Hi All

A friend is working with the grade profile sheets from the SP for the Cloudcroft branch. The ruling grade listed is 6% but the rise over run calculates to a lower percentage. The railroad when built railroad was built with spiral curves based upon Searles writings. The curvature was 30 degrees. The line was in a near constant curve. How did the SP determine ruling grades? Did the SP determine the ruling grades by both the rise and the curve resistance or by other factors? Thanks for the help.

Robby

The 'ruling grade' is the maximum resistance experienced on a particular track section. As you note, it can be a combination of grade and curve resistance, and in my experience is defined as effective starting resistance (i.e., no allowance for 'momentum grade').

The 'compensation' you described in the thread title is a bit different; it consists of reducing the physical grade at the 'peak' resistance points in curves, most particularly in areas that would establish the 'ruling grade' if the compensation were not done. Where transition spirals are used (cf. Klauder for a modern reference, where both horizontal and vertical spiraling is discussed) the effective 'grade' on the inner and outer rails is slightly different, and the (rise/run) at the peak points of effective resistance in the curve would be adjusted for the compensation.

I am sure that someone from CSRM will know the exact procedures used by SP and will provide them, or a link to them.

Hi,

I wrote a book "Civil Engineering for Outdoor Railroads" which is basically a "For Dummies ..." type book. It is published by Authorhouse.

The book was targeted to the Live Steam hobby. However, the basics come from full size work.

There are some 10-odd pages (out of 191) concerning grades and compensation.

If you are interested in purchasing the book or seeing some sample pages, please let me know.

Basically there are three main types of resistance to moving a train. 1) Rolling resistance, 2) grade resistance, and 3) curvature resistance. One the resistance to movement is known, the same resistance can be backed out into an equivalent grade or equivalent curve. This is how the grade can be reduced to keep a constant resistance with a lower grade plus a curve. This is a compensated grade.

I hope this helps out.

Doug vV

I am not sure how far train-factor concerns affect formal designation of ruling grade per se. It was my understanding that calculation of the ruling-grade factors was made and then used as one of the elements in calculating train length or consist make-up, rather than the 'rolling resistance' elements being lumped in with the fixed civil.

In my opinion, I am vaguely disturbed when I read commercial 'pitches' or plugs -- be they for ever so useful products -- on the Interchange directly. This is just as true for how-to books as for patent boiler treatments or tribological packages. In this case, the information Robby requested is something that can easily be provided 'free' and I think should continue to be provided strictly on that basis - he can, of course, PM Mr. van Veelen to arrange for a copy (and I am in great sympathy with Mr. van Veelen's getting income from selling copies).

Veelen. It's a good basic book for anybody who needs to build or rebuild track in any scale and isn't an engineer. No, I don't own a piece of it.

Hi,

I did not intend for it to be a commercial plug. I checked my post and I did not get the idea out that if someone wanted the 10 pages, they could contact me and I'd send them to them. If there was more of interest in the book for them, then I was not prepared to give away books free.

I am currently having health problems and am a step away from being homeless.

Sorry about the confusion.

Doug van Veelen

While it may be too early an example for you, and it only tells what was done, not how they calculated it: George Vose wrote in his 1872 classic Manual for Railroad Engineers that the Central Pacific "flattened" the grade upon curves from 2 to 2-1/2 feet per mile per degree of curvature--i.e. the grade upon a ten degree curve would be reduced from 20 to 25 feet per mile. The CP did not introduce spirals until about 1876. It would be interesting to know how they dealt with the transition of grades as alignment moved from tangent to curve.

Incidentally, ten degrees was the sharpest curve on the Central Pacific as completed (one 14 degree curve in the Palisade Canyon was soon eased by realigning the Humboldt River). Many of those ten degree curves in the Sierra remain--and one is actually a bit tighter due to the introduction of spirals.

While compensating the grade worked well in getting a train up the hill, I imagine it made braking a real pain on the downhill, where resistance would increase going around "flattened" curves, and then drop off on the steep tangents.

Hi,

That quote is not from me - (Douglas vV - Douglas van Veelen).

BUT the point is very well made. You just need to know the territory (like in the Misic Man <GRIN>).

Doug vV

Even 25 feet per mile is only 0.4 percent. Using BNSF's industry lead standards (the quickest thing I could find) you multiply that by 100, so the transition is only 40 feet long and rather subtle. Personally, I'd probably just split the difference, half in the curve, half in tangent. We're only talking 20 feet on either side, won't matter much. Even if they didn't use actual spirals, there tends to be a bit of natural spiral as you enter the curve due to the rail's rigidity.

