[engmod]

At least we agree on the major items.

From plainsman

Beyond what has already been said, there are other reasons AC traction motors outperform DC motors.
AC traction motors are three phase motors. In other words, they have 3 peak outputs for each rotation. What this means in a practical sense is that they will do about 1.73 times more work than a DC motor if fed the same power.
With inverters needed for AC units are about 96% or better efficient in practice. They may drop below this in fixed frequency conditions, but in practice computers maintain near frequency synch under locomotive operating conditions.
DC traction motors have a transmission efficiency that is near 90% in the latest SD70M-2 and GEVO DC units. The ACe EMD AC units can better 93.5% transmission efficiency and GEVO is right at 93.5%.
So for say 4,300 HP generated by the diesel engine,
DC will put
4300 x 0.897(transmission efficiency) = (3857 HP) at the rail and do 1.0 times the work.
AC will put
4300 x 0.98(average inverter loss) x 0.936(transmission efficiency) = (3944 HP) at rail and do 1.73 times the work.
Since AC motors are 3 phase and have frequency synchronized by computer, they can be much more precisely controled than DC. This results in better adhesion as Derek mentioned above. A SD70ACe under IDEAL conditions will get as much as 46.5% adhesion. A SD70M-2 under the same identical conditions would only get about 34-35% adhesion. Thhis is what controls the starting tractive effort. The STE will be the adhesion times the weight of the locomotive. This will vary under different conditions. On greasy wet rail, it is a lot less than on clean dry rail. The computer controls power to control wheelslip so that max

tractive effort is achieved (ground speed is measured and compared to wheel rotation speed such that only about 11% wheelslip

is allowed). Since the AC motors are much better controled and since they have a smoother power curve (3 phase), they get better adhesion.
AC motors can in practice operate down to very slow continuous speeds at full throttle as mentioned above. Depending on gearing, some units may operate at almost 2 mph. DC designs would fry the motors at those speeds. In diesel electric locomotives, as speed drops, pull increases. Thus the max contiinuous tractive effort is much greater for an AC design with the same prime mover output, as compared to a DC design.
Hope this helps, and if you prefer the intensive math explanation ask?
Bob

[PerryPlatypus]

copperpen, on 02 January 2018 - 01:58 AM, said:

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.

I have been using exactly as you just said, 100% and 0% variation, this way the adhesion that the Curtius-Kniffler equation is calculating is exactly what I am actually getting in-game under dry rail conditions.

[R H Steele]

copperpen, on 02 January 2018 - 01:58 AM, said:

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.

To both copperpen & Sean
Question: Is the "Adhesion proportional to rain/snow/fog" box checked?
Checked - the level is very hard, Unchecked, the level is rated normal

[copperpen]

Yes I do have the proportional box checked. I do remember though that if any of the engines used in the consist have a lower adhesion rate than the rest, regardless of where it sits in the consist, it will slip first and force the rest to do the same unless rpm is reduced to below the slip threshold for that particular loco. I also feel that the adhesion in adverse weather conditions should be revisited and not assume that snow equals ice which I feel is the situation now. Snow is no worse than rain in normal conditions.

[ATW]

Interesting ORTS still has a ways to go in AC. Now I don't know why I created custom AC/DC Traction Curves, Axle loads an adhesion values as well as timings. DC representing Direct TE curves an AC representing alternating TE curves based on values of GE experienced settings told by AlKrug an other references.

I am glad this topic is here because I already have TE, wheelslip control, Throttle settings based on railroad specific readings, settings, fuel charts etc but I am trying to get the adhesion values squared away. While hearing from the actual engineers I work with, I keep hearing that the average Widecab EMD or older GE are not very good comfort performers at high speed where they vibrate or even have there speedometer vibrate at 50MPH an above a lot. I have settings that do the same but they only do it at low speeds an I am trying to get them to do it the faster they go that it happens only when adhesion exceeds 35%. I can have settings that lock the selected adhesion settings for majority of speeds, I just can't make the adhesion % creep up the faster it goes like I expect to find an keep experimenting.

My settings are Proportional to Rain/Snow/fog checked, Factor correction 100%, Factor Random Change 1% and Adhesion Moving Average set to 10. Still a work in progress it's pretty good, but something always has to come up in different projects, enthusiasm or requests an my away from ORTS in the personal work life.

I guess I need to stop procrastinating on releasing a beta. Modern NA locomotive testers can PM me if they are interested.

[R H Steele]

How does OR model Starting Tractive Effort? or does it?

[ATW]

It does an variables is possible. PM me.

[PerryPlatypus]

ATW, on 03 January 2018 - 06:44 PM, said:

It does an variables is possible. PM me.

I am actually very interested in this as well. I have wondered whether the tractive effort values used in an ORTSTractiveForceCurves table are the continuous or starting TE? How do we determine how much more starting TE is than continuous TE?

I hope that in the near future someone can gather together the working knowledge on tractive effort, adhesion, power, etc. and release a package of Open Rails ENG files of all common diesel locomotives to somewhere that all users can easily download from. This would be a massive step forward for Open Rails, since currently there are very few standard physics available...

Gerry, I have checked Adhesion proportional to rain/snow/fog, as even those this is rated as "Very Hard" this theoretically should be the most realistic setting, from what I can tell.

[engmod]

>How do we determine how much more starting TE is than continuous TE?

The hud gives information like that!!

[Hamza97]

https://www.youtube....h?v=bdLcipx37b8