you seem to be saying the later Y6 had more starting TE than the early Y6. What's the connection between the two changes?"
BTW, this vast amount of lead was one of the things that the scrapyards bought the retired engines for.
BTW Pt. Deux,I noticed the other day that the subject (Re: ) of this entire post has changed names quite a few times over the now four pages. How does this take place when everything is still under the original title?
BTW Pt. Trois,Not to get this post even more off subject, but, Some of you have obviously read "The Steam Locomotive" by Ralph Johnson of "Baldwin" fame. No doubt that is where some of these formulas are coming from. But, have you noticed in the book the conspicuous absence of anything about a "Compound" locomotive (other than the one or two formulas) ?
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re: "Reportedly, Jeffries says N&W shortened cutoff on the later Y6s-- you seem to be saying the later Y6 had more starting TE than the early Y6. What's the connection between the two changes?"
All of the Y6's (and maybe the Y5's) originally were rated for a simple starting TE of about 152,000 lb (yes, even the Y6b's, with the thicker tires and other improvements). Various changes improved HP at speed and other properties, but AFAIK there was only one increase in tractive effort, to a simple starting TE of about 170,000 lb.
As best as I can recall right now (brain gone foggy!), the valve reworking did two (at least somewhat) related things, (1) decreasing the maximum cutoff and (2) increasing the valve efficiency (in a general sense). To speculate on top of a hazy memory, it may well have been that the improved valves allowed a coeficient higher than 0.85, in other words, for more of the stroke, your pressure in (all, in simple) the cylinders more nearly approached the 300 psi boiler pressure. Presumably this more than made up for the lack of additional steam being admitted between 80% and 90% etc.
Frankly, IMHO the Jeffries book does a somewhat less than stellar job of explaining and commenting on the sources and realities of the supposed increase in starting TE to around 170,000 lb simple. This is the kind of issue where I would love to hear the views of somebody like Parker Lamb. In fact, let's see whether he can be enticed . . .
The N&W timetable rated the A at 12500 tons up the 0.3% to Kingston (Ohio). No idea whether they actually did that-- but if they did, you figure anytime speed dropped below 5 mph on the 0.3% they were doomed to stall?
Normally a loco should be able to start a train of a listed tonnage rating. That's the way it is today and I have no reason to believe things were any different back then. If not, what good would the tonnage rating be in the fist place!
Even though the ruling grade on my district is from 1.6% to 1.64%, there are places that appoach 1.8%. However, they are short and though it may slow you down, it won't normally make you stall. You certainly wouldn't want to stop there with full tonnage or for that matter on top of a rail greaser.
The locomotive engineering section in the first edition of N&WGofS runs from p59 to p83. Cutoff modifications are discussed from p66 to p70. The figures are written out so they're hard to find - original cutoff, p66 first column; modified cutoff, p70 first column.
The modified Y6's had a higher TE and DB pull than the originals. See graphs on pgs 76 and 83.
feltonhill wrote:Timz, I believe your method uses an estimate of MEP directly?
It's not "my" method-- it's the often-used formula for a compound Mallet, which assumes
HP MEP + LP MEP = 85% of boiler pressure
HP TE = LP TE (so HP MEP = LP MEP times the square of (LP cyl bore/HP cyl bore) )
feltonhill wrote:I use an overall adjustment factor (s) and Jeffries' book uses percent cutoff. Whether they correlate or not, I don't know.
Reportedly, Jeffries says N&W shortened cutoff on the later Y6s-- you seem to be saying the later Y6 had more starting TE than the early Y6. What's the connection between the two changes?
(I don't see that in the original edition of Jeffries-- it's in the newer edition?)
I'm not ignoring this discussion, just got bogged down on some other stuff today.
The above percentages are correct as stated. However, I use an overall adjustment factor (s) and Jeffries' book uses percent cutoff. Whether they correlate or not, I don't know.
My method uses the standard tractive effort formula for each engine, a boiler pressure of 300 psi and a receiver pressure of 125 psi starting and 84 psi compound. These adjustment factors attempt to take into consideration the pressure losses from boiler to steam chest, and the effect of valve timing on MEP. I use the rated TE as a target value for the two equations and attempt to get a reasonable balance between the HP and LP engines at starting.
Timz, I believe your method uses an estimate of MEP directly?