Holy cow! Sounds like a geared locomotive playground, but I don't recall SP being known as a fan of geared locos.

Bob, I think this is the Alamogordo & Sacramento Mountain (which only came under SP lease in 1924 or so).

Interesting motive power history. They had a couple of big Shays as expected power ... which were too heavy for the construction and sold off quickly. Lots and lots of logging company Shays ran over it.

Some interesting coverage here: http://www.foresthistory.org/ASPNET/Publications/region/3/lincoln/cultres4/contents.htm

Hi All,

THE SP did take over the branch in 1924. The way the official grade between the railroads differed That raised the question. The branch saw two attempts to operate shays on the line but length of the run vs fuel tank size and other operational challenges along the line created issues. Even 40 foot cars and the amount of coupler swing was an issue at various times for the RR. Here below is some thoughts on the line I received .



Robby,
Here is the one item I found earlier that related compensation to actual operating conditions. Where it is not practical to reduce the grade, as in the mountain canyons of the approaches to Cloudcroft, then the ruling grade or effective grade needs to be increased. The compensation of 0.03 percent or 0.04 percent per degree of curvature takes you from the actual 5-plus percent to the SP's stated 333 feet per mile or 6.31 percent ruling grade. Here is Tratman's text:

Tratman, Railway Track & Track Work
Third Edition, 1909, McGraw-Hill
p. 386
Compensation of Grades for Curvature

"When curves occur on heavy grades the grade should be so reduced that the combined train resistance due to grade and curve will not exceed that due to the maximum grade allowed on the tangent. This reduction is variously taken at 0.03 to 0.05 per degree. Thus with a maximum grade of 2 [percent] on tangents and a rate of compensation of 0.04 per degree, the maximum grade on a curve of 6 would be 1.76 The amount of elevation lost by compensating the grade is found by multiplying the degree of central angle of the curve by the rate of compensation and this elevation divided by the length of grade will give the rate by which the tangent maximum must lie increased to introduce the compensation without a final loss in elevation The change in grade may commence at the nearest even station and not necessarily at the PC or PT The reduced grade usually extends beyond the curve To avoid too great a loss in elevation or too heavy a grade on the tangent it may be necessary to modify the rate of compensation, but this will depend largely upon traffic conditions The compensation should in general be introduced even upon easy grades especially those which approach the rate of ruling grade in order to provide for future increase in train loads or reductions in grades For curves of 10 or over the rate of compensation may be reduced A rule in general use at one time required an increase in compensation on sharp grades but Wellington's Economic Theory of Railway Location which gives perhaps the best exposition of this subject shows that this was based upon the erroneous assumption that curve resistance increases with the degree of curve On a curve immediately above a regular stopping place the compensation may be 0.10 to allow for trains that have not acquired speed On a curve immediately below a stopping place the rate may be reduced to about 0.03 but in Prof Webb's Railway Construction it is stated that no compensation need be used under such conditions as the resistance due to the curve will correspondingly reduce the work required from the brakes in stopping a train Engineering News April 23 and June 11 1908 There is a great diversity of practice which is based largely upon opinion and experience and there is much need for careful experiments in order to give some definite knowledge as to the requirements under modern conditions of rolling stock and traffic On the Northern Pacific Ry a compensation of 0.03 was found insufficient 0.04 gave fairly good results but was not quite sufficient with curvature frequently changing in direction while on very long curves in one direction the rate was somewhat in excess of requirements This was noticeable only on long trains and the condition of the cars had a good deal of influence upon it The Illinois Central Ry has adopted 0.04 and increases this 0.1 at stopping places On its Indianapolis Southern line 0.04 was used when the length of curve was equal to that of the maximum train and 0.03 when its length was not more than half that of the maximum train On the Louisville & Nashville Ry 0.03 has been found insufficient where a great many curves occur close together and in future the compensation will be 0.05 In compensating at stopping places the practice is to reduce the grade 0.2 in addition to the compensation for curvature On the Chicago Milwaukee & St Paul Ry compensation for curvature on maximum grades is generally at the rate of 0.035 In some cases this is reduced to 0.03 It is not the practice to compensate for curvature near stopping places but if such stops are on maximum grades the grade is reduced 0.1 to 0.2 On the Philadelphia & Reading Ry the compensation is 0.04 per degree and this applies also to stopping places On the Canadian Pacific Ry the compensation is 0.04 on ordinary work but in tunnels this is increased to 0.06 on account of the probability of damp rails."

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Robby Peartree