by dtrainBNSF1 » Tue Sep 12, 2017 11:48 am
Dear friends,
It's been a LONG time since I posted anything related to steam locomotive mods. I've been without a computer for a while but now I've got a new one and I am pleased to announce that I am back to my regular shenanigans of tinkering around with steam engines for TS2017.
During the nearly year away from Train Simulator and modding I used my pad to do some research on steam locomotive design and power computation, including how to properly calculate drawbar horsepower, indicated (cylinder) horsepower, tractive effort, speed, and a better method of estimating a boiler's evaporation rate. To illustrate the difference in my old method and the new method I've found let's look at one of my first mods on the site - the Big Boy mod. According to sources the highest rate of evaporation for a steam locomotive boiler ever recorded was at the Altoona Test Plant with a Q2 4-4-6-4 with about 137000lbs/hr, and what was recorded at the Test Plant had to be taken with a grain of salt because these figures were impossible to reproduce on the road in day-to-day operation due to the fact that the engines there were pushed to their absolute limit and were expertly handled far beyond the abilities of regular drivers. What is the evaporation rate of my Big Boy mods? 168,000+ lbs/hr! WAY to high to be believable. In real life the Big Boys were likely to have an evaporation rate of 120-125000lbs/hr.
I'm also planning on reworking the weights of my locomotives and tenders to reflect them when empty. I regularly use figures from steamlocomotive.com for the weights, but the loco weight is in working order and the tender weights are when full of coal and water. Given that in the associated bin files there are places for capacity and in the sim file there's a space for water mass my previous mods were probably a bit heavier than in real life which makes a difference performance-wise as the locomotive has to move not only the tonnage it's pulling but also its own weight.
I'm also changing the way the mod interacts with the tevsspeed and the tevscutoff files to something similar I saw when I looked at the Jubilee locomotive. In the Jubilee locomotive the tevsspeed file values are all "1". The reduction to tractive effort due to speed was all taken account for in the tevscutoff file which is way longer than any other tevscutoff file I've seen in other locomotive for Train Simulator. This is similar to the FEF-3 where most of the tractive effort reductions are done in the tevscutoff file, and when you think about it it makes sense. The cylinders on a steam locomotive take in steam based on the reverser setting. When the reverser is at full forward or full reverse the cylinder gets filled with a large amount of steam and the expansion and pressure of this steam is what pushes the pistons and turns the driving wheel. The cylinders are more than happy to take large amounts of steam, but due to the amount of pressure in the cylinder it's not going to move very fast. With lower reverser settings there's less steam in the cylinder which means more room to expand and less pressure which means the piston can move faster, however because there is less steam in the cylinder there is also less force pushing against the piston and therefore less force being transmitted to the drive wheels and thus less tractive effort. At least that's how I think of it anyway. I'm no expert, so I might be a bit off.
Anyhow my method takes into account wheel diameter, evaporation rate, cylinder volume, number of cylinders, speed in rpm, and whether or not the locomotive has such modern innovations as feedwater heater to produce tractive effort up to 250rpm. From 250rpm onwards a second method is used which takes into account a steam locomotive's mean effective pressure at various speeds. To illustrate, here is a theoretical set of tractive effort and drawbar horsepower values of the 700 from 50rpm to 250rpm (given that the SP&S 700 has a maximum drawbar pull of 5000hp):
SP&S 700
Theoretical Evaporation: 90189.98525776769
50rpm(11.44791666666667mph)=69756; 2129.495666666667hp
15mph=69756;2790.24hp
16.78509146427353mph=69756;3122.295573818305hp
17mph=69541.61252356774;3152.553101068404hp
20mph=66548.88621270886;3549.273931344472hp
25mph=61561.00902794404;4104.067268529603hp
30mph=56573.13184317923;4525.850547454338hp
35mph=51585.25465841441;4814.623768118678hp
40mph=46597.3774736496;4970.386930522624hp
43mph=43604.6511627907;5000hp
45mph=41609.50028888478;4993.140034666174hp
50mph=36621.62310411997;4882.883080549329hp
55mph=31633.74591935515;4639.616068172089hp
250rpm(≈57.24mph)=29399.59259701259;4487.521147794005hp
So plenty to do with mods and to start things off I'm going to release a mod for the K4s which I talked about for a while and then my computer died so I couldn't release it.
In short I'm back and I'm ready to go back to work on mods. I'm working on my Masters Degree right now so serious work with Train Simulator is probably going to have to wait until the weekend regularly.
If what you've done is stupid but it works, then it really isn't that stupid at all.
David Letterman
The only stupid question is the question that is never asked.
Ramon Bautista