I have this in a spreadsheet, but it's not possible to post it here. I'll try to summarize it in text format and post it.
feltonhill wrote:According to my estimates, and that's all they are, the as-built Y6's had valve timings that reflected an adjustment factor of about 74%. The final Y6b's and the improved Y6's were closer to 82%.
dredmann wrote:the Y5/Y6 originally allowed steam admission over, IIRC, 90% of stroke in the HP cylinders and 88% in the LP cylinders ... the new maximum cutoffs were 80% and 75%.
Do those agree?
erikem wrote:If the train can't start at 10 lb/ton on level track, it certainly couldn't go up a 0.3% grade.
timz wrote: erikem wrote:a circa 1920 Baldwin publication that shows the minimum rolling resistance for a passenger train as 4.5 lb/ton at 8 to 10 MPH. The 0 MPH intercept on the graph appears to be 15 lb/ton, 2 MPH looks to be about 10 lb/ton, 5 MPH is about 6 lb/ton.Supposedly N&W A's took 12500 tons [unassisted] to Columbus, climbing an 0.3% grade a few miles long, and C&O 2-10-4s supposedly took 13500 tons [unassisted] on their 0.2% grades to Columbus. Think it would be hopeless for either one of them to restart if they happened to get stopped on the ruling grade? Come to think of it, if rolling resistance were 10 lb/ton at 2 mph they likely couldn't even start on the level.
erikem wrote:a circa 1920 Baldwin publication that shows the minimum rolling resistance for a passenger train as 4.5 lb/ton at 8 to 10 MPH. The 0 MPH intercept on the graph appears to be 15 lb/ton, 2 MPH looks to be about 10 lb/ton, 5 MPH is about 6 lb/ton.
Supposedly N&W A's took 12500 tons [unassisted] to Columbus, climbing an 0.3% grade a few miles long, and C&O 2-10-4s supposedly took 13500 tons [unassisted] on their 0.2% grades to Columbus. Think it would be hopeless for either one of them to restart if they happened to get stopped on the ruling grade? Come to think of it, if rolling resistance were 10 lb/ton at 2 mph they likely couldn't even start on the level.
Let's look at a C&O 2-10-4 trying to start its 13500-ton, 160-car train on level track, supposing the train needs 10 lb/ton = 135,000 lb to roll at a constant 2 mph on the level. Once the slack is all stretched they have to be going faster than 2 mph, or the train will refuse to accelerate (since the engine's TE of 109000 is less than 135000) and shortly grind to a halt. So we'll aim for 3 mph when the slack is all stretched-- how about we say 7 lb/ton train resistance at 3 mph?
First off we have to bunch the slack, which will be a struggle in itself, but say we manage that. We flip the Baker to full forward gear and accelerate the engine and the first few cars to 3 mph, 4.4 feet/sec. For now we'll assume a foot of slack per car-- so one after the other the cars are accelerating from 0 to 3 mph in 0.227 seconds, which requires a pull on each car of around 104,000 lb for that time just to overcome its inertia -- whatever it takes to overcome its friction is additional. Meanwhile more and more of the engine's TE is being absorbed by the already-stretched part of the train-- when we've stretched the first 120 cars they're demanding 70000 lb to maintain 3 mph. So clearly we can't maintain 3 mph. As the front of the train slows it's easier to tug the slack out of each remaining stationary car-- but supposedly the resistance of the already-rolling cars is increasing as their speed drops toward 2 mph. I'm too lazy to program the calculator to solve that problem, but wouldn't you agree it looks pretty hopeless?
So you need more slack. Any chance for 2 ft/car? I'm guessing not, but what do I know.
Additional complication: what if we haven't bunched all the slack -- the last ten cars are stretched? The 150th car, moving at, say, 2.5 mph, meets the last ten stationary-with-no-slack cars, that have to be accelerated to 2.5 mph in 0.27 seconds, requiring 700,000 lb or so...
re: "I'm also wondering how much the low speed rolling resistance of journal bearings depended on ambient conditions"
I suspect they did make a real difference. The lube would have appreciably different properties if sitting cold for a while and hitting an ambient temperature of 10 deg. F, versus sitting in the summer sun and hitting 90 deg. F, versus temperature after operating (what 150 deg. F or more?).
Q: Does anyone know whether the used different lubricants at different times of the year? Or for different train weights? I.e., would they maybe use a thinner lube on a heavier train, to give the locomotive a better chance to pull it, at the expense of increased wear?
Feltonhill wrote: "Best I understand it, the Y5/Y6's had a form of limited cutoff, with an adjustment factor averaging around 75%."
