Question about Big Boys

[dtrainBNSF1]

Okay just did another test run with BB. Took 2899t. up to Sherman summit in 60 minutes 11 seconds at an average speed of 31 mph. REALLY TOUGH but I think the performance is more believeable. Still plenty of things to tweek yet, but it's getting there. The Challenger is still more of a "challenge" to take over the hill, but that's a bridge I'll cross when I get to it.

[mrennie]

That did it. Where the Big Boy is made of 2 parts I had to change the psi on each part. One thing I'm noticing on my more recent trials is that the boiler is depleting itself of water faster than I can fill it. I lower throttle and reverser settings and end up stalling on the hill. The dev docs make it look like I could possibly increase the size of the cones inside the injectors and feed rate multiplier but wouldn't that also increase how much steam is used in the process?

The only value that affects the steam usage is "Steam usage multiplier". I use 6 for the exhaust injector (feedwater pump actually) and 6.9 for the live injector. To change the rate of filling the boiler, the one to play around with is "Feed rate multiplier". If you know the real life rate of flow (with the FEF-3, I was lucky enough to get those figures from foureightfour), you can run a series of trials and tune the multiplier to get the exact rate.

Nevertheless, in the FEF-3, I've found that on the long climb up towards Dale on the Sherman Hill route, with the feedwater pump on full pressure, it still can't keep up with the rate of consumption of water in the boiler, so I sometimes use the live injector at the same time, in short bursts, or allow the water level to drop below 50% (it catches up again once we're over the hill, of course). You might need to do that too in the Big Boy.

[dtrainBNSF1]

Well I never had the gumption to do that (let the boiler water drop below 50%). I always thought if it did drop below 50% that the sim would end the scenario due to boiler explosion. Well, I'll give it a shot.

[mrennie]

Well I never had the gumption to do that (let the boiler water drop below 50%). I always thought if it did drop below 50% that the sim would end the scenario due to boiler explosion. Well, I'll give it a shot.

Nah, it doesn't blow up until it reaches 0.0000%

[dtrainBNSF1]

Well, here's the result of the latest test. I discovered that the tender did not have the right water and coal levels so I changed the values to 25000gal. and 28t. respectively. I also increased the feed rate multiplier to 2.0. I took the train from Cheyenne to the west end of Hermosa with 107 Sherman Hill boxcars at an average speed of 29mph. It was nerve racking because the boiler water level dropped to 24% around Buford and my speed often dropped to the 21mph range between Speer and Granite. After crossing Sherman summit it became easier as power could be reduced for the downhill run to Dale Junction and water in the boiler could finally catch up. I was working with full throttle and reverser in full forward all the way up because I'm convinced as slow as I was that if I did anything less I would have stalled out. I was left with maybe 11000gal. of water in the tender. Took me just shy of 78 minutes. But MAN talk about total big steam freight satisfaction
I can see why the tonnage ratings I posted on this thread a while back mentioned that fast freights could have a 10% weight reduction - even with a Big Boy 3250t. is MASSIVE and takes plenty of time to fight to Hermosa on main line 1. Now on track 3... Well let's just say 20x.8x3250=52000lbf - 52000lbfxZft-per-second/550=7500hp - 52000lbfxZft-per-second=4125000 - Z=79.32692307692308ft-per-second=just over 54mph.
Sounds like I have a new test to perform on track 3

[mrennie]

