Are Piggyback Van Trains faster then Doublestack?

[MichaelSol]

For an 80 car, 7200 ton train with two six axles, here's the air resistance as a % of total train resistance (traction HP required to move train):

on the level:

10 mph - 17%  (143 HP)
30 mph - 46% (1466 HP)
50 mph - 60% (5162 HP)
70 mph - 68% (12418 HP)

TomDiehl:
No, it says that wind resistance of a train at the speeds they travelled was consuming a very small percentage of the power required to move the train, which is EXACTLY what I said.

TomDiehl:
"As big and heavy as any train is, the wind resistance is a very small factor."

I am sure Otto Kuhler is rolling over in his grave at the complete misrepresentation of his remarks by Tom Diehl. The interpretation placed by Diehl on Kuhler's remarks would make it appear that Kuhler did not believe there was much resistance from air density at higher speeds.

That interpretation is simply absurd.

In case there is any doubt, Diehl emphasized his remarks as being EXACTLY what he meant.

It is abundantly clear that Diehl is EXACTLY wrong on the point.

This is not the first time that TomDiehl has not just made an error [to err is human ...] but more disturbingly, it is not the first time that he has intentionally misrepresented the statements of an authoritative source as a cloak for his own strong, unfounded opinion or, as in the case of the steam-diesel thread, simply invented, wholesale, a variety of "studies" which he offered in support of his position, none of which he had ever even seen nor knew whether or not they actually existed. He simply made them up, as he made up Otto Kuhler's alleged belief that there was no such thing as air resistance, or that it was "negligble" as an impact on the overall power needed to move trains.

Hopefully that has been put to rest as the complete fallacy that it was and is.

What is clear from Don's figures is that, at 50 mph, 60% of the horsepower utilized at that speed is utilized overcoming the resistance caused by air density, and 40% of the horsepower utilized is utilized overcoming the resistance due to the weight of the train and the moving friction caused therefrom.

Without detailed specific cross sectional measurements, the following numbers from my spreadsheet are simply relative, but that the air drag or aerodynamic resistance of a standard boxcar at 50 mph is slightly less than COFC, but that air resistance for TOFC is approximately 89% greater than for a standard boxcar. and 65% greater than COFC. This is notwithstanding the fact that overall resistance of the COFC and boxcar are within 1% of each other, and the TOFC only 16% greater, in overall motion resistance, than a standard boxcar.

I am assuming Don's figures come from the AREMA Manual for Railway Engineering.

My notes are from AREMA, with a 2003 copyright.

"In general, rolling resistance of a train, R (in lb.), can be calculated using an empirical
expression as follows:

R = A + B V + C D V2

where A, B, C & D are coefficients defining the different resistive forces that are either independent, dependent or affected by the square of the train speed V.

Davis Formula

The first empirical formula to compute rolling resistance was developed by W.L. Davis in 1926. The original Davis formula provided satisfactory results for older equipment with journal bearings within the speed range between 5 and 40 mph. Roller bearings, increased dimensions, heavier loadings, higher train speeds and changes to track structure have made it necessary to modify the coefficients proposed by Davis. Since then, there had been various modifications. Interested readers may refer to Section 2.1 of Chapter 16 in the AREMA Manual for Railway Engineering for more information."

From the US Army Corp of Engineers, August, 2000
Analysis of Energy, Emission and Safety Impacts of Alternative Improvements to UMR-IWW, discussing railroad energy consumption:

"Air resistance varies approximately with the cross-sectional frontal area of the vehicle and the square of speed (Hay, 1982). It is affected also by equipment profiles and the potential for localized air disturbances in vehicle frontal areas and under frames. Trailer-on-flatcar (TOFC) shipments and automobile carriers or “autoracks” are thought to be especially problematic.[The term TOFC , as used in this report, encompasses container-on-flatcar (COFC) shipments on traditional flatcars. Double-stack container cars are considered as a separate category for purposes of energy analysis.]"

[MichaelSol]

OK, we've had some fun playing "where is it". 

Sol has left 'a couple' of things out, and they are things that go against his argument.  I've underlined words in his first paragraph that send us off in the wrong direction.

To understand why weight is a much more critical factor than "air resistance" we need to know that these two "resistance" factors are in the Davis formulas.  They relate to the weight and increase or decrease depending on....

For first place, be the first to name these two resistance factors AND thier values per ton of train. 

Well, I am curious where this is going ....

[oltmannd]

OK, we've had some fun playing "where is it". 

Sol has left 'a couple' of things out, and they are things that go against his argument.  I've underlined words in his first paragraph that send us off in the wrong direction.

To understand why weight is a much more critical factor than "air resistance" we need to know that these two "resistance" factors are in the Davis formulas.  They relate to the weight and increase or decrease depending on....

For first place, be the first to name these two resistance factors AND thier values per ton of train. 

