[PerryPlatypus]

I have been running a number of tests to try to replicate correct adhesion on my Mullan Pass route with AC traction diesels, particularly the SD70ACe as a starting base.

I have been able to adjust adhesion to nearly-perfectly follow adhesin under dry rail conditions.
For the SD70ACe:
Weight= 408,000 lbs
Max Tractive Effort: 191,000 lbs
Thus, adhesion at 0 MPH: 46.8%
Continuous Tractive Effort at 12 MPH: 157,000 lbs
Thus, adhesion at 12 MPH is 38.5%
Using Excel, I left the C and D Curtius-Kniffler values as default, and changed A and B until I could get the correct adhesion percentages at both 0 and 12 MPH. This was achieved using the following Curtius-Kniffler parameters: 16, 52.2, 0.161, 0.7

Now this results in extremely realistic performance in dry rail. The problem is when it comes to rain, snow, or fog conditions...

It seems that these factors are reducing the adhesion way for than is realistic. For example, when snowing and I have the option checked to adjust adhesion in proportion to precipitation or fog, I lose more than half of adhesion, making it nearly impossible to start moving on a grade.

I did some research online and did find adhesion coefficients relatively close to those being used in OR. Here were my findings for adhesion adjustment factors:
Dry rail: 100%
Clear+Sand: 110+% (seems that OR is using 150%?)
Rain: 67%
Rain+Sand: 83.3%
Snow: 33%
Snow+Sand: 0.15 50%

But in real life, the overall adhesion for the train certainly does not drop to 50% of dry rail (even when using sand) when snowing. I have watched heavy unit grain and coal trains climbing the 2.2% of Mullan Pass in the middle of a blizzard in real life, and they may have one additional engine added compared to dry conditions, or they may have no additional engines, and they are still able to climb the grade at almost the same speed as in dry weather.

So what is the difference?

The snow adhesion coefficient in OR is based on snow being on the surface of the rail. However, in reality, this will only affect the first several axles on the train. As more wheels roll over the rail, the snow will quickly get shoved off the rail. Theoretically, this means that the further back each engine is in the consist, the adhesion coefficient should improve, re-approaching dry rail conditions over the first few axles. After snow has been removed by the first few axles, adhesion would reach that of simply a slightly moist rail. The same would apply for snow conditions: "Rain" adhesion should only apply to the first few axles of the train, and then drop to an improved "moist" adhesion coefficient for the rest of the train. Below are my suggestions. Obviously for lower intensities of snow, rain, or fog, the adhesion should be linearly interpolated between dry conditions and the condition in question.

When Snow falling, max intensity:
Adhesion for first few axles (first locomotive for simplicity): 40%, or use current Open Rails value. Sanding will improve to overall 60% adhesion.
After first locomotive: 90% adhesion due to mild moisture condition. Sanding will improve to 100% adhesion.

When raining, max intensity:
Adhesion for first locomotive: 67%. Sanding will improve to 83%.
After first locomotive: 90% adhesion due to mild moisture. Sanding will improve to 100% adhesion.

When foggy, max intensity
Adhesion for first locomotive: 67%. Sanding will improve to 83%.
After first locomotive: 90% adhesion due to mild moisture. Sanding will improve to 100% adhesion.

Now this brings me to another suggestion: "Icy" conditions should be separated from all of this. Rain, fog, and snow can all exist without ice accumulating on the rail. For ice on the rail, the slippery condition (and resulting drop in adhesion) will not dissipate after the passing of the first locomotive. The adhesion settings that are currently being used in OR, where the adhesion stays low for the entire train, much more accurately represent icy conditions. Ice conditions ought to be added as an additional menu option next to precipitation (say None, Medium, Severe ice conditions) For better control, a Weather Change variable could be added to account for icy conditions, called such as ORTSIceIntensity, variable from 0.0 as no ice to 1.0 as severe ice. It is reasonable to use the current OR values for snow adhesion (or even a slightly lower coefficient) to replicate maximum intensity ice conditions.

[engmod]

Be aware that ORTS does not do AC tractive effort yet.

It only does DC traction curves.

[PerryPlatypus]

engmod, on 01 January 2018 - 07:31 PM, said:

Be aware that ORTS does not do AC tractive effort yet.

It only does DC traction curves.

Could you elaborate on this? I am not sure what the difference you are talking about is between the tractive effort curves. The Curtius-Kniffler values I listed at the start of my post seem to accurately replicate the adhesion of the SD70ACe. For tractive effort, I just created ORTSMaxTractiveForceCurve values.

[engmod]

I don't know how it relates, but ORTS does not honour AC traction.
I have bug reports in that have not been actioned.

[R H Steele]

Reading for beginners...yep that's me, third time through, gotta find more reference material.
http://cs.trains.com...1/t/112679.aspx

Why were DC traction motors modeled first?...more of them used throughout railroad history, AC being a recent innovation thanks to solid state?
Is there any difference between the two with respect to traction delivered at the railhead?
..oh and...I've always known
Telsa was right. http://www.elvastower.com/forums/public/style_emoticons/default/derisive.gif http://www.elvastower.com/forums/public/style_emoticons/default/dance.gif

Interesting stuff. http://www.elvastower.com/forums/public/style_emoticons/default/sign_thank_you.gifhttp://www.elvastower.com/forums/public/style_emoticons/default/cool3.gif

[engmod]

>Is there any difference between the two with respect to traction delivered at the railhead?

Yes, AC traction can do what is called "creep"

The maximum traction available is at 11% slip.
AC machines can do this as they are frequency controlled, and they all have "ground radar" to measure speed very accurately.

The 'creep' is currently NOT modeled, so AC machines can only develop as much tractive effort as an equivalent DC engine. ie one with the same tractive effort.

[ErickC]

Wheel creep predates AC traction on EMD locomotives and was part of the Super Series system used on the SD50 and SD60.

[engmod]

The first AC traction was in 1971, DE2500 DB202

DC creep is rather different from the creep that AC machines can develop.

DC machines CANNOT do 11% slip.

[copperpen]

Just a question. When deciding on the Curtius-Kniffler what were your adhesion sliders set to on the Experimental page?. The default is to use MSTS levels. I always have the two sliders at 100% and 0% variation.

[ErickC]

engmod, on 02 January 2018 - 01:12 AM, said:

The first AC traction was in 1971, DE2500 DB202

DC creep is rather different from the creep that AC machines can develop.

DC machines CANNOT do 11% slip.

EMD SD50 Operator Manual said:

"Super Series adhesion control allows the SD50 (and GP50) wheels to "creep" or turn slightly faster than true ground speed during "hard pull" situations such as climbing hills with maximum tonnage or starting a train. The SD50 wheels, for example, may develop from 5 to 15 percent creep. When a 10 percent wheel creep exists, for example, the engine's true ground speed may be 10 MPH but the wheels may be turning at 11 MPH. (The speed indicator on SD50 and GP50 engines shows true ground speed based on the radar speed sensor.)"

AC traction is superior and offers many advantages over DC, but 11% wheel creep is not one of them.