Prototype Railroading: Helpers and Grades

The idea of helper locomotives is about as old as mountain railroading.  Anytime a heavy train needs to go up a steep or long grade, additional locomotives are needed, called helpers.  Modern diesel locomotives have not eliminated the need for helper locomotives.  They are used in many places throughout the mountains states where there are significant grades.  In most cases, helper locomotives are found on the rear end of the train, pushing, although they can be used at the head end, or in the middle.  This is less common, simply because it presents more complicated switching to get them there and to take them out later.

Glendive is actually a helper base, for trains heading east.  As trains head east from Glendive, into North Dakota, they must go up two hills.  The grades are not what many people would consider particularly steep.  Beaver Hill, the first grade encountered by eastbound trains is a 1.11% grade, and Fryburg Hill, the second one, is a 1.06% grade.  One percent really does not sound like a steep grade, but what must also be considered is the tonnage of the train and the amount of horsepower.

Typically, coal trains around here will run with two locomotives on the head end, and one distributed power unit on the rear.  Usually that means the total horsepower is around 12,000  One of these coal trains typically weighs between 16,000 and 17,000 tons, meaning there is less than one horsepower per ton.  (0.7 horsepower per ton is pretty typical.)  Another thing to consider is something called the factor of adhesion.  We are not going to get into the calculations for that, because that is rather complicated.  The factor of adhesion is basically the amount of traction a locomotive can expect when pulling a number of tons.  Typically, heavier locomotives have a higher factor of adhesion.  There is more weight on the driving wheels, and therefore more traction.  However, even the "stickiest" locomotives will spin the wheels when the load behind them is extremely high and too much horsepower is directed to the wheels.  On older locomotives, the engineer would control wheelslip with the throttle.  On newer locomotives, it is partly, or entirely controlled electronically.  There are a couple of ways to increase the factor of adhesion.  One way is to put more powered axles under a locomotive, thereby spreading out the horsepower, and transferring more of it to the rails before they begin to slip.  Another way to increase the factor of adhesion is by increasing the weight on the wheels.  This is only practical up to a certain point, because if a locomotive is built too heavy, it will overload bridges and break rails.  The simplest way to increase the factor of adhesion is to apply sand to the rails.  This will prevent wheelslip, but if a train is underpowered on a grade, it will not prevent the locomotives from stalling.  If you want more detailed information and calculations, I highly recommend visiting this website, put together by a locomotive engineer in Wyoming.

Once the factor of adhesion and horsepower per ton is figured out, then the train crew, and the railroad, can figure out what kind of power will be needed to get a train up a grade.  That is where helpers come into the equation.  On reasonably level track, most of our heaviest coal trains will do just fine with three locomotives.  Even two locomotives will get the job done, as I have talked about in the past.  On level track, the only thing the locomotives have to do is move the weight of the train forward.  Just about any number of locomotives can do that, it is just a question of how long it will take them to get going.  When a hill comes into the picture, the locomotives must not only move the weight of the train forward, but they must also move it up.  Even in short grades, this is not a problem, because on a long coal train, the train will remain in balance.  Part of the train will be ascending a short grade, while part of the train is descending a similar grade, balancing the train out.  Long grades are places where the entire train must be moving uphill at once, and there is no balancing action from a portion moving downhill.

Helper locomotives typically push on the rear end of the train, for several reasons.  It makes the switching easier when they are put on the train and taken off the train.  Also, the helpers do not usually stay with the train to the next terminal, unless that terminal happens to be the end of the grade.  This is the case in Glendive.  Once the helpers are removed from the train, they must return to the starting point.  Having them on the rear of the train makes this significantly easier.  Another thing to consider, on a grade especially, is the force on the couplers.  Typically, couplers are rated for 390,000 pounds of force.  On a grade, the force will be greater on the couplers.  Having all the locomotives at the front of the train could literally pull the train apart, breaking a coupler.  By having helpers and distributed power at the rear, it helps to prevent pulling the couplers apart.  Recently, there was not a proper balance of horsepower like that, and the train actually split in three.  When the first coupler broke, it caused such a violent change in the coupler slack that another coupler was pulled apart too.  As you can imagine, splitting a train in two is not an ideal situation.

Distributed power is different from helpers.  Distributed power locomotives, while often found at the rear end of trains, are not the same as helper locomotives.  They stay with the train for the entire trip, regardless of grades along the way.  Distributed power is a remote controlled locomotive, which the engineer at the front of the train controls, just as he would if it were up front.  A helper locomotive is attached for the sole purpose of providing extra horsepower up a long or steep grade.  It is not controlled by the engineer on the front of the train.  There is a separate crew in the helper locomotive, controlling that locomotive.  That crew and the crew on the front of the train stay in contact with each other, but the engineer on the head end of the train does not control the helper locomotive.  When the train is up the grade, the helper is removed, and the train continues on without it.

Here in Glendive, the helpers are primarily added to eastbound coal loads.  These are usually the heaviest trains we get, and they need the extra power for the hills.  The number of helpers depends entirely on the weight of the train and the number of locomotives currently assigned to it. In most cases, the coal trains will get just one helper.  They will push the train typically to Fryburg, ND, about 100 miles east, where the train will stop and the helper will be uncoupled.  The coal train will continue east, and the helper locomotive will return to Glendive.  Going up the hill with the coal train is still a slow process.  At times, with all the engines running in full throttle, the train will only be going about 15 mph.  However, that helper locomotive is the difference between keeping the train moving and stalling on the hill.  Moving slow is still better than a stalled train.  Working the helpers is usually a pretty simple job.  The first half of the trip consists of riding backwards, in full throttle, pushing the train.  As we leave town, the helper engineer puts the throttle all the way up to notch eight, the highest, and then we all sit back and watch the tracks go by.  Once at the top of the hill, it is the conductor's duty to close the angle cocks, or valves, on the air brake pipe, and pull the pin that opens the coupler.  Once that is done, the helper heads back to Glendive.  With just a locomotive, the trip back is pretty quick and easy.