The right trucks - and the right bearings, for the archives - wrap-up


devansprr
 

--- In STMFC@yahoogroups.com, "Aley, Jeff A" <Jeff.A.Aley@...> wrote:

Tim,

Thanks for letting me know your opinion.

So far, I judge this thread to be acceptable.

Regards,

-Jeff Aley
Moderator, STMFC

All,

Begging the moderator's indulgence one last time, I wanted to wrap up my part of this thread to include some Internet research I conducted over the past few evenings. I am also sympathetic to Tim O'connor's concern that this was wandered off topic.

Therefore this post has been divided into four topics:

1) STMFC modeling that may need to reflect bearing types (journal vs. roller). Clearly STMFC content.

2) The impact of roller bearings on STMFC era operations – marginally on topic

3) Relating model railroad wheel set selection to journal vs. roller bearings (slight tongue in cheek)

4) The prototype engineering behind all this, including an update to modern investigations into freight train resistance.

The sections are ordered to reflect what I suspect is a decreasing level of interest among some on this list:

1) STMFC features that distinguished roller bearings (RB) In a manner that might be reflected n STFMC models:

1a) The first large scale RB installation to freight cars (besides testing), was a refit of 300 UP stock cars in 1947, followed by 1000 new C&O hoppers. The UP cars, as retrofits, featured journal box covers that are difficult to distinguish from plain journal bearings. But the C&O hoppers (79000 series) clearly have journal covers that look very similar to passenger car RB covers of the day – they do not resemble plain bearing journal boxes with flip up lids for maintaining journal bearing oil levels and packing/wiping materials.

1b) The C&O cars included a fat white strip under part of Chesapeake and Ohio to indicate they were roller bearing equipped. Steve Lucas has a 1958 ETT that makes note of this mark, and instructs crews in special handling of RB equipped cars, since the slippery little devils will roll a lot more at low speeds than plain journal bearing equipped cars. It would be useful to know if other ETT's of the late STMFC era had similar notations, and if that might mean specific marks need to be included on 1950's STMFC models from railroads other than the C&O.

1c) RB installations began in earnest in the early 1950's, and the ASME book indicates that freight cars were being equipped with roller bearings at a rate of just under 1% of the national fleet per year throughout the mid-to-late 50's. All of this was long before RB's were mandated, so it appears that RR's were installing RB's on freight cars used in captive service. If most RB installs were on new cars, and they were generally used in captive service, and if about 2.5% of the nation's freight car fleet was replaced every year, then as much as 30 to 40% of new car construction in the mid to late 50's would have been RB equipped. So this is a distinctive feature that 1950's era modelers may need to research.

1d) For the STMFC era, it appears that RB installs were limited to cars in captive service. Candidates include merchandise express cars, stock cars, hoppers, and I am not sure what else, although I suspect many on the list will be able to provide insight into this topic. Conversely I suspect that private owner cars (such as tank cars) would not be RB equipped (why "waste" their money on more expensive bearings – it wouldn't save them any money). Perhaps some of the RR owned reefer companies would install RB's. I would think that general service XM's would not. RB installation on new and rebuilt cars was not mandated until after the STMFC era.

1e) Coming full circle to the original topic of this thread, it would seem that for those modeling late in the STMFC period, accurate model trucks will need to reflect the proper type of bearing – plain journal bearing, or roller bearing.

2) Impact of bearings on STMFC operations.

2a)The limited deployment of RB's in the STMFC era had little impact on freight train performance, although it did impact some individual car handling tasks, such as the C&O ETT instruction to not hump RB equipped cars and apply special practices for spotting RB equipped cars. It would be interesting to know if other ETT's and/or rulebooks had similar rules/guidance.