Well, I am curious where this is going ....

The "A" term in the Davis Eq. is commonly known as "journal friction" - it is not weight related, "B" as "flange friction" - it is directly weight related, and C as "wind resistance" - which is not weight related.

For the hypothetical 7200 ton, 80 car train at 50 mph on the level, The journal friction is rougly 1000# , flange friction 11,000# and windage 19,000#.

But, on a 1/2 grade, the grade resitance - which is entirely weight related - is 76,000# - which is more than double the total rolling resistance at 50 mph.

So, is it weight or is it windage? 

It depends.....

But at least one can get a glimpse of the great cost of fast trains and ruling grades are such important determiners of which routes prosper and which fail......

[TomDiehl]

For an 80 car, 7200 ton train with two six axles, here's the air resistance as a % of total train resistance (traction HP required to move train):

on the level:

10 mph - 17%  (143 HP)
30 mph - 46% (1466 HP)
50 mph - 60% (5162 HP)
70 mph - 68% (12418 HP)

TomDiehl:
No, it says that wind resistance of a train at the speeds they travelled was consuming a very small percentage of the power required to move the train, which is EXACTLY what I said.

TomDiehl:
"As big and heavy as any train is, the wind resistance is a very small factor."

I am sure Otto Kuhler is rolling over in his grave at the complete misrepresentation of his remarks by Tom Diehl. The interpretation placed by Diehl on Kuhler's remarks would make it appear that Kuhler did not believe there was much resistance from air density at higher speeds.

That interpretation is simply absurd.

In case there is any doubt, Diehl emphasized his remarks as being EXACTLY what he meant.

It is abundantly clear that Diehl is EXACTLY wrong on the point.

This is not the first time that TomDiehl has not just made an error [to err is human ...] but more disturbingly, it is not the first time that he has intentionally misrepresented the statements of an authoritative source as a cloak for his own strong, unfounded opinion or, as in the case of the steam-diesel thread, simply invented, wholesale, a variety of "studies" which he offered in support of his position, none of which he had ever even seen nor knew whether or not they actually existed. He simply made them up, as he made up Otto Kuhler's alleged belief that there was no such thing as air resistance, or that it was "negligble" as an impact on the overall power needed to move trains.

Hopefully that has been put to rest as the complete fallacy that it was and is.

The only thing that was "misrepresented" in this thread was the claim that you had any idea what was being discussed for the first 2-1/2 pages.

On a level track, two SD90's would not be able to attain 70 MPH with the said train, simply because of wind resistance, which would require over 12,000 HP just for that?

So in the end you agree with me, that the difference in wind resistance between the double stack and the piggyback would not make one run slower than the other. I still find it hard to believe that wind resistance is a function of weight rather than amount and sizes of surfaces for the wind to act against?

Especially in light of Oltmannd's post.

[greyhounds]

The "A" term in the Davis Eq. is commonly known as "journal friction" - it is not weight related, "B" as "flange friction" - it is directly weight related, and C as "wind resistance" - which is not weight related.

For the hypothetical 7200 ton, 80 car train at 50 mph on the level, The journal friction is rougly 1000# , flange friction 11,000# and windage 19,000#.

But, on a 1/2 grade, the grade resitance - which is entirely weight related - is 76,000# - which is more than double the total rolling resistance at 50 mph.

So, is it weight or is it windage? 

It depends.....

But at least one can get a glimpse of the great cost of fast trains and ruling grades are such important determiners of which routes prosper and which fail......

Well, I'm going to declare a winner.  Congradulations!  You won!

I would have calculated the extra resistance due to a 0.5% grade on a 7,200 ton train at 72,000 not 76,000 pounds - but that's splitting hairs.  And don't forget the curves.  My information says they add 0.8 pounds of resistance per degree of curvature for every ton the train weighs.  So, using the numbers above, a 7,200 ton train going up a 0.5% grade on a one degree curve would have to overcome 108,760 pounds of resistance as opposed to only 31,000 pounds resistance on straight level track.

That slight grade and curve more than tripple the resistance - and the increase is all weight related.

Since trains go up hills and around curves, it is clearly evident that what Tom was saying is very accurate.  With good streamlining you maybe could reduce the air drag by, let's be generous, 35%.  In this case that would be around 6,650 pounds - that's just a little more than the curve adds.  You'd save about 6.1% of the resistance.

It's more important to reduce train weight - go to lightweight equipment, aluminum gons, skeleton flats for TOFC/COFC, etc.  Just like the designers of the streamliners did.

Tom was/is right.  The lightweight equipment was more important than the cosmetic streamlining. BTW, it also could be accelerated/decelerated faster.

Sol pretty much left the whole grade/curve thing out.

 

 

[MichaelSol]

Well it is true that trains go uphill and the weight vector increases relative to the aerodynamic drag.

