Re: Steam Physics

DarwinS · Post by **DarwinS** » Wed Mar 01, 2017 5:54 pm

Thanks will correct things before further use... all these numbers must be confusing me.

copperpen · Post by **copperpen** » Wed Mar 01, 2017 8:38 pm

@Darwin

I now have the Stranraer route installed. Just tried a run out of Girvan. That is one long steep climb.

systema · Post by **systema** » Thu Mar 02, 2017 8:41 pm

I just get more and more confused.

I have set up the BR Standard 8P with 32 ton carriages. The performance and efficiency tests show 71000 doing 80mph with a load of 586 tons. I tried a run with a load of only 448 tons and can barely reach 75mph. This was with the standard calculated Davis figures set favourably for the C value and all basic steam parameters of the loco correct. I would have to make a large reduction in train resistance to get 80mph with a 586t load.

OR HUD shows a maximum IHP of 2188. I have worked out that in OR this depends on Boiler Pressure, Cylinder Diameter and Cylinder Efficiency. Yet the test report shows a photograph with IHP at 2400. What's worse is I translated the locomotive resistance curve from the report onto the Fcalc graphs which gave far higher resistance than basic Fcalc.

As an aside the 32t UK carriage curve from the report shows a close correlation in the area of 75-90mph to basic Davis results. So using 'real' data makes no odds to likely top speed with carriages.

I really don't understand what's going on.

Mick Clarke
MEP

copperpen · Post by **copperpen** » Fri Mar 03, 2017 3:49 pm

First of all, when I set up my carriages I used the MK1 and a set of Davis figures from Fcalc. I then made a consist with one MK1 and the US Atlantic which was already set up for high speed running. I ran that consist and noted the resistance figure for the carriage at every 10 mph mark. Comparing those figures with the plotted curve showed that resistance was too high, so I lowered the C value and tested again. Kept at it until my curve was a very close match to the published one.

Turning to the 71000, I have taken the frontal area from the eng file figures, used Fcalc to produce my Davis figures using 180kmh for the speed and the other figures were taken from the Haresnape book on Ivatt and Riddles locomotives.

My test train is 19 mk1 ( 598 tons ) plus engine and tender, not added Davis figures to the tender yet, but I have reached almost 70mph on the first run using a minimum spec OR eng file.

After a few runs gradually reducing the locomotive Davis C value, I worked up an OR advanced eng file and went for another run. Halfway round the CTN test track level oval, I reached 78.1mph using 35% forward and 85% throttle, but got a warning about overworking the fireman.

I then retuned the eng file with a lower boiler output which put a limit on the amount I could use and tried another run. At the same point as the previous run I recorded 75.3 mph. That to me is well within the "ballpark".

My carriages use ORTSDavis_A ( 482.68 ), ORTSDavis_B ( 11.1877 ), ORTSDavis_C ( 0.4952 ), ORTSBearingType ( Roller )

Locomotive is ORTSDavis_A ( 7458.55 ), ORTSDavis_B ( 30.9307 ), ORTSDavis_C ( 1.8 ), ORTSBearingType ( Roller )
Tender at present is using the same as the carriages.

Adding ORTSCylinderEfficiencyRate ( 1.097 ) to the eng file will give you a MaxInd of 2400 in the HUD.

If you consult the manual you will find some parameters that can be used to produce figures a little bit different to the plain jane set generated by the OR code.

systema · Post by **systema** » Sat Mar 04, 2017 10:37 pm

I can easily get to 80mph with the 8P and 608 ton load with Copperpen's Davis figures and the Cylinder efficiency of 1.097. But I have a problem with this. Firstly there can be no such thing as an efficiency of greater than 1.0 (100%). When this is entered into the eng file the Theoretical Tractive Effort increases to 41Klbf from 39Klbf. So this is not using real world figures. The max IHP of 2400 stated in the real world figures is not reachable in OR with correct parameters entered unless the efficiency is increased beyond 100%.

My next problem is with the Davis figures. Here are the resistance curves for a 32 UK ton Carriage with Davis from Fcalc, the Plotted Graph from the real world, the fixed curve to meet the plotted graph all taken from the ideas proposed on CTN, plus Copperpens figures.