2b) The important operations lesson from this investigation is the MUCH higher plain bearing friction at very low speeds, and especially when stopped. With plain bearing starting friction being as much as 10 times the rolling friction at 10 mph, the starting friction helps explain the need to "take slack" before starting a long train during the steam era, and the need to quickly get cars moving, and keep them moving, at speeds of several miles per hour. I could not find an authoritative source describing a critical "minimum" speed, below which a long train on level or uphill grades was likely to stall. Based on the data I have reviewed, my "best guess" is that the minimum speed would be around 3 mph. This could explain why STMFC era trains, especially those powered by steam, were "walked out" when starting at a walking pace – not a crawling pace. Perhaps videos can confirm this, but personally I will no longer be concerned about trying to have model steam locomotives pull long freight trains at 1 smph – simply not prototypical.

2c) But in the end, once above 10 mph, the difference in rolling resistance between plain journal bearings and roller bearings is equivalent to only a 0.1% grade, which also means RB's did not lead to much higher train tonnages, because at speed the other sources of resistance are much greater. But considering that a journal bearing's starting friction was equivalent to a 1.75% grade, it is possible that tonnage ratings for ruling grades could be increased for steam powered trains since it would be easier to restart on a grade if RB equipped, and then work up the grade at lower speeds without stalling. (Note that when starting a plain bearing train, by taking slack, only a few cars are in the very high friction regime at any given instant – the rest of the train either hasn't started moving yet (still slack between it and the locomotive,) or the moving part of the train is already up around 3 mph, where friction is likely 1/4 or less of the starting friction).

2c) Engineering data would suggest that plain bearing equipped cars stopped on a 1.5% grade would likely stay put, even without brake application. So no worries for spotting plain bearing equipped cars on slight grades. RB equipped cars could start rolling on grades as gentle as 0.05-0.1%.

3) Unfortunately for Doug Harding and Bill Schneider, there is no way to simulate plain bearing friction on a model railroad - good wheel sets are a good approximation of plain bearings above 3 to 4 smph, and lousy wheel sets are only accurate when stopped, or just starting (But with so much drag above 3 smph there is the issue of whether or not the train could climb a helix – as discussed before). Conversely, really good wheel sets may approach prototype RB equipped car resistance – although RB's contribute a very small portion of modern freight car resistance. (See the next section).

4) For those willing to hang in there, some interesting engineering data is available on the web:

4a) Car resistance is much more complicated than just bearing friction/resistance. Car "resistance" sources include:

- Bearing "friction"

- Wheel/rail losses from the local compression of both the wheel tread and rail head as the wheel rolls along (the smallest "loss" term, since it does not involve friction. Often ignored)

- Wheel/rail friction – wheel flanges scraping the sides of railheads – this source of resistance is greater than modern RB's

- Grade (20 pounds resistance per ton, per percent grade – this is the physics of lifting the car up the hill and is unrelated to friction)

- Curvature

- Aerodynamic

4b) I found several resistance formulas. The Davis formula was the one I found most widely quoted. But different railroads appear to have formulated it with different terms. A CN document that discusses the change in their use of the equation over time is available for download:

http://5at.co.uk/uploads/Articles%20and%20papers/CANADIAN%20RESISTANCE%20PAPER.PDF

I recommend you read it if you want an introduction into the sources of train resistance - it is only 6 pages and does not overwhelm one with detailed equations. I would warn the reader to note the change in the definition of the term W over time. It can lead to some confusion when trying to follow the change in CN's application of the Davis equation over time(See footnote).

It makes for very interesting reading, and rather than my trying to compose a detailed summary of it, I will highlight one topic that appears authoritatively stated that has been discussed in this thread, and make an observation about how to interpret older bearing friction data:

When it comes to starting cars, the CN document recommends that 35 pounds per car ton be used as the starting resistance of a plain bearing equipped car when below freezing, and 25 pounds per ton above freezing! The same CN document suggests starting resistance for RB cars is 5 lbs per ton. But this includes ALL sources of resistance when starting a train.

