[ErickC]

darwins, on 09 August 2021 - 01:18 PM, said:

http://www.elvastower.com/forums/public/style_emoticons/default/rolleyes.gif
Exactly what I want. There are some British and European locomotives with EMD and Caterpillar engines. I have little idea how they perform in terms of rpm vs Power vs Fuel Consumption - this should help me a lot.

https://web.archive....cts/fueluse.htm

engmod, on 09 August 2021 - 02:22 PM, said:

Where are your realistic values coming from?

RPM values:

http://www.rr-fallen...ual/manual.html

EMD 645E3 fuel consumption/power/RPM:

https://web.archive....ts/fuelSD40.htm

I use this curve as the basis for all turbocharged EMD engines (treat new engine rated power / 645E3 rated power as a coefficient).

EMD 567B power/RPM:

http://utahrails.net...opment_1951.pdf

I use this curve as the basis for all roots blown EMD engines (treat new engine rated power / 567B rated power as a coefficient). Caveat: remember that the curve up to 800 RPM is identical between a 567B and a 567C, the increase in governed RPM to 835 is the only source of the extra 250 HP. DO NOT USE THE DIFFERENCE IN HP BETWEEN A 567B AND 567C TO GENERATE A COEFFICIENT TO MULTIPLY YOUR POWER VALUES BY. You need to extrapolate the curve to fit the RPM range of the target engine and then do your calculations based on that. A 645E will require extrapolating this curve out to 904 RPM. Once you have calculated the power/RPM values for that curve, then, and only then, can you divide the new engine's rated power by the 567B's 1500 HP to create a coefficient to multiply the values by.

[engmod]

Hi Erick,

The question was for Elmo, but your answer is VERY thorough as usual.

[ErickC]

engmod, on 12 August 2021 - 01:22 PM, said:

Hi Erick,

The question was for Elmo, but your answer is VERY thorough as usual.

Ah, I see. I just figured there was no use in keeping the resources I've found to myself.

[Elmo313]

ErickC, on 12 August 2021 - 07:34 AM, said:

https://web.archive....cts/fueluse.htm



RPM values:

http://www.rr-fallen...ual/manual.html

EMD 645E3 fuel consumption/power/RPM:

https://web.archive....ts/fuelSD40.htm

I use this curve as the basis for all turbocharged EMD engines (treat new engine rated power / 645E3 rated power as a coefficient).

EMD 567B power/RPM:

http://utahrails.net...opment_1951.pdf

I use this curve as the basis for all roots blown EMD engines (treat new engine rated power / 567B rated power as a coefficient). Caveat: remember that the curve up to 800 RPM is identical between a 567B and a 567C, the increase in governed RPM to 835 is the only source of the extra 250 HP. DO NOT USE THE DIFFERENCE IN HP BETWEEN A 567B AND 567C TO GENERATE A COEFFICIENT TO MULTIPLY YOUR POWER VALUES BY. You need to extrapolate the curve to fit the RPM range of the target engine and then do your calculations based on that. A 645E will require extrapolating this curve out to 904 RPM. Once you have calculated the power/RPM values for that curve, then, and only then, can you divide the new engine's rated power by the 567B's 1500 HP to create a coefficient to multiply the values by.

Thanks for posting those links, Erick.

There you go Derek. No matter how stupid that post appeared, I now have more links to real world information that neither the historical society nor railway museum that I'm librarian for had in their collections. Play...tinker...ask stupid questions...make stupid posts...end result is I now have access to information I didn't have before. That's a good result.

Thanks again Erick.

[R H Steele]

ErickC, on 12 August 2021 - 04:34 PM, said:

Ah, I see. I just figured there was no use in keeping the resources I've found to myself.

http://www.elvastower.com/forums/public/style_emoticons/default/I-Agree.gif Sharing resources, is always good, nothing secret about this stuff, best to work co-operatively...that way everyone learns, helps the newcomers to OR to more easily start their learning curves...which as the simulator becomes more complex, moving towards real ops...is increasingly steep.

[Traindude]

Just thought I'd share my 2 cents on the issue. Gerry's standard .inc files are quite good, but one problem I discovered was I was struggling to get the loco started from a stop, even with a light consist. Then I looked at the .inc files and it turns out the ORTSMaxTractiveForceCurves tables' minimum speed is only around 7-10 MPH. Thus it became necessary for me to add aditional curve points for 5 MPH (2.24 m/s) and 2.5 MPH (1.12 m/s) to make starting easier. For example:

1.0 (				
			0	1219680
                        1.12    1219860
                        2.24    609840	
			5.30	257316	
			6.71	203280	
			8.94	152460	
			11.18	121968	
			15.65	87120	
			20.12	67760	
			24.59	55440	
			29.06	46911	
			33.53	40656	
			38.00	35873
                        42.47   32097	)
		)

At this time, I also revised the curves to reflect the "theoretical" tractive effort, which on most first-generation EMD units is: (308*(HP*(n/8)))/MPH, according to EMD's specification cards. In this case, n represents any given throttle notch (most USA diesels have 8-notch throttles).