It is true the increase in motion resistance is all weight related.

But then they go downhill and the weight vector decreases relative to the aerodynamic drag. Kind of left that part out, Strawbridge. Why?

But then it is true that the decrease in motion resistance is all weight related.

And of course Strawbridge's statistical tomfoolery would like to propose that the grade goes on forever, rather than the likelihood of it being a small part of any hypothetical route mileage. However, if the grade is 40 miles long on a 400 mile run, the net effect is to add 7,200 lbs to the total average resistance, not 72,000 lbs. The Strawbridge sleight of hand disguises the fact that the average rolling resistance of the run will increase by 18% at 50 mph, rather than over 200%.  The percentage of motion resistance attributable to aerodynamic drag drops from 60% to just over 50%. While this example assumes no negative grades on the run, which would cancel out the Strawbridge scenario, it does underscore how important that continuous aerodynamic drag is -- because it is continuous.

It is also true, however, that  the wind blows. Sometimes it is a headwind and increases the aerodynamic drag. In that case the increase in motion resistance is all aerodynamic drag related.

And sometimes it is a tailwind and decreases the effect of the aerodynamic drag.  In that case, the decrease in motion resistance is all aerodynamic drag related.

The interesting point about streamlining is that it would provide an advantage regardless of grade or curvature. Strawbridge didn't mention that either. And, his example carefully assumes the grade is uncompensated. 

In general, however, where it is safe to say that motion resistance related to weight can go up or down depending on grade -- and of course trains do go downhill -- the average happens to resemble flat ground -- zero grade. Likewise, the average impact of changes in air "pressure" or density due to wind over all train movements is likely to be zero.

Choosing a specific set of assumptions to meet the pre-determined conclusion will indeed give you the results that you wish, but only if you ignore completely the conditions which produce the opposite effect. That's called cherry picking.

Of course unless you grew up in Bill Cosby's neighborhood where the road to school was uphill... both ways.

I am sure Strawbridge believes what he says. No doubt the Illinois Central was uphill ... both ways. Forever.

It is also true that curvature increases friction in a proportion to the weight of the car.  Assuming you can get the entire 7,200 ton train on a 2 degree curve at once, you would indeed incur a resistance of 11,520 lbs.

Illinois Central must have had some mightly long impressive curves.

Even at that, at 50 mph, assuming the train is on one huge continuous 2 degree curve constantly, the aerodynamic drag is just slightly less than half of the total motion resistance, but at 70 mph, even with Strawbridge's unusual railroad, aerodynamic drag is still the major source of motion resistance. And at 1 degree, 50 mph, aerodynamic drag is still the largest source of resistance to the locomotive.

More realistically, at 50 mph, if 20 car lengths are on the curve, the impact is 2,880 lbs, and does not change the fact that, at that speed, the majority of the resistance that the locomotive must overcome is still created by aerodynamic drag. If you postulate that the train encounters such curvature over 20% of its run, then the equivalent impact is 576 lbs on the average, where windage equals 19,000 lbs, and which shifts the average velocity threshold at which aerodynamic drag exceeds all other motion resistance up by less than 1.0 mph. Hardly signficant. Yup. "Sol pretty much left it out." So does the typical Davis formulation, for obvious reasons.

Is that 2% change in average resistance due to curvature signficant compared to the effect of continuous aerodynamic drag at 58% -60% at 50 mph?

This was a nice try at twisting and distorting facts to prove a point, but on closer examination, the effort obviously fails unless you can accept Strawbridge's sleight of hand that postulates 1) that railroads only go uphill, and 2) that railroads are continuous curvature.

In leaving out the effect of wind, apparently he also adopts Diehl's scientific theory that the wind has no effect -- that it is just the same thing as "air." Quite a pair.

[GP40-2]

This thread is better entertainment than watching two white-trash trailer park chicks from Montanna duke it out on the Jerry Springer Show...

Pluuueeeese don't stop. I'm done with work, and I have all weekend to laugh at this...

[greyhounds]

Illinois Central must have had some mightly long impressive curves.

Actually, we did.  The IC had the longest continuous curve in the world.  It went through the bayou around Lake Ponchatrain into New Orleans.  It was miles long. 

If you don't understand that grades and curvature are significant factors in rail operations and that "Wind Resistance" is an afterthought, you're beyond any possible reason.

The most significant resistance factor is the grade.  You can either pile on the power or reduce the tare weight to deal with the grades  The world isn't flat. The streamliner designers recognized that reducing weight had more benifits than reducing "wind resistance".

[erikem]

Actually, we did.  The IC had the longest continuous curve in the world.  It went through the bayou around Lake Ponchatrain into New Orleans.  It was miles long. 

Longer than the curve on the Espee (now UP)  main-line south of Phoenix? That's several miles of 10 minute  (1/6 degree) curve. Asking more out of curiosity than disagreement.

