. On older brakes like the 6L crews would report problems like you mentioned when making a minimum reduction, that is why it was a common practice after making a minimum reduction (or on some railroads "SET") and once you stopped or reached the desired speed, you make another small reduction, then release. It seems some AB values would not see the release after a minimum reduction so the brakes on that car would stay applied. Yes I agree, on US stock, you reduce the equalizing pressure, which reduces the brake pipe pressure and the brake values on the cars send 2.5 x the brake pipe reduction to the cars brake cylinders and since it's a single pipe system, the only way you get a release is raise the brake pipe back to the feed value pressure setting.

Regards,
Rich S.

[MikeK]

In railworks you can apply and release the brakes over and over without any issue.

In reality however, when you apply the brakes, the amount of force you get from the brakes depends on how much the pressure in the brake pipe has dropped. For example, if the brake pipe pressure is 90psi and you apply the brakes, dropping the pressure to 84 psi then you get 6psi worth of braking force.

When you release the brakes, in railworks that brake pipe pressure goes instantly back to 90psi, but in reality it can take minutes to recharge that brake pipe pressure. If the brakes are needed again when the brake pipe pressure is only up to 85psi, then the pressure must be reduced to 79 psi to get that same 6psi reduction. Do this a few times in a row without letting the brake pipe pressure recharge and you can see that a train will quickly have no brakes at all.

Because of this, when the brakes are applied, they normally are never released until the train reaches the bottom of the grade. If there is a section in the middle of the grade where it flattens out a bit, instead of releasing the brakes and risking not having enough air when the brakes are needed again, the engineer will add throttle and drag the train over the flatter section.

Here is an excellent description of how the brakes on US equipment work: http://www.alkrug.vcn.com/rrfacts/brakes.htm

[MikeK]

Rich: thanks for the settings that are built into RW_Tools! :)

[Rich_S]

what does 'load against the brakes' mean, please

Hi gwgardner,
Just to build on Kali answer, if you take a locomotive like the SD40-2, you have both a Main Generator and a Auxiliary Generator. When the engineer moves the throttle, that actually triggers the engine's governor to increase the speed of the diesel engine. The Auxiliary Generator, which is also mechanically coupled to the Diesel engine, supplies voltage to the Main Generators field. Since the Main Generator is directly linked to the Diesel engine, the increase in the diesel engine RPM's also increases the RPM's of the Stator in the Man Generator, causing it to pass through lines of flux. Since the Diesel engine is also increasing the speed of the Aux Gen, it also increases it's output, sending more current to the Main Generators field, which increases the size of the field. The current produced in the Main Generator is then sent to the traction motors to move the locomotive and hopefully the train As you can see, for all of this to take place requires a few seconds. Also like Kali mentioned, newer locomotives like the EMD SD60 and SD70 series locomotives and the GE Dash 9's and EVO series locomotives all have electronics controlling the diesel engines. Because of this computer control, they are just a tad slower in loading times, but they more than make up for it in control. Hopefully this makes some sense, and yes on the railroad we call the above process loading, when a locomotive stops loading (ammeter stays at zero when the throttle is increased toward run 8) this condition is known as "Not Loading or Not Loading Properly" Hopefully this gives you a little better understanding of what goes on under the hood

Regards,
Rich S.

[Rich_S]

Rich: thanks for the settings that are built into RW_Tools! :)

Hi Mike, You are welcome. The very first train I ran in Rail Works I went in into panic when I did what I thought should have been a minimum reduction and nothing happened. I was quickly scanning through the user manual trying to make sure I did not have to cut-in the Automatic brake Once I realized that the settings RSC was using was not even close to what they should be for North American diesel locomotives with 26L, EPIC, NORAIR and CCBII, I did some adjusting. Mike was kind enough to add the code to his RW_Tools, which is a real blessing when RSC decides to update engine files. I figure a little bit at a time all of us can make this a pretty nice train sim


Regards,
Rich S.

[Kali]

European brakes are ( since the 50s anyway and since always with UK vacuum brakes ) self lapping in both directions, so you can just adjust the brake to whatever you need without having to dump the entire cylinder pressure & start over ( which saves a lot of filling reservoirs too ) - but I'm reasonably sure you can't reduce below minimum application, which you can in RW. Well, actually it's mostly down to the control; the usual combined desk one you get in older diesels/electrics has a usable range from min app to full service, so it won't let you go below min app unless you want a full release. Old vacuum brake controllers are more or less just valves to let air into the pipe, so you can just use whatever the ejector system is on the locomotive to let the brakes off to what you want. You can set a RW brake controller up to not go below min app, but then the usable brake range starts about 1/3d of the way round it's motion...

It takes about 20s to fully charge one of our modern heavier trains, yey for dual pipe brakes and short trains :) the odd train of single pipe stock takes a bit longer, but still under a minute iirc.

