ORTS Standard Engine Files

[R. Steele]

I'm away from home, but I do have RPM data for early dash 8s (which should work for Super 7s, too). I could look through some of the other manuals I've found, too

Whenever you can, that would be excellent, thanks so much Travis. Some of it is in the manuals, but not the RPM increases from notch to notch, that's what is hard to find. Regards, Gerry

[derekmorton]

Hi Gerry,

I have always worked out Adhesion factor with CTE rather than STE.
Any reason you use STE?
I wonder what Bob uses?

[=FI=Ghost]

Thank you very, very much!

[R. Steele]

Hi Gerry,

I have always worked out Adhesion factor with CTE rather than STE.
Any reason you use STE?
I wonder what Bob uses?

This thread, Bob's posts >> https://www.trainsim.com/vbts/showth...91#post1947391

some excerpts:

If you know the weight of the unit (I could not list that as some units vary widely (for example with the SD40-2, Milwaukee had some as light as 356,800 pounds, while Burlington Northern had some that weighed 419,500 pounds)), you can multiply the adhesion X weight to get starting tractive effort. In the SD40-2 example, The Milwaukee unit would have about 94,550 pounds of starting tractive effort, while the BN unit would have about 111,168 pounds of STE. They both would have the same CTE so above 11 mph the heavy unit doesn't do more, and it adds to the consist weight, but it will start a heavier train. The adhesion values assume good quality clean rail in dry weather, thus these are the optimum, weather and debris will degrade the adhesion. You will note, my data is internally consistent.

If you know what a locomotive weighs, then you get the starting tractive effort by multiplying the weight by the adhesion, for example if the locomotive weighs 429,000 pounds and has a nominal adhesion of 35%, then it's starting tractive effort is 429,000 * 0.35 = 150,150pounds of force = 667.9kN of starting tractive effort. It can only stay in that condition a few moments, but it is enough to start a train rolling.

my underlining.

also, verification from another source: https://www.republiclocomotive.com/a...-traction.html
excerpt:

The tractive effort of a locomotive (whether AC or DC) is defined by the equations:

Tractive effort = Weight on drivers x Adhesion
Adhesion = Coefficient of friction x Locomotive adhesion variable

The friction coefficient between wheel and rail is usually in the range of .40 to .45 for relatively clean, dry rail in reasonable condition and is essentially the same for all locomotives. The locomotive adhesion variable represents the ability of the locomotive to convert the available friction into usable friction at the wheel rail interface. It varies dramatically from about .45 for old DC units to about .90 for modern AC units. This variable incorporates many factors including electrical design, control systems, truck type and wheel conditions.

I've tried to track down, in test papers, the method by which the "locomotive adhesion variable" is calculated or arrived at....have not had much success doing that. Just curiosity, because Bob's published adhesion factors are so accurate ( and consistent ) that you really don't need to go much further.

Just to continue the conversation about tractive effort a little further for anyone who's interested.
Once the STE is determined and the CTE is known ( CTE is a function of the traction motors ) then tractive curves can be developed.
In the case of OR - - the curves take the form of a "curve set" -- the "ORTSMaxTractiveCurves" there are different ways to calculate these.

I prefer to use the following equation ( thanks to Derek for finding this page for me )

http://128.173.204.63/courses/cee3604/cee3604_pub/rail_resistance.pdf

T = 2650(nP/V)

T is tractive effort in newtons
2650 ( constant which correctly converts units of equation to newtons )
n represents the efficiency of the locomotive in converting output power at the shaft to tractive power
P is the Horsepower of the locomotive - measured at the shaft of the diesel engine
V is the velocity

So far, I'm still trying to learn how to calculate the CTE from the traction motors parameters...this is proving to be a very step learning curve for me. Anyone having knowledge of that .... please let me know.
Regards, Gerry