Adhesion

Is there formula for calculating adhesion with MSTS? We are looking for a formula to using weight and tractive force horsepower the fits the requirements setup within the MSTS program putting in the real world values does seem to work in the MSTS world. We need to find a formula that fits MSTS. Or some insight into how MSTS derives there Adhesion calulations.
Thanks for any input you might be able to give us.
Teacherpat

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RE: Adhesion, plainsman, Sep-22-03, 12:29 PM, (1) RE: Adhesion, ctillier, Sep-22-03, 01:26 PM, (2) RE: Adhesion, plainsman, Sep-22-03, 01:32 PM, (3) RE: Adhesion, Teacherpat, Sep-22-03, 05:30 PM, (6) RE: Adhesion, plainsman, Sep-22-03, 10:20 PM, (8) RE: Adhesion, plainsman, Sep-22-03, 10:34 PM, (10) RE: Adhesion, plainsman, Sep-22-03, 10:35 PM, (11) RE: Adhesion, jtr1962, Sep-22-03, 03:14 PM, (4) RE: Adhesion, plainsman, Sep-22-03, 03:39 PM, (5) RE: Adhesion, jtr1962, Sep-22-03, 05:45 PM, (7) RE: Adhesion, xlspecial261, Sep-22-03, 10:31 PM, (9) RE: Adhesion, plainsman, Sep-22-03, 10:41 PM, (12) RE: Adhesion, xlspecial261, Sep-22-03, 11:24 PM, (13) RE: Adhesion, plainsman, Sep-22-03, 11:41 PM, (14) RE: Adhesion, xlspecial261, Sep-22-03, 11:55 PM, (15) RE: Adhesion, jtr1962, Sep-24-03, 11:27 PM, (16) RE: Adhesion, CPR_Malice_96th, Sep-25-03, 09:52 AM, (17)

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I suggest you download V4.5 physics files and examine how the adhesion and other properties relate to one another and real world data. Several factors like numwheels are important to integrate with the adhesion data to make the sim perform more realistically.
For example, here is data from a U23B, a typical diesel electric from the US.
Adheasion ( 0.24 0.49 1.8 0 )
MaxPower ( 1680kN )
comment( 2,250 HP )
MaxForce ( 296.0kN )
MaxContinuousForce ( 274.45kN )
MaxVelocity ( 70mph )
MaxCurrent ( 1500A )
WheelRadius ( 20in )
Sanding ( 15mph )
NumWheels ( 4 )
Hope this helps,
Bob BoudoinBTW, if you have a particular locomotive you are trying to match, I would be happy to help you with the specific data parameters, if you have specs from the real world.

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Hi BobMaybe it's a typo, but MaxPower should be in kW not kN.cheers

--
Clem

http://www.tillier.net/speedworks/index.html

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Hi Clem,
Thanks for catching the typo,
2,250 HP is 1677.8 kW or kilowatt not kN as noted above.
Thanks again,
Bob

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Thanks you have provided us with lots of information to use in our work with setting up our train simulations. We are trying to find the logic behind the numbers associated with the various calculated forces influencing the locomotives within the simulation.

Maybe you can help us with this one and we can examine it and apply it to other engines. Thanks for any help you can give us.Looking at the steam engine BigBoy- 6250HP (4690.453 kW )
Tractive Effort 135,350lbs. (602.06387 kN )
WT. 500 Metric Tons
68 Driving Wheels
8 Axels
Wheel Radius 0.8636m
What would be the Adheasion?One other question, what is the criteria used to determine the number of numwheels for first part of the engine file and then what is the criteria for determining the number in the second part of the engine file? So for example what would the number of numwheels be for the engine above in the 1st wagon section of the engine file? What would the number of numwheels be for the engine above in the 2nd section of the engine file? We appreciate your taking the time to increase our understanding and make this a more realistic simulation.
Thanks again.
Teacherpat