I am not 100% of what you are getting at, but I will tell you this. Just last night I was re-reading the relevant sections in the revised edition of N&W: Giant of Steam, and the report there was that the Y5/Y6 originally allowed steam admission over, IIRC, 90% of stroke in the HP cylinders and 88% in the LP cylinders, but that this extreme amount of steam admission was found to provide little extra TE, while causing the valves to work less optimally at lower cutoffs. So they rebuilt the valves, and among the changes the new maximum cutoffs were 80% and 75%.
Also, just to point out, there are so many issues and fudge factors that I don't have any confidence that anyone can come up with a precise answer to the main points being discussed here.
One of the main things I neglected to mention previously, that someone else did mention, is that usually there is some slack, so the locomotive is not really simultaneously starting the train. How you can really account for this, precisely, with all the various experimental figures being discussed is certainly beyond me.
Frankly, I think the whole system is so complicated that there's no way to answer the question today, and even in 1952 or whenever, the only reliable answer would have come with a freshly-shopped loco, a skillful engineer and fireman, and a dyno car. Other than that, we're guessing. (Not that it can't be fun to guess and discuss.)
I didn't think you were suggesting taking slack was a myth.
Assuming the train was starting on level track, the difference between the 4.5 to 5 lb/ton rolling resistance at 10 MPH and the 10 lb/ton rolling resistance at ~2MPH is equivalent to a 0.25 to 0.275% grade. If the train can't start at 10 lb/ton on level track, it certainly couldn't go up a 0.3% grade.
Doing a bit of Googling turns up a starting TE of 93,000lb plus another 15,000lb from the booster for the C&O T-1, which is probably just enough to get the train going by taking up slack (works out to be 8 lb/ton of available tractive effort for the whole train). Interestingly, the article stated that the trains usually got a helper when ascending the 0.3% ruling grade.
I'm also wondering how much the low speed rolling resistance of journal bearings depended on ambient conditions and recent (as in the last few minutes) operation.
timz wrote:Supposedly N&W A's took 12500 tons to Columbus, climbing an 0.3% grade a few miles long, and C&O 2-10-4s supposedly took 13500 tons on their 0.2% grades to Columbus. Think it would be hopeless for either one of them to restart if they happened to get stopped on the ruling grade? Come to think of it, if rolling resistance were 10 lb/ton at 2 mph they likely couldn't even start on the level.(Yeah, I know-- you're figuring they can sequentially jerk each car from 0 to 3 mph, using the slack in the train to get past the purported drag at 2 mph. I'll have to think about that a little more-- I suspect pure inertia will rule it out. How much slack do you think we should allow per car-- a foot, or two, or what?)
Supposedly N&W A's took 12500 tons to Columbus, climbing an 0.3% grade a few miles long, and C&O 2-10-4s supposedly took 13500 tons on their 0.2% grades to Columbus. Think it would be hopeless for either one of them to restart if they happened to get stopped on the ruling grade? Come to think of it, if rolling resistance were 10 lb/ton at 2 mph they likely couldn't even start on the level.
(Yeah, I know-- you're figuring they can sequentially jerk each car from 0 to 3 mph, using the slack in the train to get past the purported drag at 2 mph. I'll have to think about that a little more-- I suspect pure inertia will rule it out. How much slack do you think we should allow per car-- a foot, or two, or what?)
I've seen several references to trains crews being surprised and delighted with not having to take up slack with diesels as opposed to steamers. Being a bit too young to remember railroading in the days of steam, I can't vouch for engineers needing to take up slack before starting, but I've seen many references to the practice. I recall a couple of references to have to take a couple of iterations to get the train moving, the back and forth should ensure that oil gets in the bearings of the cars in the front of the train.
The figure that sticks in my mind is 6 inches of free slack per coupler.
Very impressive dig'in into formulas and sources here...Go ahead, please!
Lars
feltonhill wrote:The 75% adjustment factor I referred to would be substituted for the more usual 85% of Boiler Pressure in the standard TE formula.According to my estimates, and that's all they are, the as-built Y6's had valve timings that reflected an adjustment factor of about 74%.
According to my estimates, and that's all they are, the as-built Y6's had valve timings that reflected an adjustment factor of about 74%.
The 1938 Cyc gives the usual 126,838 TE for the Y6, requiring 85%. Did N&W itself assume less?
The 1930 Cyc's TE for the Y3b also requires 85%.
The 75% adjustment factor I referred to would be substituted for the more usual 85% of Boiler Pressure in the standard TE formula.