To make the calculation of the theoretical TE easier, I made an OpenOffice Calc spreadsheet. By simply entering the horsepower, speed and throttle notches, a TE table is automatically generated:


Obviously, this creates some values that would exceed the "factor of adhesion" of 25% of the unit's weight, particularly in the higher notches at slow speed, but it is assumed that the parameter MaxForce would cap the max TE at the specified value, and anything higher than that would be ignored by OR.

Here are two interesting resources that can help with fine-tuning diesel performance:
Fallen Flags and Other Railroad Photos--Operator's Manual Section
Heritage Rail Alliance Resource Library

[engmod]

>throttle settings to more realistic values (eg: 0, 5%, 11%...instead of 0, 12.5, 25.

Back to the original question:-

Which model brought in the non equal notch settings as Doug alludes to above?

[R H Steele]

Traindude, on 14 August 2021 - 05:06 PM, said:

...
Here are two interesting resources that can help with fine-tuning diesel performance:
Fallen Flags and Other Railroad Photos--Operator's Manual Section
Heritage Rail Alliance Resource Library

Both Good sources, that I always refer to. I'm pleased that you made the effort to create your own curve sets. I found that creating my own curves was one of the more interesting ( and fun - actually ) learning experiences in this whole journey of learning about the physics of locomotives.

What I'm finding most particularly interesting is the difference in the methodologies we've used, which brings up a fundamental question to me.
What is an accurate description of "Tractive Force"?
Here's two sources that were helpful to me in determining what Tractive Force was. From this I also made some basic assumptions and created my curves sets...also using an Open Office calc. sheet.

Description of Tractive Force
Tractive Effort vs Power Equation

Traindude, on 14 August 2021 - 05:06 PM, said:

...Obviously, this creates some values that would exceed the "factor of adhesion" of 25% of the unit's weight, particularly in the higher notches at slow speed, but it is assumed that the parameter MaxForce would cap the max TE at the specified value, and anything higher than that would be ignored by OR.

That's interesting...never thought about it in that way. How could that assumption be tested, or perhaps someone familiar with the code would know?

I'd like to consider a couple of things, and do a little reading before I proceed further...about the differences in methodologies.

[Weter]

@Gerry
At Cruise control thread, I have shared some graphs, showing limitations for tractive force:
Those are tied with adhesion, thermal, and current limitations.
Will search for the link for you to see.
Here it is.
http://www.elvastowe...post__p__273896
Y axis is force in kN, X axis is speed in km/h one curve for one notch. "hairy" lines represent areas, where TE exceeds adhesion.
First is graph for single/double diesel engine, with 3-step automatic field weakening. Adhesion factor is 4,93
Bottom-for DC electric 8-axle engine. Dashed lines show equal traction current. Thick line at the top-max safety current threshold (600A)

[Traindude]

R H Steele, on 14 August 2021 - 10:12 PM, said:

That's interesting...never thought about it in that way. How could that assumption be tested, or perhaps someone familiar with the code would know?

I just did a test where I moved the throttle to higher notches before releasing the independent brake, and apparently I was wrong about OR ignoring higher numbers in the tractive effort curve tables. In my tests I used a A-B set of E8's and 11 of midneguy's Burlington heavyweights, and before I released the brake, the Loco and Force HUDs exceeded the 52687.5 lb (A unit) and 51875 lb (B unit) limits I entered for the MaxForce parameters, but I didn't encounter any wheelslip until I released the brake with the throttle at notch 4 or higher.

Then again, such scenarios where it is necessary to start from a stop at notches higher than notch 2 are rare IMO, so I'll probably leave my modified curves as-is for the time being.

[Weter]

And in case of starting from uphill?

[steamer_ctn]

R H Steele, on 14 August 2021 - 10:12 PM, said:

That's interesting...never thought about it in that way. How could that assumption be tested, or perhaps someone familiar with the code would know?

