Dodgy physics

[TrainMaster1]

Not all what happens is let's say you have grabbed 10 lbs instead of 6 or 7 as desired. In a standard system you would now have 80 lbs left in the reservoir (90 standard-10 you took). You now say oops too much and release that. There is no way I know to go from 10 back down to 7 successfully. The minute you release you go down to no application and have to reset to 7 (now without a recharge time at all you have 73 lbs left. 80-7=73.) Remember we are referring to the reduction in the brake pipe not the force applied to the wheels here.

This is known as fanning the brakes...and this is where guys get themselves in trouble. Case in point on the SP Cascades session....train coming downhill for a meet was going into the siding at Summit. Unfortunately for him, he had made several applications on the way down always drawing too much and quickly making releases. As he sat in the siding, he starts to slide past the switch and so we had to cheat a little and let him drop into reverse and hold a notch or two (plus run out and set some handbrakes quick) to keep his nose in the siding as the train on the main passed him. Same thing would happen in the real world. You run out of air and you could be looking at the same situation.

That is why I teach in both sim and when I was doing it on the road how to set and hold that minimum application until you know you are at the bottom of the hill. Some brakes recharge quicker than others but you don't want to find out the hard way what type your train has.

So you do not have to wait for a complete recharge but I would never release until I am off the grade completely and can control the action in the train without unnecessary chance of damage to equipment or me.

Nick

[TrainMaster1]

Sorry Kali missed the DB questions at the end there....you would not be using DB usually uphill for any reason on any loco. Gravity most often gives you all the help you need.

If you use a heavier application at the front you risk the momentum of the train coming and possibly derailing or at least damaging cargo. Think about riding a bike and jamming the front brakes on...guess who most likely will have momentum carry them them over the handlebars. That force is sitting in the train behind you. Air alone should handle you uphill.

DB operates best above the 8-10 mph range. Below this speed the motor cannot really generate much in the way of resistance to slow you down and this is where now Independent Brakes become useful.

In DC motors you have a speed known as Lowest Continuous Speed which is somewhere around 9-11 mph based upon loco model. If your speed stays in this range you will turn the traction motors into paperweights. The Hours of Service meter in the cab would be in the red zone in this situation warning you that you need to either increase speed (if possible) or stop the movement as you are underpowered for the task at hand and will destroy the motors.

This is why AC traction motors on long slow heavy trains are so popular they do not have this problem. You can pull that coal or grain train up the hill without worrying about a melt down.

Nick

[MikeK]

Can't wait until someone figures out how to get a sim to run in "picket fence" mode. That will show you how to control a train on Cajon. This is where you can have the DPUs operate a different throttle setting and/or brake setting to bunch slack or hold a train back as you negotiate a downgrade. All controlled from the friendly confines of the lead loco with the DPUs dialed in.

I would love to see this too. From a user interface point of view, there could be a second "F4" view, perhaps "Shift-F4" with a different colour background so you know that you are looking at the DPU controls instead of the head end controls.

[MikeK]

Kali, I tried your SD40-2 update last night.

Thank you so much for the effort, it is great to see someone at least trying to fix some of the issues with the sim.

One thing I noticed though if I watched the data using the F5 view, is that when the brakes are released the "brake pipe" pressure still recharges extremely fast, whereas the "brake cylinder" pressure drops very slowly.

Someone please correct me if I am wrong, but I would have thought that it would be the other way around. From a steady braking state, any increase in brake pipe pressure would cause the brakes to immediately release. Obviously on a long train it would take some time for that change in pressure to propagate down the length of the train, but when any individual car sees the change in pressure, the brakes release.

So for example, say the brakes are on, and the situation looks like this:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 80 - 25 - Applied
50 cars in - 80 - 25 - Applied
100 cars in - 80 - 25 - Applied


If you then release the brakes, after a few seconds it might look like this:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 81 - 0 - Release
50 cars in - 80 - 25 - Applied
100 cars in - 80 - 25 - Applied



After a few seconds more, the change in pressure has now reached the middle of the train:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 81 - 0 - Released
50 cars in - 81 - 0 - Released
100 cars in - 80 - 25 - Applied



Finally the change in pressure makes it to the rear of the train. At the same time the pumps on the locos are still increasing the pressure at the head end:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 82 - 0 - Released
50 cars in - 81 - 0 - Released
100 cars in - 81 - 0 - Released



A few minutes later:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 87 - 0 - Released
50 cars in - 86 - 0 - Released
100 cars in - 85 - 0 - Released



Finally after several minutes:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 90 - 0 - Released
50 cars in - 90 - 0 - Released
100 cars in - 90 - 0 - Released

Now full braking capability has been restored. Now if the same 10lbs brake pipe reduction is made:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 80 - 25 - Applied
50 cars in - 90 - 0 - Released
100 cars in - 90 - 0 - Released



After the drop in pressure has made it halfway down the train:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 80 - 25 - Applied
50 cars in - 80 - 25 - Applied
100 cars in - 90 - 0 - Released



When the drop in pressure finally makes it to the back of the train:

Location - Pipe pressure - Brake cylinder pressure - Brake state
Head end - 80 - 25 - Applied
50 cars in - 80 - 25 - Applied
100 cars in - 80 - 25 - Applied


I believe this is how the braking system should work. I do not have any helpful concrete numbers regarding how quickly changes in brake pipe pressure move from car to car, or how long it takes to increase the pressure in the brake pipe on a long train. I do remember seeing an issue of Trains magazine sometime in the last year or two that focused on distributed power, and they had some diagrams indicating that it could take 20 - 30 seconds for a change in pressure to make it from one end of a long train to the other. To me this means that when the brakes are applied, after 20-30 seconds the brake would be on at every car. When they are released, 20 to 30 seconds later they would be fully released at every car. To do it properly, the number of locos would have to be a factor. For example, with 4 locos instead of 2, that is twice as many compressors, so it should take half the time.

In other words, the 2 big problems are that firstly the game doesn't simulate the pressure in the brake pipe at each car, it treats the whole train as having the same pressure, and secondly the pressure in the brake pipe increases waaaaay to fast, meaning that you can repeated apply and release the brakes with no fear of running out, which isn't realistic.

Another improvement that I would love to see if it could happen is to see changes in the brake pipe pressure go not just from front to rear, but from wherever a locomotive is in the train, including mid train and rear DPUs. That one I am guessing will need changes from railsim.com :)

I hope this is helpful (and accurate!).

Mike.

[Kali]

I would imagine brake application propagation is quite fast; one reason why it's so slow to release a single pipe system is you've got to recharge all the reservoirs on the cars from the same pipe ( which is why we mostly use twin pipe systems with a Main Reservoir Pipe over here ). I believe the purpose of a retainer on a US car is to mitigate that a bit? US brakes are somewhat unnecessarily complicated.

Brake cylinder pressure at it's most basic is an effect of the pipe pressure - that's how airbrakes work in the first place! so unless there's a system on each car to rapidly release the brakes when the pipe pressure starts rising - which there might well be but I'm pretty sure isn't modelled - then cyl pressure is going to rise slower than pipe pressure. Irrespective of this, you can't make RW cylinder pressure rise faster than pipe pressure anyway.

Nick: ok, so there is always a full release, can't do anything about that. So now we have 10lbs->oops! release-> wait 30s or however long for full release -> make new application -> 7lbs. What happens if you don't wait to reapply, nothing bar you moving the lever I guess? if the brake handle is somewhere in the service range when the full release is complete I take it there's an immediate application again, or do you have to reset the lever first?. I am pretty sure I can't do anything about running out of air, but given the length of time for release of a long train now having no control of the brakes for a couple of minutes makes you stop & think anyway.

The issue with the dynamics was from me thinking if the head of the train is on a downgrade and the middle/end ( wherever the DPU are ) is still on an upgrade.

[Rich_S]

ok, so there is always a full release, can't do anything about that. So now we have 10lbs->oops! release-> wait 30s or however long for full release -> make new application -> 7lbs. What happens if you don't wait to reapply, nothing bar you moving the lever I guess? if the brake handle is somewhere in the service range when the full release is complete I take it there's an immediate application again, or do you have to reset the lever first?. I am pretty sure I can't do anything about running out of air, but given the length of time for release of a long train now having no control of the brakes for a couple of minutes makes you stop & think anyway.

Hi Kali, I was told, you never, never, never, never release your brakes once you've made an application and you're heading down grade. If you wanted 7 lbs and took 10 lbs, don't release, drag the train down the hill. I guess you could think of the automatic brake handle like a cork in a jug held upside down. Pull the cork out and the liquid will run out of the bottle until you put the cork back in. Once you turn the bottle right side up, you have to refill it completely before you can use it again. If you move the brake handle to release then move it back to some other position, the release stopped, the minute you moved it away from the release position. This is a giant NO, NO as now you'll have funky things happening. Part of the train is starting to release and the rear still has the last application. Your only option at this point is to drop the brake pipe even further to try and regain control. then things come grinding to a halt and now your conductor is going to be very upset, as he now has to go out and start setting hand brakes on let's say the first 30 cars. The automatic brake valve is designed to be a pressure maintaining device, ie drop 10 lbs and it should hold that pressure until reset (released) The handle must be kept in the release position until the brake pipe is completely recharged. Unfortunately in the real world you also have brake pipe leakage that throws a monkey wrench into the works. You make a minimum reduction of 7 lbs, but you also have a 1 lb leak every 5 minues. After 15 minutes you now have a 10 lbs brake pipe reduction and you're still not to the bottom of the grade. I know this is not modeled in Rail Works, but I mention it just to give you a little more understanding of the what goes on, on this side of the pond :)

Regards,
Rich S.

[Kali]

Aha! now it's clear - I was expecting some sort of valve opened in release that wouldn't close until you got full pipe pressure back. How things work and how you should drive aren't always the same thing :) it's possible to model leaks, we do it for vacuum braked stock that can't hold a vacuum to save it's life - that's actually a nice idea - obviously can't do anything about there being different pressures in different parts of the train.