According to my estimates, and that's all they are, the as-built Y6's had valve timings that reflected an adjustment factor of about 74%. The final Y6b's and the improved Y6's were closer to 82%. This is for starting TE only and the percentages are "plug numbers" I used to adjust the TE formula to reflect N&W's test data re: TE and drawbar pull.
There were several interviews with N&W engineering personnel (Pilcher, Pond, McGavock.....) that were used background information for Jeffries' book, N&W Giant of Steam. Pilcher specifically discussed valve events and cutoffs, but no exact timing data was mentioned, IIRC. Still, we're lucky to have that kind of first-hand info. This is where I got the idea that the increases in TE/DBPull were the result of increased MEP caused by modified valve timing.
So far I don't recall seeing any specific detailed data regarding valve settings in NWHS archives material, but several of us keep looking every month!
timz wrote: erikem wrote:figure 0.3% (6lbf/ton) for journal bearings and 0.2% (4lbf/ton) for roller bearings.In 1926 Davis said loaded cars (say, 80 tons on four axles) needed around 3 lb/ton at low speeds. No reason to think he was wrong.
erikem wrote:figure 0.3% (6lbf/ton) for journal bearings and 0.2% (4lbf/ton) for roller bearings.
In 1926 Davis said loaded cars (say, 80 tons on four axles) needed around 3 lb/ton at low speeds. No reason to think he was wrong.
I'm looking at a graph from a circa 1920 Baldwin publication that shows the minimum rolling resistance for a passenger train as 4.5 lb/ton at 8 to 10 MPH. The 0 MPH intercept on the graph appears to be 15 lb/ton, 2 MPH looks to be about 10 lb/ton, 5 MPH is about 6 lb/ton. The caption stated that this graph was valid for car weights of 45 tons and higher. Even though this was intended for passenger cars, the rolling resistance for freight cars at low speeds should be about the same.
timz wrote: erikem wrote:journal bearings can be as high as 10 to 15 lbf/ton below 1-2 MPH.That seems to be a persistent legend-- that friction bearings get draggier at low speed. But if N&W 2-8+8-2s really could start 5150 tons on a 1% upgrade (or if they could start their rated 13500 tons on the 0.3% upgrade on the line to Columbus) 10 lb/ton at 0.5 mph sounds unlikely.Then again-- for all we know maybe they couldn't start their trains on the ruling grades.
erikem wrote:journal bearings can be as high as 10 to 15 lbf/ton below 1-2 MPH.
That seems to be a persistent legend-- that friction bearings get draggier at low speed. But if N&W 2-8+8-2s really could start 5150 tons on a 1% upgrade (or if they could start their rated 13500 tons on the 0.3% upgrade on the line to Columbus) 10 lb/ton at 0.5 mph sounds unlikely.
Then again-- for all we know maybe they couldn't start their trains on the ruling grades.
I would be more inclined to think that the trains could not be started on a ruling grade - you're heard of a "grade" marker on some signals - a heavy train is permitted to pass a "stop" specifically because the train may not be able to start again after stopping on the grade. This is also why engineers would take up slack before starting, they would only need to get a couple of cars started at any given instant, minimizing the number of cars at near zero (high drag) speed.
Journal bearings rely on the journal riding on a film of oil on the axle end. At low speeds, there isn't enough oil being carried in to maintain that film against the weight of the car thus increasing friction.
feltonhill wrote:I assumed they used the formula found in various text books and that differences were caused by N&W's experimentation with...
You're right-- I thought I had been thru the figures and they agreed, but they don't. The Cyc shows 101480 for a Y3b when the formula says 101465, and Jeffries says 114154 for a 270-psi engine with 58-inch drivers when the formula says 114148 with 57-inch drivers, and the X1-Y1-Z1-Z1b are off by larger margins as you're no doubt aware.
I don't remember seeing cutoffs or lap-lead figures for the Y's, either before or after the circa-1950 change. "An adjustment factor averaging around 75%" of what? That's before 1950?
timz wrote: dredmann wrote:An old rule of thumb has been reported, that a friction-bearing train needed maybe 25% more than simple frictionless calculations based on tonnage and grade would indicate, which would take you to about 129,000 lb.Best forget that rule of thumb. Like you said, 103,000 lb to overcome gravity on a 1% grade with 5150 trailing tons (plus more for the engine and tender), but the train's friction resistance won't be 26,000 lb at low speed, once the bearings have warmed up. (I'm assuming it's a 5150-ton loaded coal train. If it were 5150 tons of empties, might have to reconsider.)
dredmann wrote:An old rule of thumb has been reported, that a friction-bearing train needed maybe 25% more than simple frictionless calculations based on tonnage and grade would indicate, which would take you to about 129,000 lb.