My understanding is that in the real world starting TE (MaxForce) is not capped as such, it could reach a much higher value. The MaxForce value is the typical "design" value when wheel slip may start to occur, and hence in practical terms the locomotive cannot produce a greater value of starting tractive force (otherwise wheels start slipping, and the locomotive won't move).

OR caps the MaxForce to the value set by the user, however the performance of the locomotive is also dependent upon the adhesion of the locomotive. Hence if the MaxForce exceeds the Adhesive force (related to adhesion) then the locomotive will not be able to exert its full starting TE.

[R H Steele]

Traindude, on 14 August 2021 - 05:06 PM, said:

Then I looked at the .inc files and it turns out the ORTSMaxTractiveForceCurves tables' minimum speed is only around 7-10 MPH. Thus it became necessary for me to add additional curve points for 5 MPH (2.24 m/s) and 2.5 MPH (1.12 m/s) to make starting easier.

The minimum speed for the ORTSMaxTractiveForceCurves I've constructed is set when Notch8 attains maximum Tractive Effort. Other power settings lower than 100% will also attain this MaxTE, however, it will be at a lower speed. The lowest speed of each notch is zero m/s, Hopefully the OR interpolator will generate the correct tractive effort for each notch for speeds that fall below the minimum speed down to zero.

Two possible problems: Does the OR interpolator work properly in this instance? (I'm assuming – yes ) ...and...That I've capped the maximum for each notch...I'm not entirely positive that presents no problems. Especially since steamer_ctn in post#22 provides this information:

steamer_ctn, on 15 August 2021 - 04:24 PM, said:

My understanding is that in the real world starting TE (MaxForce) is not capped as such, it could reach a much higher value. The MaxForce value is the typical "design" value when wheel slip may start to occur, and hence in practical terms the locomotive cannot produce a greater value of starting tractive force (otherwise wheels start slipping, and the locomotive won't move).

OR caps the MaxForce to the value set by the user, however the performance of the locomotive is also dependent upon the adhesion of the locomotive. Hence if the MaxForce exceeds the Adhesive force (related to adhesion) then the locomotive will not be able to exert its full starting TE.

I'm working on refining the curves and this is something I'm going to work on. Additional speed points below the minimum already given in the curves may be necessary ( especially if the OR interpolator does not apply to this case )...knowing more about the interaction between MaxForce and Adhesive Force will be helpful. Sources –- anyone?

Traindude, on 14 August 2021 - 05:06 PM, said:

To make the calculation of the theoretical TE easier, I made an OpenOffice Calc spreadsheet. By simply entering the horsepower, speed and throttle notches, a TE table is automatically generated...

I'm assuming the spreadsheet example was for an EMD E8? If so, that brings up another question I have. The E8 is listed as 2250hp –- power delivered to traction motors. My understanding is that rail horsepower is used to calculate tractive effort.

One item that would help me is to have an example of the “light consist” that gave you problems starting --- locomotive/s, number of cars, and total car mass, grade...that would help me test. The starting problems could be from other factors that neither you or I have thought of. I would like to try and duplicate your experience so I could refine my testing.

[pschlik]

For reference, most freight locomotives can dramatically exceed their adhesion rating. I don't know how locomotive companies ever figured out exactly how much tractive effort is possible where adhesion is not a problem (since it basically always is a problem), but they know stuff like a GP39-2 could theoretically pull off 87,000 pounds of tractive effort despite the fact that you'd never get more than about 55,000 pounds out. This 87,000 pounds is the max you could get out of any 4 axle locomotive with the D77 motors (GP15, GP38, GP40, etc) as that is what occurs at the 1,500 amp limit of the motors.

https://i.imgur.com/BuoLkFk.png


The habit many OpenRails creators have of limiting the tractive effort curves to not exceed the adhesion rating of a locomotive is outright wrong and I abandoned that practice in my physics set months ago. I'm pretty sure this practice came about as a crude way to reduce wheel slip (since, ya know, wheel slip protection isn't simulated and every time it's proposed there are just excuses and workarounds proposed instead of actually solving the problem), which is fair enough, but we shouldn't go telling ourselves this is realistic.

[engmod]

steamer_ctn, on 15 August 2021 - 04:24 PM, said:

My understanding is that in the real world starting TE (MaxForce) is not capped as such, it could reach a much higher value. The MaxForce value is the typical "design" value when wheel slip may start to occur, and hence in practical terms the locomotive cannot produce a greater value of starting tractive force (otherwise wheels start slipping, and the locomotive won't move).

This is true for the first generation diesels as they had no control of current.

The second generation with electronic controls ( sd40-2 and later ) did limit the starting current. I don't know when GE started electronic control.