Well, here's the result of the latest test. I discovered that the tender did not have the right water and coal levels so I changed the values to 25000gal. and 28t. respectively. I also increased the feed rate multiplier to 2.0. I took the train from Cheyenne to the west end of Hermosa with 107 Sherman Hill boxcars at an average speed of 29mph. It was nerve racking because the boiler water level dropped to 24% around Buford and my speed often dropped to the 21mph range between Speer and Granite. After crossing Sherman summit it became easier as power could be reduced for the downhill run to Dale Junction and water in the boiler could finally catch up. I was working with full throttle and reverser in full forward all the way up because I'm convinced as slow as I was that if I did anything less I would have stalled out. I was left with maybe 11000gal. of water in the tender. Took me just shy of 78 minutes. But MAN talk about total big steam freight satisfaction
I can see why the tonnage ratings I posted on this thread a while back mentioned that fast freights could have a 10% weight reduction - even with a Big Boy 3250t. is MASSIVE and takes plenty of time to fight to Hermosa on main line 1. Now on track 3... Well let's just say 20x.8x3250=52000lbf - 52000lbfxZft-per-second/550=7500hp - 52000lbfxZft-per-second=4125000 - Z=79.32692307692308ft-per-second=just over 54mph.
Sounds like I have a new test to perform on track 3

About the water and coal, remember that the values in the blueprints (and that appear in the F5 HUD) are in Imperial units (remember when Britain had an empire?), not US units. 25,000 US gallons = 20,817 Imperial gals. 28 (US) short tons = 28 * 0.892857143 imperial tons = 25 Imperial tons.

When going up the hill, you definitely shouldn't have the reverser fully forward. It would be acting as a brake (assuming the simulation blueprint and the t.e. versus cutoff curve are set up correctly) and would cause your boiler pressure to drop. You need to hook up the reverser enough to allow the boiler's steam generation to keep up with the consumption from the cylinders. As the boiler pressure increases, so does the pressure in the cylinders (what the F5 HUD mistakenly calls "steam chest pressure") and that helps you to go faster (or maintain speed) too.

Tuning the steam consumption is something that has to be done with great care too. You need to adjust the cylinder "effectivity" (that word does exist in the dictionary, even though I'd have used "effectiveness") so that you get what feels like the right amount of consumption at a given boiler pressure, cut-off and speed (very tricky to do and requires a lot of trials). In the FEF-3, I ended up with a cylinder effectivity of 2. Changing it by even a small amount makes a big difference to the performance.

P.S. In the dev docs, the description for cylinder effectivity is;

<undefined>

Yep, undefined. But it turns out to be one of those secret ingredients that has a huge impact.

[dtrainBNSF1]

When going up the hill, you definitely shouldn't have the reverser fully forward. It would be acting as a brake (assuming the simulation blueprint and the t.e. versus cutoff curve are set up correctly) and would cause your boiler pressure to drop. You need to hook up the reverser enough to allow the boiler's steam generation to keep up with the consumption from the cylinders. As the boiler pressure increases, so does the pressure in the cylinders (what the F5 HUD mistakenly calls "steam chest pressure") and that helps you to go faster (or maintain speed) too.

That's what I've done for high speed running and before I even starting modding I would notice that the loco would "buck" and the speed would increase/decrease sporadically when it was time to shift down, but this last time the loco was still raising steam all the way up the hill at full reverser (which surprised me) and the loco didn't buck. I tried lowering the reverser a few times during the run and speed would drop but after increasing the reverser again speed would pick back up.

From your observations I can surmise that perhaps my boiler settings are too effective to be realistic. I haven't done too much to the boiler, just increased the exhaust limit so that it tops out only when the loco is in full throttle and full reverser and no sooner, changed the superheater to 1.4, changed the max output to 168187.5 and increased the max steam pressure to 300psi. I'll tinker with the effectiveness line and the volume line.

I've also tried tinkering with the .dcsv files to make 80mph achievable (before it was set for 69 mph - speed tests on the TestTrak route prove that the loco now tops out at 80mph).

[mrennie]

When going up the hill, you definitely shouldn't have the reverser fully forward. It would be acting as a brake (assuming the simulation blueprint and the t.e. versus cutoff curve are set up correctly) and would cause your boiler pressure to drop. You need to hook up the reverser enough to allow the boiler's steam generation to keep up with the consumption from the cylinders. As the boiler pressure increases, so does the pressure in the cylinders (what the F5 HUD mistakenly calls "steam chest pressure") and that helps you to go faster (or maintain speed) too.