The most significant resistance factor is the grade.  You can either pile on the power or reduce the tare weight to deal with the grades  The world isn't flat. The streamliner designers recognized that reducing weight had more benifits than reducing "wind resistance".

True for the speeds achieved by typical American passenger trains - emphatically not true for very high speed trains such as the TGV - they need so much power to overcome aero drag that 3% grades area piece of cake.

The first generation of American streamliners did benefit from streamlining along with being very lightweight. Later trains were heavier and thus benefitted less from streamlining.

[greyhounds]

Actually, we did.  The IC had the longest continuous curve in the world.  It went through the bayou around Lake Ponchatrain into New Orleans.  It was miles long. 

Longer than the curve on the Espee (now UP)  main-line south of Phoenix? That's several miles of 10 minute  (1/6 degree) curve. Asking more out of curiosity than disagreement.

The most significant resistance factor is the grade.  You can either pile on the power or reduce the tare weight to deal with the grades  The world isn't flat. The streamliner designers recognized that reducing weight had more benifits than reducing "wind resistance".

True for the speeds achieved by typical American passenger trains - emphatically not true for very high speed trains such as the TGV - they need so much power to overcome aero drag that 3% grades area piece of cake.

The first generation of American strhttp://www.railwaystation.com/1942/02.htmleamliners did benefit from streamlining along with being very lightweight. Later trains were heavier and thus benefitted less from streamlining.

Yes, I believe it was longer.  I didn't remember the exact length - that's why I didn't state it.  I like to be sure of my facts.  But, according to #48 in this thing:

http://www.railwaystation.com/1942/02.html

It was 9.45 miles without a straight piece of rail.  In latter years there was a realingment that broke the curve in two.

Steamlining does have benifits.  But they pale in comparison to reducing the weight you have to drag up a hill.  This is especially true in passenger trains where most of the weight is in the equipmnt, not the payload.

The HP/ton ratio on the TGV has to be very high.  (or is it KW/Kilo ratio?)

[Hugh Jampton]

HOLD YER FIRE!!!!!!!!

Actually it's kW/metric tonne, but I've converted to hp/ton for you
TGVs have a hp/t ratio varying between 24 to 28 depending on the model
.

Carry on.........

[CSSHEGEWISCH]

HOLD YER FIRE!!!!!!!!

Actually it's kW/metric tonne, but I've converted to hp/ton for you
TGVs have a hp/t ratio varying between 24 to 28 depending on the model
.

Carry on.........

With that kind of horsepower/ton ratio, I would be extremely disappointed if TGV's didn't handle 3-4% grades like they weren't there or fail to accelerate from a stop like a top-fuel dragster.  It would be interesting to find out the number of substations required to support that kind of current draw.

[n012944]

. Also you did look up in this thread of a BNSF stacker being paced at 70MPH? .   

 

Most pig trains on the BNSF are powered with a high hp/ton ratio, to ensure that the train can maintain 70MPH.  Stack trains on the other hand, have a lower hp/ton ratio, and while they are authorized to do 70MPH, and will, they will not be able to accelerate to 70 as quickly or maintain it as long.  So while I am sure that you did pace a stack train at 70, it has little to do with the first question.

 

Bert

[MichaelSol]

If you don't understand that grades and curvature are significant factors in rail operations and that "Wind Resistance" is an afterthought, you're beyond any possible reason.

The most significant resistance factor is the grade.  You can either pile on the power or reduce the tare weight to deal with the grades  The world isn't flat. The streamliner designers recognized that reducing weight had more benifits than reducing "wind resistance".

Of course all of this explains why cars are getting heavier and trains longer and heavier. Nobody listens to Strawbridge.

No one here has disagreed with the notion that a lighter train is easier to pull. Good grief. Talk about a straw argument. Nobody says that grades do not add resistance. But grades (downhill) also reduce resistance and that's the part of the equation you don't seem to get.

Perhaps that's why variations of the Davis Algorithm often leave that part of the equation off.

Over the entire cycle of a run, back to the starting point, the total effect will be close to zero. Get that, zero.

Of course, the irony of the Strawbridge argument is, the lighter the train, the greater the effect of aerodynamic drag. It goes up. Poor Tom Diehl, he was not only completely unaware that aerodynamic drag would account for 60% of the locomotive power used at 50 mph, if the train were lighter, that percentage would go up!

The point still being, and the point that was originally in contention,

TomDiehl:"As big and heavy as any train is, the wind resistance is a very small factor."

It is not, in fact, "a very small factor" at higher speeds.

I think that notion has been exposed for the fallacy that it was.

Yes, you can invent a whole series of conditions to impose on a train. For some reason you just can't accept the fact that Diehl happened to be dead wrong on the point. As true as your conditions might be under a variety of circumstances, the math still shows that they don't rebut the fact that, at higher speeds, aerodynamic drag is a significant factor.

