Trailer Cars

[Christopher J]

With such Trains as the R Stock, which were motored on all cars, what is the point for Trailer Cars?

Surely they just add more stress to the motors on motored cars? I've never figured out why all Cars on a Train are motored like the R stock were - especially as the R stock were very fast because of this, and speed is very important to the running of a reliable Train service.

The only Train I'm aware of which is motored on all cars at the present is the 1992 stock.

Discuss...

[Chris M]

I presume that it has something to do with maintenance costs.
I remember reading somewhere that the rule of thumb on the mainline in BR days was that over 5? carriages and it was better to use a loco and carrages rather than D/EMUs.
My guess with the underground situation is that it is cheaper and/or easier to maintain one more powerful motor than two less powerful ones.

Chris

[towerman]

Not so much these days,but in days of yore esp on tube stock,with motors, MA's and stuff there was no room for the compressors.So if we have a car with nothing else on it,hey presto we have somewhere to put the compressors.

[q8]

This is all swings and roundabouts really. An all-motored train has the advantage of all bogies being the same and all cars weighing the same (aprox) You can add other bits of equipment to any car and maintain the weight ratio. The big advantage is however, that a REGEN (not rheo) brake can be employed.

A train with trailer cars however saves on equipment costs aand is somewhat lighter overall.

[Phil]

q8 said:

A train with trailer cars however saves on equipment costs aand is somewhat lighter overall.

Including more lightweight bogies etc: reduced construction cost AND reduced running cost

[igelkotten]

As others have already said, it is in many ways a matter of swings and roundabouts, and the configuration you eventually choose is highly dependant on your local conditions and traditions.

One distinct advantage of having all axles motored is that the tractive effort can be spread out on more axles, thus leading to a much more even traction curve, with less problems with wheelslip and skidding. It can also be problematic for the ride quality if you have widely varying axleloads within the same train, with some (motored) bogies significantly heavier than others.

With a train where every axle is motored, there is obviously more equipment, and more things that can fail. On the other hand, losing traction from one bogie out of sixteen on a train is hardly a serious matter, whereas losing a single bogie out of five or six powered ones is a bit more serious.

One thing that at least in earlier times was important in deciding between an all-powered configuration and a trailer configuration is the cost of the control equipment, both to install and maintain. Modern solid-state power electronics are relatively cheap, very compact and can be built highly modular, thus making the control of say, eight powered bogies against sixteen, a relatively minor matter, once you have the basic traction and power conversion package installed.