That's what I've done for high speed running and before I even starting modding I would notice that the loco would "buck" and the speed would increase/decrease sporadically when it was time to shift down, but this last time the loco was still raising steam all the way up the hill at full reverser (which surprised me) and the loco didn't buck. I tried lowering the reverser a few times during the run and speed would drop but after increasing the reverser again speed would pick back up.

From your observations I can surmise that perhaps my boiler settings are too effective to be realistic. I haven't done too much to the boiler, just increased the exhaust limit so that it tops out only when the loco is in full throttle and full reverser and no sooner, changed the superheater to 1.4, changed the max output to 168187.5 and increased the max steam pressure to 300psi. I'll tinker with the effectiveness line and the volume line.

I've also tried tinkering with the .dcsv files to make 80mph achievable (before it was set for 69 mph - speed tests on the TestTrak route prove that the loco now tops out at 80mph).

Yes, I think you need to experiment with the cylinder effectivity so that when you pick up speed, it consumes more steam at full cut-off than the boiler can generate. The rest of the changes you've made sound fine to me. I'm curious to know what exhaust limit you arrived at. For the FEF-3, it's 435,938 (boiler max output is 115,000).

[dtrainBNSF1]

The exhaust limit I've settled on is 130000 which in comparison with your is quite small. I'm curious how fast the FEF-3's steam chest pressure catches up to the boiler pressure with full throttle and full reverser.

[dtrainBNSF1]

When going up the hill, you definitely shouldn't have the reverser fully forward. It would be acting as a brake (assuming the simulation blueprint and the t.e. versus cutoff curve are set up correctly) and would cause your boiler pressure to drop. You need to hook up the reverser enough to allow the boiler's steam generation to keep up with the consumption from the cylinders. As the boiler pressure increases, so does the pressure in the cylinders (what the F5 HUD mistakenly calls "steam chest pressure") and that helps you to go faster (or maintain speed) too.

About the t.e. versus cutoff curve...
I tampered with that, too. I've returned the effectiveness and boiler volume lines back to their default values and the exact same thing is happening as in the previous test: I'm not having to reduce the reverser to conserve steam and at full power and full forward I'm making 79 mph and still producing steam even with the injector on. The t.e. versus cutoff .dscv file values I have after review I think are way too high. I have:
cutoff/tractive effort
0 .18
.1 .45
.2 .55
.3 .74
.4 .75
.5 .82
.6 .87
.7 .94
.75 1.0

I think what I'll do is make a backup of my mods so far and then redownload the Big Boy from Steam so that I can have a clean slate on the t.e. versus cutoff curve and see how the Big Boy responds with the default curve and the mods so far.

[mrennie]

The exhaust limit I've settled on is 130000 which in comparison with your is quite small. I'm curious how fast the FEF-3's steam chest pressure catches up to the boiler pressure with full throttle and full reverser.

The loco has to be moving, of course, but if it's going at 10mph, boiler pressure at 300psi, full throttle, and I then hold down the W key to move the reverser swiftly to the maximum (which in the FEF-3 is an 80.2% cut-off - that reads as 80% on the F3/F4 and 100% on the F5), the "steam chest pressure" on the F5 hits 300psi at the same time as the Johnson bar reaches the "corner".

[mrennie]

Your t.e. versus cut-off curve is almost ok - there's just a strange bump at 30% cut-off (it would be better with 0.65 instead of 0.74), and the value at 0% should be 0.
I've plotted your numbers and then a modified version with those two changes:

ScreenShot004.jpg

I think you can see the improvement.

As for being able to have full throttle, full reverser and still be able to maintain speed and boiler pressure, there's clearly something else wrong in the blueprint. When it's doing that, what do you have for steam generation and steam usage (on the F5)? I suspect the problem is in the cylinder (not boiler) effectivity. You might need to increase the value so that at longer cut-off, the cylinders use more steam.

[dtrainBNSF1]

The exhaust limit I've settled on is 130000 which in comparison with your is quite small. I'm curious how fast the FEF-3's steam chest pressure catches up to the boiler pressure with full throttle and full reverser.