You can run the train uphill, and you can run the train downhill. You can take it around curves. The problem is, at higher speeds aerodynamic drag remains the most most significant factor as it does for any moving object at the Earth's surface.

And you can postulate a train that only runs uphill, only on curves, and only on Tuesdays, and it doesn't change that fact that for trains in general, aerodynamic drag is a significant factor at higher speeds.

Are you trying to prove it isn't?

You fail. It is.

Are you trying to show there are circumstances under which it might not be true? No one says there aren't, although the math under reasonable circumstances seems to work against your proposal.

But, you have stumbled onto an interesting conundrum ... for another post. 

[spbed]

Were those Hi HP loocos or low HP locos on that train I paced?

 

. Also you did look up in this thread of a BNSF stacker being paced at 70MPH? .   

 

Most pig trains on the BNSF are powered with a high hp/ton ratio, to ensure that the train can maintain 70MPH.  Stack trains on the other hand, have a lower hp/ton ratio, and while they are authorized to do 70MPH, and will, they will not be able to accelerate to 70 as quickly or maintain it as long.  So while I am sure that you did pace a stack train at 70, it has little to do with the first question.

 

Bert

[GP40-2]

Hey MichaelSol,

After relaxing a bit from a hectic work week, I decided to play nice. I agree using the word "stole" was a bit extreme. But,  I  found the similarities between your statements and the linked web page amusing to say the least.

One other thing: The rest of you guys who are fighting with MichaelSol concerning his specific statements about air resistance and speed are wasting your time.

[MichaelSol]

But,  I  found the similarities between your statements and the linked web page amusing to say the least.

"Similarities?"

You mean the single reference in the sixth post on the matter to "2500 hp"? After three posts using completely different information? 

Yup, I had to go looking on websites to come up with a horsepower number. Couldn't think of one on my own.

Pay attention next time.

In any case, the numbers used, as I stated at the outset, come from the Davis Equation. Horowitz, to my knowledge, does not have an equation of his own, and if he does, I don't know what it is. Simply nothing really to beg, borrow or steal from Horowitz, it's not his equation. And I did not attribute it to him, I specifically stated that the results were generated by the Davis formula. Regarding the Davis Equation or its related progeny, it is neither my theory nor does it matter if I or anyone else agrees with it or not. But if you don't, what's your substitute? A wild guess?

"The first train resistance models by Schmidt and Tuthill (1910-1940's) were developed at UIUC. These findings ultimately led to the Davis Equation for estimating train resistance which is still in use today." Overview of the UIUC Railroad Research Program: A Century of Progress in Railroad Engineering Research at UIUC .

[NW_611]

I think the "second generation" (my rough classification) TGV trainsets like the Atlantique and Reseau pretty much glide up those grades like they weren't there. I read somewhere, probably at TGVweb, that the trains' abilities to ignore various grades made for considerable economies during the construction of the LGV system. After all, when you take a hill at a speed north of 150MPH, a percent or two of incline might mean "Oh darn, we dropped two or three miles/hour; time to notch back up!"

I'm not sure what the electrical infrastructure requirements are; I'm under the impression that all of the LGV system is run off the French nuclear system anyways. As for outrunning someone in Top Fuel eliminator competition, I think Doug Kalitta might be faster from the station stop, but SNCF probably wins in passenger comfort and carrying capacity.

[MichaelSol]

Steamlining does have benifits.  But they pale in comparison to reducing the weight you have to drag up a hill. 

"Steamlining" is a passenger train argument, I don't know why it keeps popping up here. It would make an interesting thread of its own, but its just not relevant to freight at freight speeds. Maybe it is, but not much.

However, with regard to freight, the poster contends that "steamlining" benefits pale in comparison to reducing the weight you have to drag up the hill.

Reality check for Strawbridge: no one is reducing the weight of the trains you have to drag up the hill. Hasn't happened in 150 years. They keep getting heavier.

Strawbridge has completely misstated what has happened. Railroads did not reduce weight, they increased power. A completely different approach.

And three things made it possible to handle heavier trains.

1) Increased power.

2) The characteristics of the electric traction motor and electric transmission that permits maximum tractive effort at lower speeds.

3) The use of lower speeds to reduce the aerodynamic resistance.

To paraphrase Secretary Rumsfeld, " you are stuck with the train weight you've got, not the train weight you would like to have."

And as Strawbridge cleverly pointed out, that train weight works to the disadvantage of the railroad on a grade.

What happens?

Strawbridge says you have to reduce weight.

You can't. Well you can, but you don't want to if you don't have to.

But, you can change the aerodynamic resistance.

