Re: [Phys-L] train stopping distance

["LaMontagne, Bob" <RLAMONT@providence.edu>]

Yes, There is only so much air stored in cylinders on each car to be used for the mechanical brakes. Regenerative braking using resistor banks on the tops of the diesel electric locomotives helps save the air for use in emergencies. That type of braking is only for the locomotives. 

Full emergency braking of the entire train takes time. A wave of pressure drops initiated at the locomotive must move through the train. Then the brakes are applied to each car as the pressure drops on that car. There is a limit to how hard the brakes can be applied or else the pads would burn out. As John pointed out, the wheels do not lock in "full emergency". If the air is dumped, it takes a long time before it can be pumped back up and the train can proceed with usable brakes again. It is done this way so that a break in the air line does not result in a runaway train.

Bob
________________________________________
From: Phys-l <phys-l-bounces@www.phys-l.org> on behalf of Bernard Cleyet <bernard@cleyet.org>
Sent: Friday, June 24, 2016 9:56 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] train stopping distance

> On 2016, Jun 24, , at 14:20, LaMontagne, Bob <RLAMONT@providence.edu> wrote:
>
>  Moving tonnage by rail is remarkably efficient.


At one time (presently?) diesel electrics would use engine braking using huge resistors on the top of the engine(1).  Replaced by tons of battery would add significantly to that efficiency?


bc has a Prius.


(1) Heard train staff joking about fried birds, possibly was leg pulling.

Fermi question:  Is the energy regeneration > the energy to haul the batt. up the Rockies?  Is there a crossing weight and advantage?


p.s.  I think boat is E > rail.     Why so many canals?
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