Push pull trains

rrman posted:

Watched a video where a passenger train was bookended by two ex-Amtrak same type/style engines.  Made me wonder if the consist is easier to control with a off line "dead weight" rear engine tagging along keeping things stretched,

First, how do you know that that rear engine is "dead"? Some of Amtrak's trains do indeed have powered units at each end.

or if the rear engine causes problems when braking and bunching?

No, no problems since everything is electric train-lined braking. Also, Amtrak has many operations in the Pacific Northwest, where the unit on one end is actually just a dummy (called a 'Cabbage') with nothing inside except a baggage compartment (thus the name 'Cabbage', for 'cab controls'  and  'Baggage')

Or no problem and reacts just like another car?

Right.

A lot of times Amtrak and possibly some commuter rail will bracket a consist of passenger cars with a locomotive on one end and a cab control car ( that looks like a loco but has been demotored) on the other for end protection for the passengers on board. The L.I.R.R. did this from the 1960's to the 1990's on their dieselized trains. 

I thought the LIRR had some MP15 switchers which could run either as a locomotice or HEP cab unit, but not both at the same time.

New Jersey Transit using push-pull operations shown here at Little Silver, NJ on the shuttle service during the extension of the electrification to Matawan in 1982.

Excuse the quality of the photograph.  I was 13 when I took it with my 35mm camera that was all plastic.  The was an E8 on either end and three coaches between. 

Some LIRR equipment- This was the Greenport Scoot

As followup, I was watching a DVD from Yardgoat Images showing the NRHS excursion trips in Cedar Rapids Iowa.  The consist was a mix of private coaches book ended by a pair of Iowa Northern Railway that were identical (at least exterior wise) ex-Amtrak engines.  Cannot say if the reverse running unit was off-line or assisting, as the terrain for the most part was flat, so one unit should be able to pull the load.

RSJB18 posted:

Some LIRR equipment- This was the Greenport Scoot

That looked like the passenger set K-Line soldin the 1990's.

645 posted:

I believe most all modern passenger equipment these days are equipped with tightlock couplers so there is little slack action compared to traditional couplers. In other words the entire consist moves as one piece. Can get away with it compared to a long freight since a passenger consist is usually short - no need to start out "car by car" as it were. I'm sure others who actually run passenger/have experience will chime in on this to confirm this or correct me if I'm off base here.

Pretty much as you imagine it, but not completely free of slack.  Skill and finesse control slack.

Most lightweight passenger cars were indeed equipped with tightlock couplers, which were designed to do two things:  1. Prevent cars from uncoupling in a train derailment; and  2. limit harsh slack by using some spring tension between couplers.  They were an improvement in both areas, over standard couplers, but nowhere near flawless in either respect.  For some reason, not all railroads used tightlock couplers on their lightweight head-end cars, and Amtrak wound up with a few of those in its fleet.  I worked Amtrak trains as an Engineer on the Los Angeles Division of Santa Fe between 1980 and 1984, and recall that the Southwest Chief often had these baggage cars.  When bunching or stretching the train, it was critical to feel for that baggage car and make sure to be extra gentle with it.

The best cars for train handling, in my opinion, were the Amfleet cars.  They had very little slack, and good braking response, and they worked very well with F40PH's using blended dynamic braking, when in a solid train of Amfleets (as the San Diegans were then).  With mixed types of cars, it's best to manually control dynamic braking, no matter what kind of couplers are on the cars.  Amtrak's Superliner cars and the ex-Santa Fe Hi-Levels also had pretty good handling characteristics, but these were heavy cars that required setting more air, and had to be handled accordingly.  The Hi-Levels and the Superliners were not identical in their handling characteristics.  On the Southwest Chief, then, there were two baggage cars -- sometimes without tightlock couplers -- a block of mixed Superliners and Hi-Levels, and sometimes sleeping cars behind them.  Train handling was certainly not brainless, but was easier than freight service, because the train was shorter (and thus more responsive), and graduated release could be used.  On freight cars, when the brakes release, they completely release.  On passenger cars, the brakes can be released a bit at a time, in several increments, which allows better control of slack, smoother release at speed, and enables smooth stops.

So, yes, tightlock couplers do help to control slack, but they do not make the train start without slack, unless it has been stopped with the slack completely stretched.  That's why good passenger Engineers do not release the brakes and allow slack to adjust before applying power.  The best technique is to stop with the slack all stretched (head end locomotive) or bunched (rear end locomotive) and then start by applying power first and then graduating the brakes off.  When changing directions, you can use graduated release to help change the slack from stretched to bunched, or vice-versa, but you have to be patient and use a lot of finesse.  Exceptional passenger train handling requires a few extra seconds for every braking event.  With commuter trains it is less important than with trains having sleeping and dining cars.  Commuters will tolerate brick wall stops from Alley-Oop Engineers, but that's how a lot of commuter cars get flat spots on their wheels.  Smooth commuter stops are preferable.

As for powered units at each end of the train, I rode the Vermonter in 2008, with live locomotives fore and aft, and the train handling was quite smooth, so it can definitely be done well.  I would bet, however, that a poor Engineer could make the front and rear locomotives play the train like a concertina.