The other observation from reading the CN document, it is that I am no longer sure how to interpret the 1931 Timken bearing test results in the ASME book I have been quoting. The vertical axis of the figure in the book is labeled "resistance", the horizontal axis is speed. The test was conducted with the PRR, and I have other PRR test reports that make it quite clear that the PRR test department was very much aware of aerodynamic losses. Plus the increase in resistance as speed increased, as shown in the figure, is gradual, and does not reflect the increase that would result from aerodynamics. So it appears aerodynamic resistance has been taken out of the data. Assuming the data was collected on level and straight track, that still leaves other sources of train resistance unrelated to bearings that need to be accounted for. For modern bearing cars, the primary source of resistance is now the tendency of trucks to wobble such that the wheel flanges come into contact with the sides of the rail head (truck "hunting"). The CN data reports that in the early 1990's this resistance was as high as 2.1 pounds per ton for a loaded car. So without access to the original test report, there is no way to know if the 1931 Timken bearing report, with the minimum resistance of 3.1 pounds per ton at 17 mph for plain bearings, and 2.6 pounds per ton minimum at 15 mph for RB equipped cars, is only reporting bearing resistance or all train resistance other than aerodynamic. Unless the full PRR/Timken report can be found, this will remain a mystery – did the 1931 Timken resistance data report only bearing resistance?

The CN document is through 1992, and there has been a lot of recent prototype research due to the increase in fuel costs and the desire of modern RR's to increase their cost competitiveness against trucks by reducing fuel consumption.

There are many interesting documents available on the web, but one recent presentation that also provide some interesting information about the scope of Intermodal rail shipments in the US is from BNSF:

http://ict.uiuc.edu/railroad/CEE/pdf/PPT%27s/fall08/Stehly_10-24.pdf

4c) Some general observations from this and several other sources –

- My engineering experience would suggest (but I cannot find this in an authoritative source) that in the STMFC era, plane journal bearing resistance was the dominant contributor to "rolling" resistance. With the significant reduction in bearing friction achieved by roller bearings, the other sources of friction have become much more evident. With today's fuel costs the RR's are working to reduce the friction from these other sources using new technologies. Top of rail lubricants, lubricants in curves, self steering trucks, and several other areas are the focus of funded research and equipment development, all to reduce rolling resistance. There has even been work to optimize double stack loading to reduce the aerodynamic drag induced by large gaps between each stack.

- Modern roller bearings exhibit almost constant "resistance" across the full speed range for freight trains. Most importantly, RB starting resistance is only slightly higher than rolling, and it is an order of magnitude less than plain journal bearing starting resistance. So steam locomotives in excursion service can now start the train they can pull!

- Surprisingly, it is hard to find published bearing rolling resistance data. I think because it is a problem the industry considers solved – bearings are standardized around the Timken AP2 taper concept. But BNSF did publish a number – an amazingly low 0.6 pounds resistance per car ton

4d) Modern friction reduction work – In addition to curve lubricants and top-of-rail (TOR) lubricants, there appears to be significant research into self steering trucks designed to reduce truck hunting, and in some cases, keep the axles of a truck in a curve pointing towards the center of the curve (the axles not parallel). There is data that suggest that the more modern self-aligning/self-steering trucks actually change the age old curve compensation of 0.04% grade equivalent for each degree of curvature, and cut it in half, or even more for some of the most advance trucks when operated in conjunction with rail lubrication systems. Some pretty wild stuff.

Once again savings from these more expensive trucks provide the most savings to the operator, so it seems like some of the most advanced freight car truck development is being applied to cars in captive service carrying heavy cargoes over many miles every day, and those cars being, you guessed it, coal hoppers – 60 years after C&O was the first to incorporate roller bearings into their hoppers. Déjà Vu.

Dave Evans

Footnote – within the CN document, the definition of the term W in the Davis equation changes. Note that the Davis formula produces the resistance in pounds per ton. So taking the value of R, and multiplying it by the trailing tons, yields the drawbar pull. In section 2.1.2, all Davis equations use W in weight (in tons) PER AXLE. In section 2.1.3.b, W is weight of the car. In 2.1.3.f, W is back to weight in tons per axle.


mopacfirst
 

I appreciate the engineering analysis that goes into subjects like this. ASME RTD continues to publish papers on improvements in this and related subjects, which are more generally referred to as 'truck-rail dynamics'.