Take Strawbridge's 72,000 lb increased resistance at 50 mph on the 0.5% grade as an example. If the available tractive effort at 50 mph is only 50,000 lbs, there's a problem. Well, you drop to 10 mph. Aerodynamic resistance drops nearly 30,000 lbs. Tractive effort goes up over 100,000 lbs.

Strawbridge wants to reduce weight. That 30,000 lbs of power available from reducing aerodynamic drag is the equivalent of 50 boxcars of that 80 boxcar train, at 50 mph. Which would you do -- drop the weight, or keep the train intact and lower the aerodynamic resistance?

The fortuitous ability to reduce aerodynamic drag is much, much more significant than any feasible means of reducing that much weight. Aerodynamic drag is not only important as a resistance factor at higher speeds, it becomes an important reservoir of available power by lowering speed.

Between TE increases, and aerodynamic drag reductions, a lower maximum speed exists where the train can get up the hill.

Strawbridge and Diehl talk about reducing weight. Strawbridge even talks about looking for lower "tare" weights, as though the train and the laws of physics know the difference.

Pure baloney.

The "solution" is not and never has been reducing weight in freight service to achieve operating improvements (we are not talking revenue efficiency of higher cap versus lower cap cars).

Weights have been increasing and will presumably continue to increase.

The talk of reducing weights to increase train performance is a passenger train analogy that has absolutely no relevance to the freight rail industry.

And the weight in any case is not going to change on an existing train.

What has happened is that railroads utilize the substantial savings in aerodynamic drag, coupled with increases in tractive effort, at lower speeds, to continue to move ever heavier trains, day in and day out.

This is the interesting conundrum to the posters' insistence that gains can only come from less weight. It hasn't, isn't, and won't be happening. Pure fantasy.

But railroads have, for a long time now, been raising and lowering aerodynamic resistance to overcome flange friction from the weight of trains -- on flat ground, on grades, and on curves.

Every day. Every train.

Fortunately for the rail industry, Strawbridge has it wrong, backwards, and upside down. They don't need to lower the weight of cars and the train. They can lower the aerodynamic resistance which is exactly what they have, in fact, been doing when they go up a grade or around a curve.

[GP40-2]

 Regarding the Davis Equation or its related progeny, it is neither my theory nor does it matter if I or anyone else agrees with it or not. But if you don't, what's your substitute? A wild guess?

No need for me to guess at anything when I spend 60+ hours a week on my job using real world empirical data concerning subjects such as this.

That's the main difference between people in the industry like myself and foamers like you. You can write all the silly spreadsheets you like, and quote all the theory you want, but the fact is real world data trumps it all.

Honestly, have any of you really wondered why nobody who works in the industry takes anything posted on this forum, or any fan forum, seriously?

But my-oh-my,  it sure is funny watching all you foamers get your panties twisted up over this stuff.

[Anonymous]

Greenbrier and Gunderson are making Light Wieght Aluminum Coal Cars....

Must be a reason for this. The fuel savings on a 100 car 10,000 ton freight train?

Also I have seen Allunimun Hoppers....So it is only a a matter of time before we have Allnimim Intermodal Flats..

[MichaelSol]

 Regarding the Davis Equation or its related progeny, it is neither my theory nor does it matter if I or anyone else agrees with it or not. But if you don't, what's your substitute? A wild guess?

No need for me to guess at anything when I spend 60+ hours a week on my job using real world empirical data concerning subjects such as this.

That's the main difference between people in the industry like myself and foamers like you. You can write all the silly spreadsheets you like, and quote all the theory you want, but the fact is real world data trumps it all.

Honestly, have any of you really wondered why nobody who works in the industry takes anything posted on this forum, or any fan forum, seriously?

But my-oh-my,  it sure is funny watching all you foamers get your panties twisted up over this stuff.

Good for you. Glad you got it off your chest.

[Hugh Jampton]

user="BuyCSXrailroadStock!"]

Greenbrier and Gunderson are making Light Wieght Aluminum Coal Cars....

Must be a reason for this. The fuel savings on a 100 car 10,000 ton freight train?

Also I have seen Allunimun Hoppers....So it is only a a matter of time before we have Allnimim Intermodal Flats..

Not fuel savings. With coal for every pound you remove from the tare weight of the vehicle it allows an extra pound of coal, given that railroads are limited by the axle load.
Intermodal cars don't even come close to reaching the limit, and until they rais the maximum load of a comtainer to the point where aluminum cars become necessary they'll be made of goos old cheaper steel.

[TomDiehl]

Steamlining does have benifits.  But they pale in comparison to reducing the weight you have to drag up a hill. 

"Steamling" is a passenger train argument, I don't know why it keeps popping up here. It would make an interesting thread of its own, but its just not relevant to freight at freight speeds. Maybe it is, but not much.

However, with regard to freight, the poster contends that "steamlining" benefits pale in comparison to reducing the weight you have to drag up the hill.