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Hi Teacherpat,
I think you probably picked the worst possible example to apply the rules upon?? The Big Boy presents several problems that are partly just beyond the original design concept of MSTS in its current version. The model is actually two locomotives. Now if you put all the "go" into the lead locomotive, you will need to account for 1,208,750 pounds of locomotive. Unfortunately, the sim designers did not anticipate this much weight, and the sim starts doing some strange things if that much weight is used. Now if you break the file into two parts, the problem becomes that the sim does not model a trailing locomotive in quite the same way it models the lead. This seems to be particularly problematic in doubleheaded steam. The result is the trailing unit does not perform as well as the lead, therefore for a Big Boy, the combination is not as good as the whole locomotive. I am not saying a good .eng file can't be written for the locomotive, but every attempt I have seen fails to perform properly in some part of the performance envelope?

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part 2:
About the largest and most potent steam locomotive i have been able to model to somewhat prototypical performance, is the Texas & Pacific 2-10-4 "Texas" type. I have a series 3 (there were 4 series of these locomotives, each with slightly different performance) version which seems to model the prototype quite well. I run it in a reskinned Selkirk (not a perfect visual model, but it works for me), and can run an impressive freight on the FBL.
Another thing to keep in mind, the Big Boy was not as powerful as many expect. It was designed to move a 3,600 US ton train at 45 mph up a 1.14% grade. It will barely start a 6,500 US ton train on a FLAT grade. It is really in its element after the locomotive reaches 40 mph, but is much less potent on starting a train, as the power curve drops off a lot at slow speeds.

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part 3:
Now as to adhesion, steam locomotives have inherently poorer adhesion than even the worst diesel electric. The reason, is that the power stroke is not a smooth application of torque, but rather is quite variable, depending on what part of the cycle the wheel is in. Also keep in mind that all the wheels change torque at the same time. This results in a much lower adhesion ability. A steam locomotive that gets 17% adhesion is probably among the best of its type. Most would probably be closer to 15%.
Hope this helps,
Bob

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There are four numbers in the Adheasion parameter(note the odd spelling). They work as follows(the fourth value doesn't appear to be used at all):Tractive Effort(slipping) = (first value)*(third value)*(locomotive weight)/(NumWheels) Tractive Effort(normal) = (second value)*(third value)*(locomotive weight)/(NumWheels) Tractive Effort(sanding) = 0.95*(third value)*(locomotive weight)/(NumWheels) I also discovered that these same values are used while braking, but for the locomotives only. The first occurence of NumWheels(in the wagon part of the .eng file) controls adheasion while braking and the second occurence(in the engine part) controls adhesion while under power. NumWheels and Adheasion have no effect whatsoever on the braking of wagons. The only ways to control the braking of wagons are to adjust the MaxBrakeForce and BrakeCylinderPressureForMaxBrakeBrakeForce parameters. The sim uses multipliers to account for reduced adhesion under rain and snow conditions(the values are 0.9 and 0.55, respectively, and can be adjusted in the default.wag file). These multipliers affect the tractive effort(and braking for locomotives) under slipping and normals conditions only. The tractive effort while sanding remains the same even in bad weather, and interestingly, you can also increase the maximum brake force exerted by the locomotive by sanding while braking. Once again, there is no change whatsoever in the braking behavior of wagons under bad weather conditions. This is dependent only upon the MaxBrakeForce and BrakeCylinderPressureForMaxBrakeBrakeForce parameters, and remains the same in all types of weather.

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Hi Joe,
I know we have discussed this before, but for new folks that missed the previous discussion, I think the disparity between the rain and snow adhesion is far too great. The intense pressure under the wheels of a locomotive will greatly reduce the differential due to these two states. I would suggest more like 0.8 and 0.68.
Also, note that in the above example I am using 1.8 for the third factor, an adjustment for transmission efficiency, instead of the 2.0 default value used in the sim.
Bob

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>I know we have discussed this before, but for new folks that
>missed the previous discussion, I think the disparity
>between the rain and snow adhesion is far too great. The
>intense pressure under the wheels of a locomotive will
>greatly reduce the differential due to these two states. I
>would suggest more like 0.8 and 0.68. Agreed. The enormous contact pressure basically means you're driving on watery slush, not ice, except possibly at very cold temperatures(maybe in the -40°F range). Anybody know more about this?

