RSC 2-8-0 CONSOLIDATION

[bpetit]

mrennie, how did you caculate your maxforce from its tractive effort?

[mrennie]

mrennie, how did you caculate your maxforce from its tractive effort?

Ah, trick question

There's a well-known, simple formula for maximum starting tractive effort, but that doesn't lead you directly to the drawbar pull or anything else that is in the engine simulation blueprint. Nor do we have a dynamometer car to measure it on a test run. So I did the next best thing. There's another, much more complicated formula, in a really good book by Prof. Llewellyn V. Ludy, M.E., written in 1920 (the same year the Consolidation was built) that quite accurately gives the number of tons of train, including engine and tender, which can be hauled over a certain grade with given starting and ending speeds. The parameters include the cylinder dimensions, mean effective pressure (during the complete cycle of driving and exhaust strokes), driver diameter (including tires), wind resistance (estimated at 8lbs per ton of train), and the grade (feet per mile) and grade length. I calculated it for a 20 car consist going up the 1.1% grade out of Altoona, entering it at 10MPH, to see where, in theory, I should stall out, and then did a trial. I just adjusted the engine parameters until I stalled out at the right spot. I also tweaked parameters until it simply felt right (no Formula 1 Grand Prix starts for example).

By the way, the tractive effort came out at 34,970lbs, assuming 15% losses. Not bad really (and mainly thanks to those teeny weeny drivers).

[mrennie]

By the way, the tractive effort came out at 34,970lbs, assuming 15% losses. Not bad really (and mainly thanks to those teeny weeny drivers).

I've just had an idea. I already read the tractive effort in the LUA script, and use it to control the colour of the stack smoke. I'll use the debugger to print out its maximum value when starting the loco, and check that it agrees with my calculation. If it doesn't, I can tweak the blueprint values until it does.

EDIT: Nope, doesn't work. The function GetTractiveEffort just returns a value in the range 0.0 to 1.0 (actually the most it reached with the sanders on was 0.64). It's not the t.e. in lbs.

[mrennie]

I've managed to work out how to get more than four positions on the train brake handle.

I've now got:

Release
Running
Hold
Hold Lapped
Continuous Service
Emergency

I've got a question though. What would be a realistic rate at which the compressor would recharge the brake pipe? I want to give the player an incentive to use the brakes properly by making it more likely to run out of pressure in the train cars' reservoirs if the engineer makes brake reductions too often. At the moment, the recharge rate is set at 10psi per second, so it doesn't really take long at all to get back to normal pressure after applying the brakes (making a service reduction). What would be more realistic? I thought perhaps 1psi/s might be better.

[thecanadianrail]

5psi per second sounds a little more realistic for these types of brakes and since this loco would realistically only be doing shorter trains this may be accurate, remember the longer the train the longer the charge rate.

[mrennie]

5psi per second sounds a little more realistic for these types of brakes and since this loco would realistically only be doing shorter trains this may be accurate, remember the longer the train the longer the charge rate.

Thanks! I'll use 5psi.

I read in a manual that charging a "dry" train, with the train brake in the Release position (main reservoir connected directly to the brake pipe instead of going through the feed valve) could take up to 7 minutes per car on a long train! Assuming a typical 70psi in the auxiliary reservoirs, that would be like 10psi per minute, or 0.167psi per second!! The brake pipe needle would seem to take forever to rise. But I suppose they must be referring to a very long train.

The recharge rate only seems to affect the pressure in the brake pipe. The pressure in the main reservoir always seems to stay at its maximum, as if the compressor were always able to keep up with the rate at which the MR feeds the brake pipe. Is that right?

Also, I still can't find a way to simulate bail off. I read in this (fantastic!) document - http://railtown.team.parks.ca.gov/volunteers/Document%20Library20/1/ABTH%20Manual%20Railtown.pdf - that the most typical train brake system on a steam locomotive is the 6-ET, which luckily is the one I happen to have modelled.
The 6-ET has an independent brake valve (the S-6) with five positions - release, running, lap, slow application and quick application. The first (corresponding to bail off) and last are spring loaded - release will return to running if you let go, and quick application will return to slow application. However, RW doesn't model those positions. Sadly, it only allows Release (releases the brakes but not to lower than the train brake cylinder pressure, which is very odd) and Direct (applies the brakes).

[BNSFdude]

Compressors are set to come on whenever the MR drops below whatever pressure. Like on our SW1, it'll kick on at 125PSI.

[FourEightFour]

The recharge rate only seems to affect the pressure in the brake pipe. The pressure in the main reservoir always seems to stay at its maximum, as if the compressor were always able to keep up with the rate at which the MR feeds the brake pipe. Is that right?