The loco has to be moving, of course, but if it's going at 10mph, boiler pressure at 300psi, full throttle, and I then hold down the W key to move the reverser swiftly to the maximum (which in the FEF-3 is an 80.2% cut-off - that reads as 80% on the F3/F4 and 100% on the F5), the "steam chest pressure" on the F5 hits 300psi at the same time as the Johnson bar reaches the "corner".

I've always tested it standing still. Doing the test with your method shows that I'm actually still too low

I've gone ahead and changed the dscv file. I haven't done a "full scale" test yet. I just redownloaded the Big Boy after making a backup of the mods and I've been editing the simulation file one variable at a time and performing speed trials on on the TestTrak route. So far the only variable in the boiler section that's rendered lowering the reverser as unnecessary is so far the superheater. Looking at the cylinder effectivity value shows that it's at 2. I'll be running tests the rest of the morning playing with more variables, including the cylinder effectivity.

I have to say getting critique from you is an honor. I'm learning a lot

[dtrainBNSF1]

Took a break for a bit. I started playing with the cylinder effectivity value. I just put it down to 1 and restored the superheater value to 1.4 and the Big Boy is suddenly acting like an entirely different loco Steam pressure isn't building nearly as fast as before, acceleration is slower and much more controllable, and even though the loco doesn't "buck" acceleration and steam production does halt after a time until after the reverser has been lower . 1 is still too low, but I've been going up by .1 for every test. I wouldn't be surprised if I hit the sweet spot by maybe 1.3 or so. And even after that I'll probably go up by .01 to fine tune it further.

[mrennie]

Took a break for a bit. I started playing with the cylinder effectivity value. I just put it down to 1 and restored the superheater value to 1.4 and the Big Boy is suddenly acting like an entirely different loco Steam pressure isn't building nearly as fast as before, acceleration is slower and much more controllable, and even though the loco doesn't "buck" acceleration and steam production does halt after a time until after the reverser has been lower . 1 is still too low, but I've been going up by .1 for every test. I wouldn't be surprised if I hit the sweet spot by maybe 1.3 or so. And even after that I'll probably go up by .01 to fine tune it further.

When you say "Steam pressure isn't building nearly as fast ", I take it you mean the "steam chest pressure" shown in the F5 HUD. That's what I'd expect - lowering the cylinder effectivity makes the "steam chest pressure" (average pressure in the cylinder) rise more slowly (which in turn makes the loco less "jumpy").

Something you do need to do is make sure that cylinder effectivity is set to a value that makes the steam usage just exceed the maximum boiler output when the loco is at it's maximum speed, with the cut-off shortened to 10% or less. The main things that limit a steam loco's speed are friction, drag and the boiler horsepower (basically, the max steam generation). If you reach the top speed and the boiler is still generating more steam than the cylinders are using, the loco will probably be able to keep on accelerating (because it's still got spare boiler horsepower to maintain boiler steam pressure, so you can lengthen the cut-off more, to get more tractive effort and accelerate). To stop that, you have to do speed trials and adjust that cylinder effectivity until, at the top speed and approx. 10% cut-off (or lower speed but longer cut-off), the cylinders are using all the steam the boiler can generate

Shortening the cut-off (reducing the reverser) doesn't increase steam generation directly, but there is an indirect effect. What happens is that the steam usage reduces (steam enters the cylinders for less time on each piston stroke, but there's more time for the steam to expand in the cylinder) and that allows the boiler to build up more pressure, plus the back pressure is reduced (back pressure is what acts as a brake when you reach a certain speed, just like in a car when you reach a certain speed, or rather a certain revs, and need to go up a gear in order to go faster), thus you go faster, and by going faster, more air goes into the firebox through the open damper door, which aids the combustion, which in turn makes the boiler generate more steam.

Maybe you can see why it's taken me many months of trials (some on Sherman Hill, some on the fast sections of the NEC) to tune the FEF-3's performance