And to expand on Rich's answer a bit more - the original reason GEs took forever to load and Alcos ( which are much the same inside, 4-stroke turbocharged of similar construction ) didn't, is the reason people seem to love Alcos - the smoke. The amount of fuel the engine is using is controlled by the governer, which tries to keep it going at whatever RPM you set it to with the controller; move up a notch and it sends more fuel because the engine RPM is now too low. Easy enough, just like your right foot and your eyes reading your speedo :). However, an amount of fuel needs a similar amount of air to burn properly - if it doesn't it gets burned in the exhaust, and that causes smoke. ( and fire! )

So why do Alcos smoke and not GEs? because Alcos were generally set up to get the engine RPM higher as fast as possible, so you could add more load onto the generator & get the train moving or just to be more responsive. What happens is the engine spins up before the turbocharger spins up ( the turbo uses the exhaust pressure to shove more air into the intake of the engine, but it takes time to get it spinning ), so there's too much fuel for the amount of air coming in. GEs were set up so the engine could build RPM up more slowly, give the turbo a chance to spin up, and also to not put too much load on the generator too soon so the system didn't have to feed too much fuel to the engine too quickly. Of course then you have to wait ages for the thing to build power, hence one reason for "loading against the brakes". You could always tweak a GE afterwards to speed it up, if you weren't too bothered about the environment...

I have read ( obviously I've never driven one! ) about dash7 or dash8 series taking 2 mins or so at least to get usable tractive effort. Two-stroke EMD engines were more responsive anyway, and secondly EMD turbos are physically driven by the engine at lower notches ( technically making them superchargers at that point, I guess ) so there's much less waiting around.

The point of all this rambling is that the modern locomotives load slowly for the same reason old GEs do, it's cleaner & more efficient. And as Rich said, the electronics & control systems are massively better. There's another trick RSC hasn't even gone near ( other than something I hacked up myself, I'm not sure anyone has actually ), is that recent US diesels get to high RPM way before notch 8. That wonderful guy Al Krug has a really useful page about Dash-9s which I'm going to attempt to convert into a decent RW implementation when I get time - experiments with SD40s are looking promising - but basically it's at the same RPM from notch 3 to 7, and only jumps a little from there to notch 8. It's the same with our Class 70s here ( also GE ), max RPM in notch 4.

[thecanadianrail]

In railworks you can apply and release the brakes over and over without any issue.

In reality however, when you apply the brakes, the amount of force you get from the brakes depends on how much the pressure in the brake pipe has dropped. For example, if the brake pipe pressure is 90psi and you apply the brakes, dropping the pressure to 84 psi then you get 6psi worth of braking force.

When you release the brakes, in railworks that brake pipe pressure goes instantly back to 90psi, but in reality it can take minutes to recharge that brake pipe pressure. If the brakes are needed again when the brake pipe pressure is only up to 85psi, then the pressure must be reduced to 79 psi to get that same 6psi reduction. Do this a few times in a row without letting the brake pipe pressure recharge and you can see that a train will quickly have no brakes at all.

Because of this, when the brakes are applied, they normally are never released until the train reaches the bottom of the grade. If there is a section in the middle of the grade where it flattens out a bit, instead of releasing the brakes and risking not having enough air when the brakes are needed again, the engineer will add throttle and drag the train over the flatter section.

Here is an excellent description of how the brakes on US equipment work: http://www.alkrug.vcn.com/rrfacts/brakes.htm

actualy RW does do this, i have had problems where i need to apply 60-70% brake for a good ammount of pressure going to the brakes, the problem in RW is that the lines recharge to quickly for most people to notice this but if lets say that you are hard on only using air brakes on cajon pass going down hill, you will see that once in a while you will get this effect.

[SMMDigital]

Hmmm, interesting. Have already changed the C398 simulation values to reflect what is being talked about here.

[gwgardner]

Thanks for the explanations. So we should go into RWTools now and adjust this for some/all our engines?

[Rich_S]

In railworks you can apply and release the brakes over and over without any issue.

In reality however, when you apply the brakes, the amount of force you get from the brakes depends on how much the pressure in the brake pipe has dropped. For example, if the brake pipe pressure is 90psi and you apply the brakes, dropping the pressure to 84 psi then you get 6psi worth of braking force.

Hi Mike, If you make a 6 lbs reduction of the brake pipe, you actually get 15 lbs of brake pressure in the cars brake cylinder.

When you release the brakes, in railworks that brake pipe pressure goes instantly back to 90psi, but in reality it can take minutes to recharge that brake pipe pressure. If the brakes are needed again when the brake pipe pressure is only up to 85psi, then the pressure must be reduced to 79 psi to get that same 6psi reduction. Do this a few times in a row without letting the brake pipe pressure recharge and you can see that a train will quickly have no brakes at all.

