[steamer_ctn]

I have come across another locomotive with an incorrectly specified MaxPower value. My current tests look for values that are missing, but in this instance there is a value, but it is only (2440W) 3hp.

I can put in a test to make sure that the MaxPower values is always greater then a certain value. What would be a reasonable value to set as the minimum? In other words what would be the smallest locomotive that anybody would hope to model?

Thanks

[railguy]

I would suggest a very minimum value of, say, 1 HP. The reason is that some models are set up as .eng files (for light cones, etc.) even though they are un-powered. Two examples are some Jordan Spreaders and Russell Snowplows. In prototype operation, these often have a control stand to control the locomotive(s) pushing them, but are themselves un-powered. Motorcars (speeders), hy-rail trucks, and other on-track equipment often have relatively low horsepower, as well.

[steamer_ctn]

railguy, on 16 December 2019 - 12:32 PM, said:

I would suggest a very minimum value of, say, 1 HP. The reason is that some models are set up as .eng files (for light cones, etc.) even though they are un-powered. Two examples are some Jordan Spreaders and Russell Snowplows. In prototype operation, these often have a control stand to control the locomotive(s) pushing them, but are themselves un-powered. Motorcars (speeders), hy-rail trucks, and other on-track equipment often have relatively low horsepower, as well.

Thanks for the comments.

I have instead decided to add a precautionary message rather then effect any changes. The user can then elect to make changes if necessary.

Thanks

[NickonWheels]

Hey guys, I just enter my words here...

I have something for you to check out, part of an include file for the SD40-2 complete with traction curves (just pictures because I can´t upload the whole file for some reason).


These are based on the include files uploaded by Gerry, who wrote they are public domain, so I modified them to 'I think' more realistic values.

If you now wondering how I got to these values... I just calculated them based on what I read on Wikipedia (again) and some own assumption on what would be most realistic on the matter. It´s rather sad traction curves does´nt work on electric locomotives, they need them too.

'THAT friction guy' Nick

[R H Steele]

From your traction table (Maximum traction = 140000lbs) you either have a SD40 that weighs as much as a DDA40x ( approx 528000lbs ) or an SD40 with an adhesion factor of 36.9% ---- am I missing something? Seriously, all this train physics is pretty much new stuff I'm learning, so maybe I've missed something.
It's good you're using my basic work to explore on your own, I hope more people do just the same thing. Regards, Gerry

[NickonWheels]

Thanks, Gerry

That is an SD40-2, which (I assume) weights 200 short tons or 400000 pounds and has an adhesion factor of 35%.
35% of 400000 is 140000, so that´s why. The formula behind this takes into account the speed as well as voltage limits, so the starting tractive effort at 50% throttle (or notch 4) is half of full throttle and so on...
The whole calculation is done with a rather complicated but very useful program I developed with my dad, which also puts out fuel consumption and engine power at the different notches.

Don´t be afraid of physics, ORTS is afraid of them too...

Nick

[R H Steele]

NickonWheels, on 17 December 2019 - 11:55 AM, said:

Thanks, Gerry

That is an SD40-2, which (I assume) weights 200 short tons or 400000 pounds and has an adhesion factor of 35%.
35% of 400000 is 140000, so that´s why. The formula behind this takes into account the speed as well as voltage limits, so the starting tractive effort at 50% throttle (or notch 4) is half of full throttle and so on...
The whole calculation is done with a rather complicated but very useful program I developed with my dad, which also puts out fuel consumption and engine power at the different notches.

Don´t be afraid of physics, ORTS is afraid of them too...

Nick

My concern is that your initial assumptions regarding the mass and/or adhesion factor for the SD40-2 are incorrect-- too high, therefore everything that follows is subject to question.
Here are my reference points for Mass and Adhesion factors:
Bob Boudoin ( most recent values used for OR physics ): SD40-2 84.0% ( power transmission efficiency -- Generator/Alternator input HP to Rail Hp ) 3000HP 26.5% ( adhesion factor ) 369.6kNCTE @11.1mph Mass: 390218 ( 177t or 195t-us )
EMD SD40-2 Manual: approx. weight on wheels: 368,000lbs
Derek Morton: Mass 390000lbs; 103050 ste = 26.4% adhesion factor

So given all the above, your weight seems a little high but still in the ballpark of operational weights.

What is your source for the adhesion factor of 35%?-- which does seem too high for a DC locomotive...but if you have a reliable source...I ask because I'm working on version 2 of the Std_eng files and always looking for good source material.... and question #2, can you share your calculations?
Regards, Gerry

[steamer_ctn]

I don't know whether this is a helpful reference or not for the SD40-2. Others can comment on the accuracy of the information on the site.

The challenge, as always is finding the "correct" information to use.

[R H Steele]

Sometimes it's the data that doesn't match with other verified sources, this time it is their math skills 368000lbsX31.5%=115920 ( closer to 116000lbs ) --- consistency, accuracy, and math don't count for much at many of the sites...although to be fair to these folks, they do publish a disclaimer:

Quote

Note: The data found in this section is not from official railroad nor manufacturer sources. There is no guarantee provided nor implied as to the accuracy of the information here, or elsewhere on The Diesel Shop website.

31.5% for adhesion still seems too high for an SD40-2 -- all the sources I've found, or read have it pegged around 25-27% --- but I'm always willing to consider good arguments to the contrary.
Let's take the heaviest weight 400000lbs as an example, Bob's 26.5% value gives 106000lbs ste, using 35% gives 140000lbs ste.
I'm wondering two things...would a user see a difference in OR? and what would be the actual calculated ste OR would use if no traction tables were available?

[steamer_ctn]

R H Steele, on 17 December 2019 - 04:24 PM, said:

I'm wondering two things...would a user see a difference in OR? and what would be the actual calculated ste OR would use if no traction tables were available?

My quick and simple answer is:

i) It should make a difference, try doubling or tripling the MaxForce and MaxPower values to see the difference.
ii) If no traction tables are present, then OR uses the MaxForce value as the "base", and then adjusts it according to the MaxPower value at relevant speed.