A rule of thumb from the article on grades in an early 1968 issue of Model Railroader, figure 0.3% (6lbf/ton) for journal bearings and 0.2% (4lbf/ton) for roller bearings. The figure for roller bearings is probably vaild down to zero speed, but journal bearings can be as high as 10 to 15 lbf/ton below 1-2 MPH. The 25% increase is correct for 1% grades, but understates added friction for lesser grades and overstates for steeper grades.
(lbf = "pounds force" or simply pounds)
I looked at the chart for the eastward climb over Blue Ridge. As everyone knows the first few miles is easier, then once the grade stiffens it climbs 234 ft in (scaling off the chart) 4.04 miles, which equals 1.10% average. Curvature in that distance totals somewhere around 278 degrees of total angle; using the usual curve compensation formula (0.04% per degree of curve sharpness) that makes the average compensated grade 1.15%.
The last 1.28 miles to the west end of the vertical curve at the summit averages 1.24 or 1.25% compensated: 79 ft altitude gain, 120 degrees of curvature plus maybe a few degrees of that concave-south curve at the summit.
For their grades, at least at sherman, it seems to be UP used BB as a 120.000lbs cont. pull@15mph Machine...compared to diesels...
-EDIT-
Not that true, sorry, better 110.000lbs@15 mph. Quite similar to BigJims's posted SD70.
Timz,
You're correct, the Y5, Y6 and Y6a all had 57" drivers as built. Following WW2 they were equipped with thicker tires, which raised the driver diameter to 58". The Y6b's were built with 58" drivers, starting in 1948.
Where did you find the info regarding N&W's method of computing TE for the Y's? I've never found a specific reference at the NWHS archives, at least not yet. I only have three days a month there, and detailed computation books are few and far between. Only found three so far. Lacking any specific info, I assumed they used the formula found in various text books and that differences were caused by N&W's experimentation with valve timing on the Y's as they tried to get more "production" out of them. This would cause variations in the MEP. Best I understand it, the Y5/Y6's had a form of limited cutoff, with an adjustment factor averaging around 75%. If you found a reference I can guarantee that at least two people here (Big Jim and me) would be very interested in getting a copy of it to the NWHS archives. Although a lot of information on N&W locomotives has survived, this is one area where there is less than I would like to see.
If you prefer to contact me off line, my e-mail is still the same.
So much thank you, BigJim!
hope nobody got bothered with this thread, fine it's still alive . Any other figures (this should no become a Black vs. White thread, please) for other specific combinations are welcome!
Maybe, the aim to compare engines just by their drawbar or tonnage pull at certain speeds is not as exact as I thought first. There seems to be many more factors than just engine related ones: achieved speeds, range of fuel or moving tonnage just beyond stall weight.
What do you think about the achieved average 3500hp and 70000lbs TE effort on the BB test runs (Kratville, P. 23)?
If we compare some diesel classes on specific runs, can we draw trends for steamengines? I tried to do this here: http://www.trains.com/trccs/forums/1268000/ShowPost.aspx
Excitingly waiting for your charts...
Question is, how much of Blue Ridge was 1.2% and not 1.1%?
Can we draw following conclusion: at a ruling grade of ~1% ratings for Y6 was 5200tons and at ~1.2% it was 4600tons ?
re: "So what TE would it take to start a 5150-ton train that happened to get stopped on the 1%? We don't have much idea-- nobody knows exactly how much TE it took to start a friction-bearing train."
That's very true. But we can say that some theoretical frictionless train of 5150 tons (assuming 2000 lb tons, not long tons or metric tons) will require a constant force of about 103,000 lb to pull up a 1% grade. An old rule of thumb has been reported, that a friction-bearing train needed maybe 25% more than simple frictionless calculations based on tonnage and grade would indicate, which would take you to about 129,000 lb. Also, with friction, the starting force will have to be somewhat higher than the rolling force, so yes, starting the train is the hardest part. I will readily grant you that old rules of thumb have questionable accuracy and less-than-stellar precision! But, well, that's probably about as good an idea as we're going to get, Monday-morning-quarterbacking N&W operations of fifty years ago.
By the way, it is my understanding that all or virtually all of the Y5 & Y6 class locomotives got new tires that were 0.5-inch thicker, which then increased the outside diameter of the wheel-and-tire set from 57 inches to 58 inches.
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