As a freight train goes around a curve, is the stability effected by the number of boxcars? If a train...?

Question

is significantly longer than normal, would the tail end be more likely to tip over? My husband and I are, um, debating this. I've said that it would be more likely to tip - and used the example of a semi truck pulling a fully loaded container going around a corner. Assuming that your driver is professional and able to adjust the speed, etc. and assuming that the engine has enough power... now imagine the truck pulling 2 containers (Super B) . ok, can be done. Now imagine the truck pulling 8 containers! Those last few containers are much more likely to tip, aren't they? My Husband almost agreed with me for a moment there but says it's different for trains because they run on tracks, so it makes no difference if the train has 100 cars or 200. (sigh - I even tried a little kitchen experiment with cans of pop but the elastics kept breaking) Does anyone know the right answer here? We have a back rub riding on this! Thanks!

Answer 1

Absolutely.  Number of cars has a huge impact as it relates to overall length and, most importantly, tonnage.  But you won't find problems near the rear end of a train when length and tonnbage become extreme.  

The key is a thing called "L/V."  It is the ratio between vertical force (gravity) and the lateral force (centrifugal and centripetal) found when traversing the curve.  As long as the lateral force stays low in relation, the equipment will stay atop the rail.  But, if "L" becomes .9 of "V" or greater, you are going to have a derailment.

If traversing a curve in draft (pulling the train) and the lateral force becomes to high, the equipment will be pulled off the inside of the cyrve.  This is what caused the infamous "Cantara Loop Disaster" in 1991.

Here is an experiment you can easily do to demonstrate.  Get a few pienes of curved HO Scale model railroad track, and put them together.  Now, cut a length of ordinary string long enough the hang out the end ends of the track, and lay it between the rails.

Now, pull on one end, not upward, but long wise.  You'll see the string stay between the rails.  Now, repeat the experiment, but place a finger on one end of the string as you pull.  What happens?  You'll see the string straighten out and go outside the rails.  This is called "string lining" and the same will happen to a train long enough or heavy enough to generate excessive draft levels.

Conversely, if the train is operating with the engines in dynamic brake and the forces become excessive in "buff," with the tonnage against the engine, and L/V is exceeded, then the cars near the head end will be "punched" out the outside of the curve.

In most instances, helper engines are employed either behind or within the train so that leangth and tonnage is manageable without creating the excessive forces.

The kind of "whiplash" effect you're describing in your question does occur, but due to the amount of "slack" in the train.  Obviously, the more cars, the longer the train, the more slack there is.  The engineer not only controls the speed of the train, but management of the slack is a major concern as well.  Excessive slack action can damage lading or cause a derailment.

A very good question.  Thanks for asking.

Addendum:  I put this answer in, in chunks this time around... and as anyone who knows me will tell you, I over-do everything... LOL.

Answer 2

Yes

and

No

I was going to pass on this one, but I'll throw in my 2 cents worth, it is an interesting question.

On a long train, the first few cars are the most likely to derail because of the in-train forces described above.

The whiplash effect you are asking about does not affect the rear car any differently than the head car.

Seems odd if you have ever played "crack the whip" while ice skating but all cars in a train are taking the same course, and traveling the same distance around the curve so all are going exactly the same speed and have exactly the same centrifugal force acting on them.

Semi trucks dont have rails holding the wheels to a specific course and can get to "whipping" in a curve so that scenario is not necessarily applicable. Your kitchen experiment wouldnt have worked for the same reason, no rails.

Thanx for asking, I had to scratch my head a bit.

If I were you, I would get the back-rub oils ready.

Answer 3

Get ready to do the rubbing. It makes no difference how long the train is.A train has something called a node point.When you pull on a train the node travels the length of the train and equalizes the pulling force.Think of it like a ripple in a swimming pool.It starts at one end and travels to the other end.The only danger to making cars tip over is something we call string-lining.That can happen at low speed when too much horsepower is applied.What can happen is you develop so much pulling force that the cars on a curve are pulled off the track by the natural forces trying to pull them into a straight line.I hope your hubby enjoys that back rub!