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Neither rain nor snow have a huge effect on adheasion in the real world. Some effect, yes. But not a huge one.I would use .95 for both.Snow can play havoc with your braking however. Not the dynos, but the train and independant brakes due to snow buildup on the shoes. When I was working in the yard, I would leave ten pounds on the independant at all times to keep them cleaned off and warm. Worked like a charm. And sure beat going through a switch with a light engine because it wouldn't stop. Todd

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LAST EDITED ON Sep-22-03 AT 10:48 PM (EDT)

Hi Todd,
I would expect this with modern AC types, but will this same rule apply to older DC types, particularly before anti-slip computers, 0.95? Also, I have seen many accounts of a Dash 9 dropping from 28-30% adhesion in dry to 22-23% in wet. This is where i get the 0.80 for rain.
Bob

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LAST EDITED ON Sep-22-03 AT 11:25 PM (EDT)

With the older DC power you have to go by the seat of your pants due to the fact there is no computer to tell you what the chooch is doing. Hence, I can't quote exact numbers.My own experience is with SD40-2's and SD60's. Since we don't have any Dash 9's, I can't really compare other than to say that a 4400 HP Dash 9 will have 733 HP per axle while a SD40-2 will only have 500. The SD likely has enough margin that rain doesn't make a big difference (with the sand on anyway). As mentioned in a previous post, I've had AC4400's slip so bad at 40MPH, in the rain, they derated down to 1500HP before recovering. Why? I dunno. Guess those computers aren't all they are cracked up to be.
I can only relate a couple experiences off the top of my head that might help you come up with some adhesion numbers.One is a loaded coal train with two SD60's and a SD40-2 (ex-MILW even. ) 16,500 ton train up a .66% grade with a long 1 degree 57 minute curve on the head end witht he tail in a short 2 degree. Speed was a steady 14MPH in the rain.The other I don't really have enough info as I don't know the grade exactly. When working the hump job at Bensenville, I pulled a 9000 ton track out of the arrival yard, which is bowled somewhat on the west end(the end I was pulling). With sand and holding the independant on slightly to control wheelslip, the single SD40-2 pulled the track right out.One thing I should mention, and you already know Bob, is that while a SD40-2 way be nominally rated at 18% adhesion, that is an all conditions number. I know I've gotten a lot more than that out of one before. It's just that short of having the dynamometer car in tow, it's hard to put a number on what they are really putting out.Basically what I'm saying is, I've never been worried about it raining or snowing when I head out of town. Granted, I don't run in the mountains. BUT, we do have hills around here and trains are powered accordingly. We don't go up Rio Hill, .7%, much faster than the mountain boys do out in the Rockies. so we would notice a big drop off, and I really dont.Hope this helps. I know it's kinda disjointed, but if there is a specific question you have out of this mess, let me know. Todd

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Hi Todd,
These numbers only modify the performance without sand, I think that is where we may be on different numbers. The sim uses the same adhesion under sanding for all conditions.
Bob

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Hmmm. Well, generally I don't need to use sand much above 10 MPH. Above 20-25 it doesn't do a whole lot anyway as most of it blows away before going under the wheels and your TE isn't so high then.On top of it, when taking a hard pull from a stop, I just automatically turn on the sand out of habit. Kinda hard to get good numbers from me. Seriously though, I don't notice much difference, rain or dry. Certainly not a 20% drop. I'd say 10 percent max, while putting a 5% drop in my own stuff.It should be noted that in the case of the coal train I mentioned, only lead axle sand was used. Not trainline. Sand yes, but the second and third units weren't seeing much of it. btw-Drop me a mail. I tried sending you one concerning the autorack physics a couple weeks ago and it bounced.milw104c@charter.netTodd

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This has some info on adhesion versus speed among other things: http://www.irieen.com/questrs.htmVery interesting reading.

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This is one area of the sim that I really understood better.I guess no time like the present to start learningK maybe tommorrowTim Kent
96th_Malice
" Power for You "

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