Copperpens figures seem to me to be clearly very low compared to the so called real figures.

Here is the Locomotive graph showing a similar situation with Copperpens resistance numbers

Again I don't think Copperpens Davis numbers are close enough to the real world but they do give a performance that reflects that stated from real world results. That's why I am confused. There is surely something wrong somewhere.

Mick Clarke
MEP

copperpen · Post by **copperpen** » Mon Mar 06, 2017 9:50 am

I tend to agree with your general line of reasoning. Accepting that using correct data for dimensions and weight gives correct output in terms of steam generation and starting TE, and subsequently while in motion, the power output is correct, leaves us with two problems to solve. First, why is the IHP so divergent from the MaxInd when working hard and second, why does the code not give correct results for normal Davis figures.

I did get a matching curve while testing, but then found like you have that the train performance fell short of recorded statistics. That is why I have "massaged" the C figure to allow performance to match the real world. Without doing that, it is impossible to arrive at stations on time, and drives fuel/water usage up too high as well. Everything was fine until we started to use Davis figures.

Cylinder efficiency allows a user to modify performance. With the figure of 1.097 I can get the max of 39K TE that the 71000 was capable of, but not the theoretical 41K.

There is another modifier that can be used as well, ORTSBoilerEvaporationRate which defines how much steam a boiler will produce, using that I have limited the 71000 to just over 37K lb/hr maximum. That figure restricts just how fast one can drive the locomotive without using more steam than is produced

systema · Post by **systema** » Mon Mar 06, 2017 10:56 am

Cylinder efficiency allows a user to modify performance. With the figure of 1.097 I can get the max of 39K TE that the 71000 was capable of, but not the theoretical 41K.

I noticed that if I increased the cylinder eff from 1.0 to 1.097 as you suggested this did give me max IHP of 2400 but it also increased the Theoretical TE shown in the HUD above 39K to 41K which is incorrect for the given real parameters.

Looking at my curves and further reading of 5AT I think the locomotive resistance curve actually includes the tender. If so. that explains why the plotted curve is so far out to fcalc. However, using fcalc resistance does not allow adequate performance. It can only be achieved by massaging the resistance and max IHP.

I also checked the resistance figures shown in the HUD at various speeds and they correlated exactly with the calculated output for the eng/wag file coefficients A, B and C at each speed.

Peter has asked me to send him my files for 71000 and carriages so he can check it out.

Mick Clarke
MEP

DarwinS · Post by **DarwinS** » Mon Mar 06, 2017 2:09 pm

I can confirm that the published curves consider locomotive and tender together.

systema · Post by **systema** » Mon Mar 06, 2017 10:39 pm

Further testing with 71000 plus 608 ton load. Target speed 80mph

I have concluded that using Davis Calculations does not give proper results. Wardale on the 5AT website demonstrates two formulae based on actual tests.

Locomotive rolling resistance: R ≈ (45 + 0.24v + 0.0036v2) N/Tonne

Carriage rolling resistance: R = (1.1 + 0.021v + 0.000175v2) kg/tonne - from Koffman applying to BR coaches.

I have adapted these for OR and got reasonable results. Wardale notes that there is probably an error with the carriage B coefficient of 0.021, but strangely continues to use this figure in working out carriage resistance for a BR coach.

The Locomotive Resistance is derived from averaging real results from the non streamlined Rebuilt Merchant Navy Class and the BR Standard 8P, both of which have similar dimensions and weights. There are various conversions that have to made to get to numbers that OR understands (Newtons and Meters per second). You will note that the two resistances are quoted in different units per tonne just for starters. I have assumed that the locomotive resistance includes the tender. This is based on the way the numbers are used by Wardale to calculate other things such as maximum loads on gradients. In order that OR can read the resistance properly the locomotive resistance needs to be split into Re for the engine and Rt for the tender. At this stage I have assumed for simplicity a loco of 100 tonnes and tender of 50 tonnes. This is roughly in line with the MN and 8P weights. Without going into detail I came up with

Re = 3960+49.28v+3.55v^2
Rt = 540+37.00v+0.72v^2

Rt is derived from the Koffman formula above, but converted for a tender weight of 50 tonnes.

