COUPLER FORCES AND RUNNING TRAINS

[jsmvmd]

Dear Friends,

Hours and days of watching freight trains roll through Altoona on the flats, curves and Horseshoe Curve with 1.75% incline and ~100 foot vertical rise have led me to ask a few questions:

1. How do the lead engine and pusher engines have to work to avoid derailment?  Especially on hills and curves?

2. Why doesn't an empty flat car in the middle or near the end of a heavy consist derail with pusher engines attached?

3. How are empty cars placed in a consist to avoid derailment?  Does it matter?

I would imagine weight, length, condition of the cars, and trackage all contribute.  I have on CD a Santa Fe demo that shows oscillations of trucks at speed and how certain derailments occurred at 50-60mph, thus necessitating speed restrictions in the 1960's.

Some links I found:

http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel3%2F1152%2F1871%2F00051901.pdf&authDecision=-203

http://www.fra.dot.gov/us/content/1226

Any thoughts and comments are much appreciated and thank you in advance!

Best Wishes,

Jack

[jward]

answers to your questions:

1. outside of a few restrictions, the railroad doesn't worry much about derailments on the mountain. trains will often have 2 unit helpers on both the front and rear. you can't have too many locomotives running on the head end, if you have more than the allowed amount the rest muct be isolated. on the rear, trains are restricted to 24 axles on the helper. that works out to 2 2 unit helpers, or 4 units total.

2. empty cars can and do occasionally derail, especially the articulated ones. there are rules regarding their placement in train. any train with an articulated car too close to the rear end must have a helper ahead. a similar situation existed back when cabooses and 89' flatcars were standard on the tv trains. penn central and conrail would often place a 50' boxcar ahead of the caboose to avoid a derailment caused by pushing on a very short, lightweight car (caboose) against a car at least twice its length.

3. see #2 above.

other things railroads take into consideration are whether the locomotives are "high adhesion" which includes just about everything built since the early 1980s. in the rulebook a 6 axle high adhesion locomotive is considered as having 8 or 9 axles, both for traction, and in dynamic braking as well.

also some cars were notorious for rocking at certain speeds. rib side grain hoppers were among the examples. trains with these cars were instructed to avoid the speed range where rocking was most severe, and tonnage and motive power was adjusted to ensure they would be able to avoid that speed range.

mostly, empty cars are heavy enough that their placement in train isn't a concern.

[glennk28]

Most railroads have a list of special instructions relative to placement of cars in a train, and placement of helpers.  I recall a very good clinic given by SP Dispatcher Rick Kang at an NMRA Convention. 

As to cars rocking--this can really get severe--a former Santa Fe conductor told me of a trip in which the train "dynamited" the air--when they walked the train they found   where the train had apparently broken in tow.  So they coupled up and proceeded.  On arrival at the yard, the yard clerk informed him that they were missing a car.  So they took a motor car out to where they had made the emergency stop.  It was a track along a canyon wall.Down in the bottor was a covered hopper--it had rocked wnough to flip sideways out of the train--of course--this was why the air dynamited.  As far as I know that car is still there.  gj

[Yampa Bob]

For an experiment, I hooked up 10 old cars to a locomotive, put the loco in reverse but blocked the last car from movement. Several cars jack-knifed and derailed.

Fortunately all my couplers are metal Kadee, so no damage to the cars or couplers.

I just measured the shank length on a Kadee 148 coupler, 3/8 inch from the pivot to the knuckle center.  That equates to 33 inches for a real train. Real trains are very close coupled and don't run on such tight curves as our models. 

[jward]

as a point of clarification, the real railroad operations i described using helpers pertains to the former pennsy/pc/conrail line around horseshoe curve. it is also current ns practice there. other railroads can and do run things a bit differently. other railroads oftewn cut their helpers in the middle of the train, i can count the times i've seen this done out of altoona on one hand. also, on some lines, remote controlled helpers are used. once again, this isn't something you'd see out of altoona, where all helpers have both engineer and conductor. some other roads will use anything laying around the yard for a helper, out of altoona there has always been a small group of dedicated locomotives used for helpers (currently mostly paired sd40-2s) with occasional appearances by locomotives out of juniata shop undergoing a break in run.

[jsmvmd]

Roger that, Jeff.

The Altoona helpers are numbered in the 3000 to 4000 range if I remember correctly.  One had a pretty blonde gal at one time!

Thanks to all for the info!

Best Wishes,

Jack

[jward]

currently, they are using a bunch of former conrail sd40-2s scattered around the 3300 and 3400 series. which are being supplemented by the new sd50 rebuilds in the 6300s. eventually, ns plans to replace the sd40-2s with the rebuilds. but for now, 3335 up to about 3359 plus several other 3300s are the ones being used. 6300s are so far 6300 to 6309, and 6312, 6313. not all are in helper service.

during conrail, sd45-2s ruled the mountain for many years....