[Gehe]

Hi All,


in the last days I did some tests of steam locos and used of Course the steam F5 HUD. As an Outcome I do not understand some of the values.
Since I did not find a detailed explanation of the F5 HUD in the documentation I start this topic.

HUD values:
In the lowest part of the HUD F5 Steam the "performance" part the max IHP is shown which looks like to be derived from the evaporation area multiplied with the steam production per sq inch or sqm.
Additionally there is IND (IHP?) given, TE (traffic effort)and drawbar which I figured out to be the force at the drawbar of the tender.

In the upper part also a power value is shown which looks like to be the same i.e. the IND.

I expected that TE is the "indicated" force calculated from IND and based on the .eng parameters and the position of the reverser and the throttle.


In my Tests I do not understand the follwoing behaviour:
If you start the train and you reach a power level beyond the calculated max IHP, the IND indicator sticks to the max values and does not show any larger values, like the power values in the upper part of the HUD.
Unlike to this the TE indicator gives larger values. But not corresponding to the drawbar indicator which shows values corresponding to the max IHP. It shows the force derived from max IHP minus friction of the loco+tender.
So I did some further trials:
If you are at constant speed at a power level beyond max IHP according to TE that means the TE value converted back into power is larger than Max IHP and you put the reverser full forward resulting in excessive steam usage I expected two things: To exhaust the boiler which happened and some acceleration which did not happen according to the track monitor.

So I have the question how does Open Rails calculate the Forces and power values? Is the power of the loco limited to max IHP? This would be strange since you should be able to use the energy content of the boiler for increased short time performance.
Therefore my questioin: Do I completely misunderstand the values given in the HUD?

Regards

Gehe

[copperpen]

With full forward or backward reverser steam usage reaches a point where the cylinders are unable to move more steam and so are unable to accelerate the train any faster. Max Ihp is an internal calculation and OR will never display figures beyond that, unless you set the Max Ihp in the eng file, in which casef the displayed figure will run up to your declared max, but only if the engine is physically capable of reaching that figure.

TE is the maximum force applied through the driving wheels to the rails expressed in pound/foot or the metric equivalent. Drawbar HP is the amount of power needed to haul the train behind the engine..

As the train gains speed, the IHP will rise and the TE will fall, total locomotive power is limited to the max IHP figure. Eventually a heavy train will reach a speed where resistance equals power output and it will go no faster, regardless of the max ihp figure.

When a steam locomotive is running at speed, the reverser will be down to 25% or lower for passenger trains, and within limits of steam usage you can use more of the energy stored in the boiler for short periods, such as maintaining speed over a short grade.

[Gehe]

Thanks for the fast Response. In the meantime I found the Physics section on the OR page which answers a lot of Questions.

Just one Point:
In the document the parameter ORTSBoilerEvaporationRate is related to the grate area.
I guess this should be the evaporation area because a steam production of 10-15 lb/sqft fits well to the evaporation area


Regards
Gehe

[scottb613]

Gehe, on 06 February 2020 - 12:44 PM, said:

Thanks for the fast Response. In the meantime I found the Physics section on the OR page which answers a lot of Questions.

Just one Point:
In the document the parameter ORTSBoilerEvaporationRate is related to the grate area.
I guess this should be the evaporation area because a steam production of 10-15 lb/sqft fits well to the evaporation area


Regards
Gehe

Hi Gehe,

As a fellow steam aficionado - welcome...

For he most current and detailed description of ORTS physics - check Peter’s fantastic site as it contains a wealth information and he’s the developer who’s created much of what we have today... ORTS has the most realistic steam physics I’ve ever come across...

http://www.coalstone...com.au/physics/

Regards,
Scott