Bill's Fock's spreadsheet is based on in game testing of several locos probably back in tS09 days. But mostly based on empirical data. His R parameter is used to set the maximum HP output of the locomotive. I've explained this in more detail in other posts but essentially it sets the speed at which the max hp is produced. So 0.6 would be 60% of the loco's top speed which he assumes to be speed in mph is equal to the drive wheel diameter in inches - an old rule of thumb. I have my own spreadsheets based mostly on therory - simplified mechanics and thermodynamics. Bill and I both found Trainz espec produce too much power if you blindly input the actual engine characteristics and dimensions. We both use a reduced swept cylinder volume to reduce power output of the locos
Bill's spreadsheet provides an easy means to come up with an espec but it needs to be followed by some or alot of in-game testing to tweek it.
I wrote a reply to this thread several days ago and since it's continued along this far I guess I let you have it here:
Hello, all.
I've been running some British steam locomotives (most notably from Skipper1945 and the Potteries Loop Line crew) and i've noticed one big issue: when starting off, whether the cutoff is at 15% or 75% or anywhere in between, i get a drop in boiler pressure of about 40-50 psi. I don't know if this is an isolated issue, but seeing as this happens to all of the locomotives i've driven recently, each with differing enginespecs, i can't help but think that it's not the enginespecs causing the problem.
I've driven steam locomotives in both MSTS and Railworks, and neither of those games have this issue. I've also tried a variety of adjustments, like starting with a lower cutoff and a lower regulator setting, or starting with a low cutoff and a high regulator setting; nothing works. I always have a large boiler pressure that ends up never getting back to where it started, thus deeming steam locomotives inoperable in most cases. I even had one time, driving a Fowler 4F, where as soon as i opened the regulator at all, the boiler pressure steadily dropped without stopping, until i was down to 1 psi.
Does anyone know of a fix for this issue? I'd prefer not to have to go into each and every engine to edit it's enginespec, but if that is the problem then i guess i have to. If not, has anyone else seen this and/or fixed it?
IMO it is an espec problem. Opening the throttle should not cause a drastic drop in pressure. Especially if the loco is near operating temp and has water in the boiler.
I don't experience this with the especs I develop. I usually make my own espec for every steam loco I like to run (and can open and edit the loco's config) from Peter P-M's DHR and SRRL 2 ft ng locos to Ben Neals C&O H8 and USRA 2-8-8-2. I spend the most time in Ben's EBT 2-8-2 heavy class (reskinned for nos 16-18). In my driving experience in Trainz, I get fairly realistic power output, safety valve operation, fuel consumption and boiler pressure simulation.
But I've found you won't get it by just inputting the locos listed characteristics. Clearly IMO there is something wrong with the steam simulation in the game. This is their 2+ try at it and they didn't get it right yet. I base my espec mainly on 1st principles using fairly simple calculations of mechanics and thermodynamics. There has to be an energy balance of work preformed with heat energy released from the fuel based on the efficiencies I assign. Water evaporated in the boiler has to balance with steam consumed in the cylinders.
The enthalpy of the steam is a known quantity vs pressure for saturated steam or pressure and temperature for superheated steam, so the energy transfer and steam flow are tied together. I think you'll find steam flows in most especs are kind of a guessed at quantity. I calculate the flow required to deliver the necessary energy to the cylinders and then design the boiler (within the limitations of the Trainz simulation) to supply it.
From a lot of testing I know that the Trainz simulation produces way to much power and IMO the best way to work around it is to design a steam loco that is about 50 - 60% the size of the real loco. Another trainzer Bill Fock aka Billegulla, who has since passed on and missed, came to the same conclusion. He didn't take it as far as I do in designing the whole boiler but his range of reduction in cylinder size was even greater than mine. Accept it or not the especs work and give a good simulation for just about everything except water consumption. Which has it's own problems anyhow.
Bob Pearson
PS. Initially the boiler has a specified pressure, temperature, water volume and steam mass as determined by parameters in the espec. All volume downstream of the throttle valve ie. the piping, reservoir if one, steam chest, valves and cylinders are at atmospheric pressure. When you open the throttle initially steam flows to fill this path up to the cylinders until equilibrium is reached and flow stops. Steam only flows into the cylinders when the reverser lever is moved from it's 0 position (forward or reverse).
Just based on comparing volume of the boiler volume above the water and volume down stream of the throttle valve you would not expect a large drop in pressure. A typical 2 cylinder espec should have about 2 to 2.2 times the swept volume of 1 cylinder as the volume filled when the throttle only is opened. A typical boiler at 70% full on the gauge probably has about 87% of the boiler volume filled with water. So just 13% is left for steam. That's still around 4 or 5 times the volume of steam that's lost to the flow when you open the throttle the 1st time. At least that's what it should be and it's typical for most of my especs.
Assuming the 4 to 1 ratio and no temp change: P1/P0 = V0/V1 = 4/(4+1) = 4/5 = 0.8 for this case and you get 20% drop max. There may be some more due to condensation of saturated steam in the external piping and chest/valves, but with superheated steam this is usually little or none. However as the pressure drops new stream will be evaporated even if you dump the fire at that instance (fireless steam loco is the best example of this). Only the latent heat for change of state is required and it is pulled from the large quantity of water at the now elevated temp for the current steam pressure. Initially in the boiler the water and steam are at same temp. A final equilibrium condition is reached with the boiler at a slightly lower water temp and corresponding steam pressure. So overall I'd expect to see some but not much drop in BP.
If you don't see this happening then the espec is not set up correctly.
There a few anomolies in the Trainz steam simulation that can compound the problem. In the espec you can force more stream in boiler than would normally exist at a given temperature for saturated conditions. In game you can force water into the boiler and raise the pressure while it is sitting still but when running it it appears to decrease boiler temperature and decreases the pressure. It's not apparent to me that the change in volume of liquid water in the boiler vs temperature is actually simulated in the game. And we have no control over the temperature of the water being forced into the boiler whether by pumps with or without feedwater heaters or injectors with live or exhaust steam. Is that appropriate for a simulation like this?
They say significant changes haven't been made in the steam physics simulation from TS10 thru TANE but I have not done any extensive test in TANE, TANE sp1 or sp2.
@Zec
Essentially Trainz doesn't properly model loss of steam when either the regulator or safety valves are closed. Hence the boiler pressure doesn't drop overly quickly when the fire is cold (it generally will be when the session starts, as the loco is at idle).
It can do a fair job if you get the "boiler-heat-loss" parameter right. Unfortunately there is little info/documentation provided by the people that developed the whole thing. I'd think it should be related to heat loss per unit surface area per unit time. Something like Watts/sq meter (btu/sqft/hr in imperial units). Except we don't input boiler surface areas. But clearly it does vary with boiler size in the game. I now base it on boiler volume using V x 0.2015 and that's simply based on empirical testing. I don't see how they could design the simulation and not know what happens at each step of the process. They should know what each param represents and valid ranges for them IMHO.
Back to Today:
Alright, i look forward to the updates. Thanks for your help.
EDIT: So i took 2995valiant's advice and set the blower up 1 notch before moving...and voila, no loss of pressure! I really can't believe it was that simple...whatever, i'm thankful to have found a fix.
I don't know of any real locos that routinely run with the blower on. But I'm sure some where some time some loco did it. Yes to build up pressure while sitting idle. Or with locos that don't steam well they might need a bit of help but these are exceptions.
Espec needs to be fixed.
Regards,
Bob