I'm a bit hesitant to say this but actually we *could* model the entire train properly, but that would involve making every car a 0 powered engine and hijacking the DB on them to act as the autobrake, as you can imagine that is not exactly the sanest thing to do!

[MikeK]

Kali, have you tired OpenRails?

In the latest version if you go through the F5 views there is one that shows what the brakes are doing throughout the train.

I believe they are a lot closer to reality than RW is currently.

[Kali]

I don't have the MSTS requisites for OpenRails; I like where it's going with the performance modelling though. As long as it stays fun to use!

[GaryG]

Hi Rich_S

A leaking trainline is normally not a problem unless excessive which can happen when gaskets harden in extremely cold weather. CPR used to use an air repeater car mid-train to get around the cold weather leakage problem. With DPU's this isn't a problem now; I assume air can be supplied from both ends so the repeaters are not needed.

Current loco brake control stands with self-equalization either let air out or let air in to keep the trainline at the equalization pressure which is set by the brake handle position when between the Lap and Full Application positions. What you described can still occur if the handle is left in the Lap position.

I think this info is reasonable accurate...

GaryG

[Rich_S]

Hi Rich_S

A leaking trainline is normally not a problem unless excessive which can happen when gaskets harden in extremely cold weather. CPR used to use an air repeater car mid-train to get around the cold weather leakage problem. With DPU's this isn't a problem now; I assume air can be supplied from both ends so the repeaters are not needed.

Current loco brake control stands with self-equalization either let air out or let air in to keep the trainline at the equalization pressure which is set by the brake handle position when between the Lap and Full Application positions. What you described can still occur if the handle is left in the Lap position.

I think this info is reasonable accurate...

GaryG

Hi Gary, A leaking brake pipe can be a big problem, so much so that you are still required to perform a brake pipe leakage test as part of your departure tests. The 26L brake stand does not contain a lap position, the valve is self lapping. The equalization only applies to the equalizing reservoir. Your brake handle controls the equalizing reservoir and the brake pipe just follows what the equalizing reservoir does. What does all of this mean, simply; you make a 10 lbs reduction of the equalizing reservoir, and the brake pipe makes a 10 lbs reduction. The ABD valves on all of the cars detect this 10 lbs reduction in the brake pipe and send 25 lbs of air pressure from the cars air tank to the cars brake cylinder. Now the equalizing reservoir tries to maintain that 10 lbs drop (remember you are allowed to have some brake pipe leakage, but you are not allowed to have any equalizing reservoir leakage). If your brake pipe is leaking off, the ABD valves on each car will continue to respond to each drop in brake pipe pressure. As for DPU's, I would think they do not supply air to the brake pipe as their automatic brake handles should be in the cut out position. The brake pipe should be controlled from the head end only. I've not worked with DPU equipment, so it maybe possible they have something setup to charge the brake pipe when the lead units brake handle is in the release position, this I'm not sure of?

Regards,
Rich S.

P.S. The train line is the MU cable that connect all units electrically in a consists, the brake pipe is used to charge the cars reservoir and control the brakes on the train

[Kali]

Or to summarize, the EQ system is to show the driver what he just did, not what he thinks he did :).

I have a massively slower charging air tank now, but I can't seem to find where ( or if you even can ) set how much pressure drop in the tank = how much raised in the pipe. There's one or two likely settings that didn't actually seem to change anything when I twiddled them.

[TrainMaster1]

Brakes are indeed controlled from the head end only as the DPU's throttle is as well. Although that can be set to different throttle notch than the head end to bunch slack in what is know as running a "picket fence".

To see what pressure is in the pipe... do the gauges in the cab for RW engines accurately portray the 90 lbs to start and show how much of a reduction you have taken? If Yes, you need to look at the gauge in the engine not what you have the game controller set to...once you learn how the engine reacts to different settings then you can use the game setting matching the desired brake reduction to achieve the desired results you need.

Remember the formula number 2.5 x as this is the amount of force going against the wheels. A 10 lb reduction place 25 lbs against the wheels of the train.

Hope this helps.

Nick

[arizonachris]

Gauges in cab? He he he. Lucky if the speedometer works. Most cabs have minimal gauges that work at all. No brake pressures that I can recall. Use the F5 HUD (you have to shut off the new F4 HUD first) F5 will show brake pipe and brake cylinder pressures, and the percent (Not notch!) of brakes applied, and status IE: release, running, self lap limited, etc. I think that's about it.

Nick, do you have Railworks yet, and have you run any routes or scenarios? You're gonna find it........... interesting, I think.

[Kali]

The SD40 gauges work fine ( as do all european stock ). I just can't remember which they are - train pipe + cyl pressure on one gauge, I think reservoir on the other but I can't remember what the last needle is. A working EQ gauge would need a flowmeter to be any use - or I guess you just go when the reservoir pressure stops falling ( or in RW's case when the cyl pressure gets close to 0 ). I think you can get EQ pressure in a control and thus on a dial, but I'm not certain yet.