Assuming the BR carriage is 32 UK tons

Rc = 351+24v+0.72v^2 (Note that the tender C value has to be the same as the Carriage C value if of similar dimensions)

Using the above figures in OR my train could only reach 78mph. The real world tests show it should be capable of 80mph. If however the tender and carriage coefficients are modified in line with the B value derived from the plotted curve from the real world this would give B= 27.7 for the tender and B=18 for the carriage. Remember, Wardale indicates the Koffman figure is wrong.

Amazingly substituting the revised B values now gives me the 80mph target speed, with 25% cut off and IHP of 2257. NOTE: the loco cylinder efficiency has to be set at 1.097 to achieve this. This is theoretically impossible as you can't reach better than 100% efficiency. Changing the CE also increases the Max Theoretical TE to 42Klbf from 39Klbf. If the CE is set at 1.0 I can only achieve 76mph.

CONCLUSION. Serious consideration needs to be given for deriving a set of Resistance formulae for various OR steam stock items based on the Wardale results. These could be placed in an excel spreadsheet which would calculate OR resistance coefficients for various stock items and weights. The problem of the Max achievable IHP also needs to be solved. Peter Newall will be looking into this in the near future.

I will continue looking into resistance and try to come up with figures for freight and other types of Steam Loco.

Mick Clarke
MEP

DarwinS · Post by **DarwinS** » Tue Mar 07, 2017 7:52 am

CONCLUSION. Serious consideration needs to be given for deriving a set of Resistance formulae for various OR steam stock items based on the Wardale results. These could be placed in an excel spreadsheet which would calculate OR resistance coefficients for various stock items and weights.

This is definitely top priority!

However with regards to the ORTSCylinderEfficiencyRate ( 1.097 ) in order to achieve the IHP recorded for the prototype I think we need to check with Peter what exactly this means. I would agree that greater than 100% efficiency is not a realistic parameter, but on the other hand if ( 1.0 ) is an index value that refers to the efficiency of a particular locomotive used to develop the model then it is possible that other locomotives could be more efficient as well as less efficient.

With this in mind Systema notes that to get an IHP of 2440 then theoretical tractive effort needs to rise above 39 klbf. In the normal way this figure is calculated based on 85% of boiler pressure being available... if we could make 100% of boiler pressure available then a maximum of 46 klbf could be produced. This may seem unlikely but look at the curves for ITE in the test report. http://users.fini.net/~bersano/english- ... R_Std8.pdf

From graph 13 in the report the output of 2440 ihp at 80 mph with 20% cut off would correspond to a steaming rate of about 33 000 lb/hr and a combustion rate of about 6 000 lb/hr. If you match this to the tractive effort curves in graph 12 then this corresponds to an actual tractive effort of 12 klbf at 80 mph or 36 klbf at 20 mph and would most probably correspond to a starting tractive effort of greater than the theoretical 39klbf. (If in reality the locomotive could ever produce an equivalent or greater TE effort starting from rest is a different question again!) I did try putting some data for this locomotive into an eng file and noticed it does have a tendency to slip...

copperpen · Post by **copperpen** » Tue Mar 07, 2017 8:02 pm

I have been doing some more test running with the 7100 today as well, specifically looking at IHP. I have made my test consist of all MK1s at 40tons each representing a fully loaded 15 car train, exactly 600 tons.

I went back to Fcalc to regenerate some proper figures, where I found something most unusual. There are two options, metric or US measurements. The US measurements give very much smaller figures than metric for the Davis formula, so I went with the metric set. 4330.86, 33.8494 and 6.267609. This gave a lower curve that the 8P test shows so Fcalc looks to be not very accurate for use in OR, but I was able to almost reach 70mph

Back to the IHP figures while running. In the 8P test papers there are a set of indicator diagrams with steam rate and IHP for several different states of running. Taking 60mph, full regulator and 7% cut off, the diagram shows 1397HP and 18900 lb/hr steam. Open Rails under the same conditions gives 970HP and 15351 lb/hr of steam.

This is why OR cannot handle proper Davis figures. I have informed Peter of my findings.