No it is not, however, I believe this is a problem with railworks, as you cannot define a power rating on steam engines, and you cannot "pee away" your air.

Also, I still can't find a way to simulate bail off. I read in this (fantastic!) document - http://railtown.team.parks.ca.gov/volunteers/Document%20Library20/1/ABTH%20Manual%20Railtown.pdf - that the most typical train brake system on a steam locomotive is the 6-ET, which luckily is the one I happen to have modelled.
The 6-ET has an independent brake valve (the S-6) with five positions - release, running, lap, slow application and quick application. The first (corresponding to bail off) and last are spring loaded - release will return to running if you let go, and quick application will return to slow application. However, RW doesn't model those positions. Sadly, it only allows Release (releases the brakes but not to lower than the train brake cylinder pressure, which is very odd) and Direct (applies the brakes).

One of my chief complaints about railworks is that there is no bail off feature.

[mrennie]

I've been doing some more research in tractive force and horsepower.

I found this very useful link containing "Union Pacific Steam Locomotive Notes": http://utahrails.net/steam/steam-notes.php#horsepower

There's one part that says:

Tractive Force and Horsepower

From The Streamliner, Volume 2, Number 4, page 28

Formula for converting tractive force to horsepower at the rails (both steam and diesel locomotives).

(tractive force in pounds) x (speed in miles per hour) / 375 = (horsepower at the rails)

(drawbar pull in pounds) x (speed in miles per hour) / 375 = (drawbar horsepower)

(tractive force in pounds) x (speed in feet per minute) / 33000 = (horsepower)

For steam locomotives:

(0.85 boiler pressure in pounds) x (cylinder diameter in inches, squared) x (stroke in inches) / (driver diameter in inches) = (tractive force in pounds)

That last one I already knew about, but not the others. As I mentioned earlier, the Consolidation's T.E. came out at 34,841lbs. Also, I've already made a "TractiveEffortLinearVSSpeed" spreadsheet with a curve that is as close as possible to one I have in a book dealing with the evolution of North American steam locomotives, which has curves for various wheel arrangements (so I tried to get my curve to be close to the one for a 2-8-0). So, that curve gives the % of starting T.E. that we have at different speeds. To get the max power (at the rails) in HP, I plotted another curve with the power computed as :

Power = ((starting T.E.)x(percentage of T.E. at a given speed)x(speed))/375

The results are:

Speed fraction of T.E. Power at rails
0 1.000 452
5 0.970 839
10 0.900 1098
15 0.785 1184
20 0.635 1166
25 0.500 1113
30 0.398 1077
35 0.333 1041
40 0.279 1020
45 0.243 1040
50 0.223 1128

With that, I get that my "Max power" in the engine simulation blueprint should be 1184.

For Max force, I looked at the engine simulation blueprint for the Kuju Black 5. It has Max power = 1286 and Max force = 25.455. So, for the Consolidation, I calculated it as:

Max force = (1184/1286)*25.455 = 23.436.

Now I'll have to repeat that test run out of Altoona.

[ozinoz]

You know what they say - if you don't stop playing with it, you will go blind

You need to let your baby go now, otherwise we are never going to get it

Have to admire your dedication to accuracy though...





G

[mrennie]

You know what they say - if you don't stop playing with it, you will go blind

You need to let your baby go now, otherwise we are never going to get it

Have to admire your dedication to accuracy though...





G

RSC have had a beta version of it for a week but they still haven't "deployed" it via Steam to the beta testers. It has something to do with all these changes going on with Steam, I suppose. In the meantime, I'm taking advantage of the delay to carry on testing and tweaking. The thing is, I'm worried that if something isn't right, someone, somewhere, will spot it and complain, and I want the Connie to be as near perfect as I can make it. But ... as soon as Matt tells me the "deployment guys" are ready for it, I'll draw a line under this project and start the preparations for UP FEF-3 #844

Thanks for the moral support Grant, it's really appreciated



Mike

[ozinoz]

That really will be icing on the cake for Sherman Hill

[bpetit]

This has been needed for so so so long, if you are doing this it will be the biggest thing to hit RW since RW hit RW

SERIOUSLY THOUGH!!!

You know its going to be after the GN P2 right?

[BNSFdude]

He's mainly waiting for me to get the blueprints from GNRHS. I'm waiting for GNRHS to send them to me!

[mrennie]

He's mainly waiting for me to get the blueprints from GNRHS. I'm waiting for GNRHS to send them to me!

That's right, I'll be doing both in parallel. Shouldn't be a problem now that I've got my processes worked out.

The FEF-3 drawings will probably take 3 to 4 weeks to arrive.