And as Strawbridge cleverly pointed out, that train weight works to the disadvantage of the railroad on a grade.

Strawbridge and Diehl talk about reducing weight. Strawbridge even talks about looking for lower "tare" weights, as though the train and the laws of physics know the difference.

Pure baloney.

The use of the term "Streamlining," however it is spelled or misspelled in this thread, was my fault for bring in a somewhat related analogy to the original question. I should know better than to confuse the simple minded on this board.

I don't recall any place I talked about reducing the weight of the train, however, as you state  Strawbridge (and many others) have, talked about reducing tare weight. This is not so much related to the Operating Department of the railroad (why it would be related to the laws of physics, you'll have to explain) as it is to the Billing Department. If we assume that axle load limits remain the same, any reduction in tare weight will correspond to an equal increase in payload weight for that given car. To paraphrase your statement, the axle load limit doesn't care if it's tare weight or payload weight, but since most shipping charges are based on the weight of the cargo, that car can now haul more payload weight.

[spbed]

When DS cars 1st came out they were said to be more fuel efficent then TOFC cars in case you were unaware of that. The hype was that the DS steel wheel resistance to the rails was less then TOFC cars cause they were articulated 

 

But,  I  found the similarities between your statements and the linked web page amusing to say the least.

"Similarities?"

You mean the single reference in the sixth post on the matter to "2500 hp"? After three posts using completely different information? 

Yup, I had to go looking on websites to come up with a horsepower number. Couldn't think of one on my own.

Pay attention next time.

In any case, the numbers used, as I stated at the outset, come from the Davis Equation. Horowitz, to my knowledge, does not have an equation of his own, and if he does, I don't know what it is. Simply nothing really to beg, borrow or steal from Horowitz, it's not his equation. And I did not attribute it to him, I specifically stated that the results were generated by the Davis formula. Regarding the Davis Equation or its related progeny, it is neither my theory nor does it matter if I or anyone else agrees with it or not. But if you don't, what's your substitute? A wild guess?

"The first train resistance models by Schmidt and Tuthill (1910-1940's) were developed at UIUC. These findings ultimately led to the Davis Equation for estimating train resistance which is still in use today." Overview of the UIUC Railroad Research Program: A Century of Progress in Railroad Engineering Research at UIUC .

[Anonymous]

The Acticulation in practice means ....

1. Less Damage to Freight because of Slack Action.

2. Smother Starts and Stops...

3. In Practice....Less side to side action

4. I do remember seing articulated flats on TOFC so they are out there..

------The Lower profile of the TOFC does mean less wind resistance however the debate here seems to be if there shere HULK and BULK and WEIGHT really matter in the game here... On the CSX NYC water level route wind restiance is going to bve greater going west so the game there woul dhave to be figured out.

[erikem]

Those with long mmeories may recall Kneiling's arguments favoring COFC over TOFC - one being lower tare weight and the other being lower aero drag. I would suspect that a given length of DS cars will have higher drag than the same length of TOFC, but not twice the drag. I would also guess that the drag of DS cars loaded with 53's on top and 40's in the well would be less than with 40's on top. One of the big sources of drag on most trains is the gap between the cars - hence the full width diaphragms on the early streamliners.

The AT&SF had 5 and 10 trailer "Fuel-foilers" in the late 1970's which were the precursors to the DS cars.

[greyhounds]

Well, where do I start with this piece of .....

Reality check for Strawbridge: no one is reducing the weight of the trains you have to drag up the hill. Hasn't happened in 150 years. They keep getting heavier.

Strawbridge has completely misstated what has happened. Railroads did not reduce weight, they increased power. A completely different approach.

No, you're wrong agiain.  They've reduced weight.  What do you think aluminum gondolas do?  Double stack reduced the tare weight necissary to cary loads by 11% and TOFC spine cars eliminated the solid steel deck found on conventional intermodal flats.  They did this to reduce train weight. 

Now I'll grant you they replaced the reduced tare with payload, but that's OK - since they get paid for moving that stuff. They don't get paid for dragging freight cars around.

.Strawbridge even talks about looking for lower "tare" weights, as though the train and the laws of physics know the difference.

The "laws of physics" may not care, but the profit and loss statement does care.  Every dime a railroad spends dragging excess tare weight up a hill, and retarding it down a hill is a dime lost.  And the dimes add up real quick. 

Weights have been increasing and will presumably continue to increase.

The talk of reducing weights to increase train performance is a passenger train analogy that has absolutely no relevance to the freight rail industry.

Sol's inability to diferintiate between "good weight" and "bad weight" shows his ignorance.