With regard to the cylinder efficiency rate the original intention was to have some way to model engines that were poor steamers and those that were very good along with the more usual normal good ones. That has been overtaken to some degree with the addition of valve events, but that does require some good data to convert into OR pairs. It was never the intention to use it to increase the theoretical TE figure.

systema · Post by **systema** » Tue Mar 07, 2017 9:56 pm

This may be of interest. I don't know if anyone on the OR team has seen this. Download the pdf by clicking on the thumbnail.

http://railknowledgebank.com/Presto/con ... RfMTc2MzM=

Very interesting modern day take on Davis. In a nutshell it concludes that Davis numbers are too conservative. Another conclusion is that the B coefficient is not relevant. You may have noticed many formulae on 5AT do not have the speed dependent coefficient included. Also the longer the train beyond about 10 wagons the less the overall air friction per wagon, as it tends towards a constant after about 10 wagons. I am still trying to take it all in.

Regarding Cylinder efficiency it is obviously a good idea to have a means of reducing the output but it should not be possible to increase it beyond the maximum value. Perhaps the code could be changed to only allow CE to equal 1.0 or less.

Very interesting find regarding steam rate produced in OR as against the real figures. I think with a combination of better resistance numbers and improved steam performance we will be there. That would leave the Vacuum Brakes as the main bugbear. We need to able to stop from speed in about 1000 yards with a longish train!

Mick Clarke
MEP

systema · Post by **systema** » Tue Mar 07, 2017 10:06 pm

I went back to Fcalc to regenerate some proper figures, where I found something most unusual. There are two options, metric or US measurements. The US measurements give very much smaller figures than metric for the Davis formula, so I went with the metric set. 4330.86, 33.8494 and 6.267609. This gave a lower curve that the 8P test shows so Fcalc looks to be not very accurate for use in OR, but I was able to almost reach 70mph

The US figures are in US tons, pounds, feet and mph. Remember a US ton is only 2000lbs. If you convert the US output to Newtons and Meters per second you get the same result as if you had inputed the correct metric figures on the metric option. OR understands the metric Davis numbers without needing any units being specified so you did the right thing.

Mick Clarke
MEP

steamer1960 · Post by **steamer1960** » Wed Mar 08, 2017 5:28 am

I am ready to start having a look at the performance of the 71000.

Before I start, I would like to confirm my understanding of the performance criteria expected.

Based upon my understanding of the thread, it appears that 71000 is expected to pull a load of 586 tons and reach a speed of 80mph.

How was this determined?

I am assuming that it is based upon Controlled Road Test No 10R (graph 55). This test does show that 71000 reaches a speed of approximately 80mph near Steventon, but this is on a long downhill grade. In other places where the train faces uphill grades the speed appears to be only approximately 60mph. So it would be good to eliminate as many variables as possible created by changing gradients.

Graph 54 appears to show the characteristics produced by test No 10R, and it shows that with a trailing load of 586 tons, the expected maximum speed on a level track will be approx 73mph (where curves C, D, and E cross).

I therefore propose a performance test for 71000 as follows:

Trailing load: 586 tons (18 x 32 ton cars) - running with 19 cars increases the trailing load by 3% (or adjust weight of each car to get the actual value)
Test track section: Level, CTN track has a long level section of track
Test Aim: For locomotive to reach a maximum speed of approximately 73mph on a level track

Is this an expectation that we can agree upon?

systema · Post by **systema** » Wed Mar 08, 2017 2:15 pm

Peter,

My information was taken from the photograph of the test train where it is shown passing Didcot. This is a little further on than Steventon but also on the end of a long steady downhill run of approx 0.13% gradient. I have done a rough calculation allowing for the reduced resistance due to the gradient and its about 2200lbf less. Finding an approximate point on the curve for reduced resistance crossing C& D curves is about 80mph.

Your estimate of max of 73mph on level track looks about right.

I have been looking at info on the one off 71000 and apparently it was not all that great under BR so we may have been expecting too much from it. For example it did not have very good drafting qualities. Since preservation it has been much improved.

Judging from my previous runs I think it will reach the target even with default Fcalc resistance and default OR parameters.

Copperpen has described problems meeting timetables with the default OR and Fcalc settings so is the acceleration an issue?

Mick Clarke
MEP