As one who comprehensively tested the code as it was developed, I have but one thing to say with regard to data input. Where the real world sizes are known adhere to them, do not make changes. The code will take those figures and give an output that should be very close to the real deal in terms of steam production and usage, power output at the wheel and drawbar.
So far I have found some adjustments to be useful, representing the fact that some steam locomotives were less efficient than others.
(1) ORTSBoilerEvaporationRate ( ) - in some cases, boilers could not reach the maximum output calculated by ORTS because of factors such as draughting (improved by redesigned blast pipe, double chimney, giesel ejector..) or for other reasons related to length of tubes compared to diameter, free gas area, etc. Where boiler output has been measured I fell this adjustment is justified.
(2) ORTSCylinderInitialPressureDrop( ) - represents the valve gear setting.
I have used this in the Princess so that work achieved at a given cut off is realistic - otherwise I might have to haul trains with 5% cut off where in real life 20% was used for the same speed/power. I would also use this to represent short travel valves on older locomotives, where steam supply to the cylinders got choked off at higher speeds. [MR 2P 4-4-0 Mean Effective Pressure at 300 rpm was 30% of that available on starting compared to 60% for a rebuilt Royal Scot.]
(3) ORTSBurnRate( ) - should help to give a more accurate coal consumption, however it is not easy to get information on this. I tried to make an estimate for the Jubilee based on pounds of water evaporated per pound of coal in road test reports. When I later found that one of this class had been laboratory tested I found that my original estimate was not correct.
The one thing that the code does not do is work very well with an Fcalc calculated Davis C value. What one needs there is an existing resistance curve for an item of rolling stock and using one of them behind an engine, record the values at 10 mph intervals, then see how that plots against the known curve. Adjust the C value if the curve is wrong and retest. Once that is done, all stock of a similar type can use the same Davis figures. Then with a known set of figures and a train to match set up the loco with the initial Fcalc figures and run the train to its maximum attainable speed. See if the complete train can match the published figures. If the figures achieved are lower than published adjust the loco Davis C downwards and try again. Keep going until the figures achieved match the known ones. The loco will then perform accurately in all circumstances, lighter trains will give better fuel figures, heavier ones will give higher fuel consumption for the same distance and run at a slower speed due to the extra resistance.
This is where most of us will need help. Perhaps someone with a better understanding of railway physics and engineering could trawl relevant sources and post some guideline figures (in the correct units for ORTS!) that will get us started and help things move in the correct direction.
Since the majority of things that I model are late 19th and early 20th century I doubt that there is much data available so will need to know how to make reasonable estimates from data that is available.
FCalc is easy to use for any rolling stock - would it be possible to make a similar C value estimator that would be of more general value for ORTS?
As the C value for locomotives (or leading vehicles) is very much greater than that for other vehicles, might we accept FCalc values for other vehicles as being acceptable and then concentrate on adjusting the locomotive values?