But I will offer an anecdote.

In 1968 or 69, when I was still in high school, I traveled around town with a friend of mine who had a talent for trying things he shouldn't, like climbing on top of a boxcar to get a better view of the main line -- at 2 am. The security guard who saw us wasn't sympathetic in the least.

One Saturday, we were near an industry known as Southwest Grease which was served by the Santa Fe from the south end and MoPac from the north end. There was a track coming from the south end, which crossed a street and had loading docks adjacent, with a Santa Fe mechanical reefer spotted at the dock. (I know it was orange, and it was a Santa Fe car, so I'm pretty sure that would have meant it was an RPL.) This would have been a fairly new car with outside-post construction, so it would have to have had roller bearings.

Well, this guy got the bright idea to climb the car end and release the brake to see what would happen. The B end was the end away from the street, so no other bystander could see this. Sure enough, after a couple turns of the brakewheel, the car started to roll -- into the street. It got halfway into the two lane street, or about half its length, into the street before he got it stopped.

We got out of there real quick. Fortunately, this being Saturday, there were no vehicles passing on the street, which meant no witnesses.

Ron Merrick

--- In STMFC@yahoogroups.com, "Dave Evans" <devans1@...> wrote:
<snip>
All,

Begging the moderator's indulgence one last time, I wanted to wrap up my part of this thread <snip>


Frank Greene
 

On 10/14/2012 12:21 AM, Dave Evans wrote:
... 1b) The C&O cars included a fat white strip under part of Chesapeake and Ohio to indicate they were roller bearing equipped. Steve Lucas has a 1958 ETT that makes note of this mark, and instructs crews in special handling of RB equipped cars, since the slippery little devils will roll a lot more at low speeds than plain journal bearing equipped cars. It would be useful to know if other ETT's of the late STMFC era had similar notations, and if that might mean specific marks need to be included on 1950's STMFC models from railroads other than the C&O.

Scanning through several Southern Railway ETTs from 1954-'58 did not identify any special instructions for roller bearing equipped cars. On roller bearing equipped boxcars and covered hoppers, Southern Railway stenciled "[brand name] ROLLER BEARINGS" in 2 1/2" letters on the side sill near the right bolster.


2a)The limited deployment of RB's in the STMFC era had little impact on freight train performance, although it did impact some individual car handling tasks, such as the C&O ETT instruction to not hump RB equipped cars and apply special practices for spotting RB equipped cars. It would be interesting to know if other ETT's and/or rulebooks had similar rules/guidance.

Why not hump roller bearing equipped hopper cars?

--

Frank Greene
Memphis, TN


devansprr
 

--- In STMFC@yahoogroups.com, Frank Greene <frgreene290@...> wrote:

On 10/14/2012 12:21 AM, Dave Evans wrote:
... 1b) The C&O cars included a fat white strip under part of Chesapeake and Ohio to indicate they were roller bearing equipped. Steve Lucas has a 1958 ETT that makes note of this mark, and instructs crews in special handling of RB equipped cars, since the slippery little devils will roll a lot more at low speeds than plain journal bearing equipped cars. It would be useful to know if other ETT's of the late STMFC era had similar notations, and if that might mean specific marks need to be included on 1950's STMFC models from railroads other than the C&O.

Scanning through several Southern Railway ETTs from 1954-'58 did not
identify any special instructions for roller bearing equipped cars. On
roller bearing equipped boxcars and covered hoppers, Southern Railway
stenciled "[brand name] ROLLER BEARINGS" in 2 1/2" letters on the side
sill near the right bolster.


2a)The limited deployment of RB's in the STMFC era had little impact on freight train performance, although it did impact some individual car handling tasks, such as the C&O ETT instruction to not hump RB equipped cars and apply special practices for spotting RB equipped cars. It would be interesting to know if other ETT's and/or rulebooks had similar rules/guidance.

Why not hump roller bearing equipped hopper cars?