"Good weight" is what the railroad is paid to move.  "Bad weight" is what the railroad has to put under the "good weight" in order to move it.  The goal is to decrease the bad weight and increase the good weight.  Sort of like cholesterol.  Railroads have continually strived to reduce the "bad weight", by reducing the amount of tare needed to cary a given amount of freight.  Sol aparently doesn't understand any of this. 

Fortunately for the rail industry, Strawbridge has it wrong, backwards, and upside down. They don't need to lower the weight of cars and the train. They can lower the aerodynamic resistance which is exactly what they have, in fact, been doing when they go up a grade or around a curve.

Nope, Sol's wrong again.

They gave up on streamlining and concentrated on reducing tare weight.  That's where the payoff is.

[broncoman]

Getting something from point A to point B isn't all about top speed or wind drag. It's all about priority. Priority is determined by service levels. Most of your TOFC trains are going to be classified as "Z" trains; high priority intermodal. The BNSF has the ZWSPNBY9/ZNBYWSP9 (Western Springs, IL - North Bay, CA) and the ZWSPRCH9/ZRCHWSP9 (Western Springs - Richmond, CA). The "9" on the end designates that as the highest priority "Z" train and the highest priority train running on the Transcon. Anythin with a "9" on the end is usually going to be a lot of UPS trailers. They pay the big bucks to get their trailers from one spot to another faster than other freight. A stack train might be authorized for the same speed as the "Z" train, 70 mph, but when the stack train is sitting in the hole for twenty minutes waiting for the "Z" to clear the main it isn't doing 70mph (not to mention the reduced speed getting into/out of the siding).

CC

Just a question with regards to what the difference is between Richmond and North Bay in the above desigantions?  I thought that BNSF loaded in Richmond and UP loaded in Alameda. 
Any enlightenment Chad?

Actually I have a second question, without getting into hypotheticals, does anyone know why Roadrailers work when the little single axle Trailer Train cars where taken out of service (unless someone has seen one recently)?
I imagine that the little cars didn't have enough weight to them when they were in mixed used while the Roadrailers are a unit type train/car.

Dave

[MichaelSol]

Well, where do I start with this piece of .....

Reality check for Strawbridge: no one is reducing the weight of the trains you have to drag up the hill. Hasn't happened in 150 years. They keep getting heavier.

Strawbridge has completely misstated what has happened. Railroads did not reduce weight, they increased power. A completely different approach.

No, you're wrong agiain.  They've reduced weight.  What do you think aluminum gondolas do?  Double stack reduced the tare weight necissary to cary loads by 11% and TOFC spine cars eliminated the solid steel deck found on conventional intermodal flats.  They did this to reduce train weight. 

Now I'll grant you they replaced the reduced tare with payload, but that's OK - since they get paid for moving that stuff. They don't get paid for dragging freight cars around.

.Strawbridge even talks about looking for lower "tare" weights, as though the train and the laws of physics know the difference.

The "laws of physics" may not care, but the profit and loss statement does care.  Every dime a railroad spends dragging excess tare weight up a hill, and retarding it down a hill is a dime lost.  And the dimes add up real quick. 

Weights have been increasing and will presumably continue to increase.

The talk of reducing weights to increase train performance is a passenger train analogy that has absolutely no relevance to the freight rail industry.

Sol's inability to diferintiate between "good weight" and "bad weight" shows his ignorance.

"Good weight" is what the railroad is paid to move.  "Bad weight" is what the railroad has to put under the "good weight" in order to move it.  The goal is to decrease the bad weight and increase the good weight.  Sort of like cholesterol.  Railroads have continually strived to reduce the "bad weight", by reducing the amount of tare needed to cary a given amount of freight.  Sol aparently doesn't understand any of this. 

Fortunately for the rail industry, Strawbridge has it wrong, backwards, and upside down. They don't need to lower the weight of cars and the train. They can lower the aerodynamic resistance which is exactly what they have, in fact, been doing when they go up a grade or around a curve.

Nope, Sol's wrong again.

They gave up on streamlining and concentrated on reducing tare weight.  That's where the payoff is.

Typical.

Tare weight changes have not affected axle loadings, which is what the Davis Algorithm (and the laws of physics), have to measure as resistance contributors.

I have re-read this thread in vain for anyone even remotely attempting to argue that improving tare to payload ratios is not a good thing. No where. But that doesn't have a thing to do with the physics of journal, flange and drag resistance.

Why don't we just say it is easier to raise rates?

A completely straw man argument. Or ... perhaps a completely Strawbridge argument.

Good one Strawbridge, you invented your own controversy, came to your own party, and won lone-man bingo contest.

At the end of the day, overcoming aerodynamic drag is the single biggest use of horsepower from a locomotive, or any other motion machine, at higher speeds, and becomes progressively so at progressively higher speeds.

Took five pages to overcome the "resistance" to a well-established, well-understood principle by the usual suspects. No wonder "discussions" on this forum go haywire. Interesting bunch.