Because of this, when the brakes are applied, they normally are never released until the train reaches the bottom of the grade. If there is a section in the middle of the grade where it flattens out a bit, instead of releasing the brakes and risking not having enough air when the brakes are needed again, the engineer will add throttle and drag the train over the flatter section.

Some people call what you describe above as "Peeing away the air", which are quick applications and releases without allowing the brake pipe to fully recharge. When you do this you'll eventually get what is known as equalization, meaning the air pressure in the service reservoir on the cars equals the air pressure in the brake pipe, aka you are now along for the ride. Once you have reached equalization, you only have one more option left, emergency. The air tanks on freight and passenger cars actually have two compartments, one is the service side and the other is the emergency side. If you put the handle in emergency (named "The Big Hole" because of the rapid venting of the brake pipe) the ABD valve senses the rapid discharge and uses the air in the emergency side of the reservoir to apply the brakes, leaving you again along for the ride

When it comes down to it, we kind of walk a thin line for recharging times, because lets face it, who wants to wait 2 to 5 minutes for the brake pipe to recharge all of the air tanks on a 50 to 100 car freight train, but at the same token as Mike points out, you'll never "Pee away your air" because Rail Works does recharge the system a tad to fast. I guess the bottom line is, how much of a compromise are we willing to make between total realism and train sim fun?


Regards,
Rich S.

[Rich_S]

So why do Alcos smoke and not GEs? because Alcos were generally set up to get the engine RPM higher as fast as possible, so you could add more load onto the generator & get the train moving or just to be more responsive. What happens is the engine spins up before the turbocharger spins up ( the turbo uses the exhaust pressure to shove more air into the intake of the engine, but it takes time to get it spinning ), so there's too much fuel for the amount of air coming in. GEs were set up so the engine could build RPM up more slowly, give the turbo a chance to spin up, and also to not put too much load on the generator too soon so the system didn't have to feed too much fuel to the engine too quickly. Of course then you have to wait ages for the thing to build power, hence one reason for "loading against the brakes". You could always tweak a GE afterwards to speed it up, if you weren't too bothered about the environment...

On the Dash 8's you can make them smoke just like an ALCO by pushing in on the lay shaft since they still have a mechanical governor. Dash 9's and above have a ECU (Electronic Governing Unit), no layshft or mechanical governor. Yes, ALCO's suffered from what was referred to as Turbo Charger lag.

I have read ( obviously I've never driven one! ) about dash7 or dash8 series taking 2 mins or so at least to get usable tractive effort. Two-stroke EMD engines were more responsive anyway, and secondly EMD turbos are physically driven by the engine at lower notches ( technically making them superchargers at that point, I guess ) so there's much less waiting around.

Dash 8's are not that slow, if it's taking 2 minutes to load there is a problem. Now if you wipe the throttle, yes it may take the governor 2 minutes to allow the diesel engine to reach full RPM's. I don't know if I'd say EMD's are more responsive because of their Turbocharger. Of course that was always a selling point with EMD, "Every stroke is a power stroke", but if that is the case then why do the EMD 710's load at just about the same time as the GE's Cooper Bessemer 4 cycle? You are correct below notch 5, the EMD uses a mechanical blower to force the exhaust out of cylinder and force fresh air into the cylinder. But the EMD Turbocharger also contains a clutch pack and above notch 5 the blower is disengaged and the Turbo runs off the exhaust. On a side note, GE's and ALCO's used the same electrical components, because they were made by GE. It's also amazing how similar the GE diesel engine is in appearance to the ALCO diesel engine.

The point of all this rambling is that the modern locomotives load slowly for the same reason old GEs do, it's cleaner & more efficient. And as Rich said, the electronics & control systems are massively better. There's another trick RSC hasn't even gone near ( other than something I hacked up myself, I'm not sure anyone has actually ), is that recent US diesels get to high RPM way before notch 8. That wonderful guy Al Krug has a really useful page about Dash-9s which I'm going to attempt to convert into a decent RW implementation when I get time - experiments with SD40s are looking promising - but basically it's at the same RPM from notch 3 to 7, and only jumps a little from there to notch 8. It's the same with our Class 70s here ( also GE ), max RPM in notch 4.

Not sure what Al Krug is talking about? but from everything I've seen thus far, each notch on the throttle still has a set RPM for the diesel engine speed. Al maybe confusing diesel engine RPM with main generator control. EMD's have a device on their newer units called a chopper. Basically the computer can control the field of the main generator using gated diodes, so in theory you can be at a lower throttle notch, but if the computer senses a higher demand, it can gate the diodes for a longer period of time creating a higher output from the main generator. GE's have the same thing, but I always liked the name of the EMD device, sounds cool

Regards,
Rich S.