Ruling Gradients

[Sub MandrelParticipant @submandrel]

What is typical?

[Sub MandrelParticipant @submandrel]

I understand that the steepest gradient on a railway track is known as the 'ruling gradient'.

My shunter struggled at the Derby SMEE track, stalling at the very steepest two points. Their steepest gradient is 1:75, although I suspect that the very short sections that got me were perhaps even steeper as I was able to make gentle progress up most of the 1:75.

Could anyone give examples of the 'ruling gradients' on other tracks?

Thanks

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Neil ,

Ruling gradient is defined as that maximum gradientup which a locomotive can take a maximum load appropriate to its class without assistance .

Note that this ruling gradient is meant to be one over which normal trains can be run as regular activity and it is not the stall gradient which is a good bit steeper .

Not actually a very meaningful term because effect of gradient is altered considerably by length of gradient , curvature and whether it is a one off gradient or part of a compex varying gradient profile .

Rules varied a lot from railway to railway but most considered that there was a break point at about 1 in 100 for a sustained gradient on straight track .

Anything flatter was not too troublesome but anything steeper had to be taken into account when selecting engines and train weights and possible need for double heading or banking engines .

A simple bit of trig will equate the engines TE to gradient and train weight ( including a small allowance for friction ) so stall , hard work and easy running cases can be estimated quite easily . In practice though it as all done with trial and error and many years of running trains .

5029 came up a 1 in 80 with excursion set today without any difficulty .

On model steam running lines the same break point gradient seems to work as full size .

And Neil – where we come from the railways mostly regarded anything up to 1 in 60 as practically flat .

Many years ago I had just one run in a steam hauled passenger train up Abercynon bank – and that would frighten a designer of fairground rides . Perfect driving of a BR class 4 took us up there but the engine beats were like cannon shots . Memorable .

PS: There are ruling down grades as well . There were just a few places around here where ability to brake and control trains going downgrade was critical .

Regards ,

MikeW

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

The term Ruling Gradient is often used in a slightly less correct but more intuitively understandable way to describe a specific location and gradient which effectively define the maximum weight train that can be run on the entire line with normally available engines .

Ruling gradient in this usage is not nescessarily the steepest gradient – just the most difficult for running trains . For instance a short severe gradient may or may not be more limiting than a long less severe one .

Sections of track with sever gradients are often named – for instance Cocket Bank and Lickey Incline .

The steepest gradients in UK to be regularly loco worked were on the Cromford and High Peak line with some sections climbing at between 1 in 12 and 1 in 14 .

I used to read in Ian Allen annuals of long ago about groups of intrepid railway enthusiasts paying a nominal fee and signing an indemnity before being given a spectacular ride up the inclines in open mineral wagons .

MikeW

[Sub MandrelParticipant @submandrel]

Thanks for putting me on the level

Has anyone got any specific examples of the maximum gradients on some club tracks?

Is 1:75 usual or would 1:100 be more typical?

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Very hard to give a definitive answer about maximum gradients on club tracks .

A selection of tracks that I have visited and sometimes run on mostly seem to have no long gradients steeper than about 1 in 80 .

Most of the best tracks are more level than that with gradients between 1 in 100 and 1 in 200 .

Some tracks though of nescessity have steeper sections but usually these are kept as short as possible .

As regards actually running – anything steeper than about 1 in 100 will be a hard struggle for little engines like Tich , Juliet and RobRoy .

Your little electric diesel can have gear ratios adjusted to give more tractive effort for hill climbing if needs be but it may have to have extra weight as well if you intend regular running on steeper tracks .

Regards ,

MikeW

[Sub MandrelParticipant @submandrel]

Hi Mike,

If I drop the gear ratios, it will become raher slow on the level, and as you say adhesion is as much of an issue as power. If 1:80 is a usual steepest gradient, I won't have qualms about promoting the design, as it only seems to be the very steepest bits of 1:75 that stopped it.

Thanks

Neil

[Ian S CParticipant @iansc]

Neil, theres a project for you, a two speed drive, may not be too difficult. Ian S C

[Sub MandrelParticipant @submandrel]

I foresaw the possibility fo lacking power, so I designed the gearbox so that to fit a lower ratio, all I need is to cut one larger gear to replace an existing one. The motor can keep the same pinion, and moves upwards in its mounting slots to accomodate the new gear. To get an even lower ration, the pinion could be made smaller.

For a line that is less steep, the ratio appears near ideal. Here's my theory of the minimum drawbar pull needed by small locos:

On the level, with a ball bearing driving car, you probably need just over a pound of drawbar pull to keep moving, and no more than three pounds to get started.

The total drawbar pull needed from a small loco is therefore three pounds plus whatever is needed to pull the driver and truck up the steepest gradient.

I weigh 'about' 180lbs, driving trucks are heavier than I expected, lets say 70 lbs for a big one, so 250lbs total.

For different gradients the 'extra' pull required is:

1:100 … 2.5lbs

1:80 … 3.1 lbs

1:75 … 3.3lbs

My shunter weighs in at 26lbs, giving a drawbar pull at 25% AUW of 6.5lbs. Stall current for the motor is 7A and (with a 60% efficient drive train) at 6.5lbs pull the theoretical current requirement is 6.4 Amps.

In other words, I should have been able to predict that I would just manage a 1:75 gradient, but grind to a halt if there were any bits that were just a little steeper!

So three solutions:

1. Stick to less steep tracks (it seems most are)
2. Make my own, lighter driving truck
3. Reduce the drive gear ratio by about 20% (and perhaps add some more adhesive weight)

A fourth, rather sneaky, option is supplementary drive in the driving truck; I have already thought of a way to make this proportional to drawbar pull to avoid overdriving the loco. Whilst not strictly cricket, this would make even th steepest of tracks an easy proposition.

Neil

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Neil ,

On the completely bonkers Burry Port and Gwendraith Valley Railway the gradients were so steep and the curves so tight that no big engines could get up there . Tiny tank engines were therefore used for all purposes .( Apart from one extraordinary experiment with an articulated engine .)

Anyway modus operandi was to couple up as many tiny tank engines as were available and double or triple head on the quite heavy mineral trains .

This tradition continued from earliest days to the closure of the line with tiny diesels taking over for the last few years .

The Cornish Mineral Railways did something similar with little saddle tanks coupled back to back and with open back cabs so that one intrepid (and energetic) crew could work both engines .

There’s your answer – build your engines in multiple and couple as many together as are needed for running on troublesome tracks !

Regards ,

MikeW

Edited By MICHAEL WILLIAMS on 19/09/2013 09:58:24

Edited By MICHAEL WILLIAMS on 19/09/2013 10:00:28

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

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[Sub MandrelParticipant @submandrel]

That looks pretty steep Michael. I think I prefer ===

Neil

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