--

Frank Greene
Memphis, TN
Frank,

Thanks for checking the ETT's. Where is it written about the cars being labeled RB equipped? I wonder if it was an AAR rule? Or each railroad did their own thing?

At the low speeds of a hump yard, a roller bearing equipped car would roll much further, and could reach the string of cars at the end of the track at a much higher speed.

For an automatic retarder, I would expect the amount of retarding would need to be changed for a roller bearing equipped car versus a plain bearing equipped car (I think automatic retarders were already adjusting for car weight). Over on OpSig a professional railroader indicated that modern hump yard retarders now take wind speed/direction into account because the cars are so free wheeling.

I suspect it would also require very different handling by a hump rider manually controlling the brake (although one would expect quick adaptation if the riders were instructed in the difference.) Perhaps C&O was reacting to damaged cargo from too-high hump impacts, or possibly injuries to riders?

So I suspect the Southern RB marking was to at least help someone working a hump yard (retarder controls or riders - either one).

Were hump riders ever outlawed? Or did the railroads find them too expensive (in pay or in damaged contents)?

Dave Evans


richard haave
 

I believe the "No hump" was due to concerns about bearing
damage if couplings were harsh. The car end away for joint tends
to go straight up and then comes down hard on bearings. In
today's railroading if a loaded car (roller bearing of course)
is derailed the bearings on the derailed axles must be inspected
and/or changed due to the pounding the bearings absorb when
bouncing over ties, etc. Empty cars car go about half a car
length derailed before inspection needed.

Dick Haave
***************************



In STMFC@yahoogroups.com, "Dave Evans" <devans1@...> wrote:


--- In STMFC@yahoogroups.com, Frank Greene <frgreene290@> wrote:

On 10/14/2012 12:21 AM, Dave Evans wrote:
... 1b) The C&O cars included a fat white strip under part of Chesapeake and Ohio to indicate they were roller bearing equipped. Steve Lucas has a 1958 ETT that makes note of this mark, and instructs crews in special handling of RB equipped cars, since the slippery little devils will roll a lot more at low speeds than plain journal bearing equipped cars. It would be useful to know if other ETT's of the late STMFC era had similar notations, and if that might mean specific marks need to be included on 1950's STMFC models from railroads other than the C&O.

Scanning through several Southern Railway ETTs from 1954-'58 did not
identify any special instructions for roller bearing equipped cars. On
roller bearing equipped boxcars and covered hoppers, Southern Railway
stenciled "[brand name] ROLLER BEARINGS" in 2 1/2" letters on the side
sill near the right bolster.


2a)The limited deployment of RB's in the STMFC era had little impact on freight train performance, although it did impact some individual car handling tasks, such as the C&O ETT instruction to not hump RB equipped cars and apply special practices for spotting RB equipped cars. It would be interesting to know if other ETT's and/or rulebooks had similar rules/guidance.

Why not hump roller bearing equipped hopper cars?

--

Frank Greene
Memphis, TN
Frank,

Thanks for checking the ETT's. Where is it written about the cars being labeled RB equipped? I wonder if it was an AAR rule? Or each railroad did their own thing?

At the low speeds of a hump yard, a roller bearing equipped car would roll much further, and could reach the string of cars at the end of the track at a much higher speed.

For an automatic retarder, I would expect the amount of retarding would need to be changed for a roller bearing equipped car versus a plain bearing equipped car (I think automatic retarders were already adjusting for car weight). Over on OpSig a professional railroader indicated that modern hump yard retarders now take wind speed/direction into account because the cars are so free wheeling.

I suspect it would also require very different handling by a hump rider manually controlling the brake (although one would expect quick adaptation if the riders were instructed in the difference.) Perhaps C&O was reacting to damaged cargo from too-high hump impacts, or possibly injuries to riders?

So I suspect the Southern RB marking was to at least help someone working a hump yard (retarder controls or riders - either one).

Were hump riders ever outlawed? Or did the railroads find them too expensive (in pay or in damaged contents)?

Dave Evans