Re: C Class Rumours

[mauried@commslab.gov.au (Maurie Daly)]

In article <7n0imq$3kg$1@mirv.unsw.edu.au> G.Lambert@unsw.edu.au (Geoff Lambert) writes:
>From: G.Lambert@unsw.edu.au (Geoff Lambert)
>Subject: Re: C Class Rumours
>Date: Tue, 20 Jul 1999 00:28:39 GMT

>David Johnson <trainman@ozemail.com.au> wrote:

>>Keith Malcolm wrote:

>>> The "dead" weight of a steam loco is no water in the boiler and an empty
>>> tender. The "live" weight is a full tender and 3/4 full boiler.

>>Not necessarily.  If a steam locomotive was to fail climbing Molonglo Gorge and need to be pushed
>>out by the Exploder, the tender would be full, as would the boiler.  How heavy would it be?  How
>>much resistance would the Pistons have?

>I don't think the practice described here for engines with traction
>motors was ever adopted for steam.  I have heaps (hundreds) of WTT's
>in my collection, and I've never noticed anything like this for steam.
>(But then, I never noticed that a dead diesel was heavier than a live
>one either and I have all the NSW WTTs 1950-1998)

>However, the usual formulas for loss of power at any particular speed
>for steam locomotives assumed that this was about 8% between the
>piston and the wheel.  This power, consumed in friction, etc., had an
>equivalent manifestation as a force.  It is at least partially valid
>to turn this idea around and work out the force offered by the
>machinery when a loco is moving "dead".  For a 38-class, one would
>expect a force of about 3,000 lb on this basis.  The next step, to
>equate this to a notional increased mass, is just about as dodgy as it
>is in doing so for a diesel electric, because the whole thing is speed
>and grade dependent.  Indeed, I would say to do so is meaningless, and
>I really think the practice for diesels is meaningless too (if that's
>the rationale behind it for diesels, which it mightn't be).

>But, if we assume that the total resistance (including air) of a
>38-class, in lb/ton is given by the "Abbot formula"  of R = 5 +
>0.003*V *V, where V is in mph and we assume the 38-class is about 195
>ton (I forget exactly what it actually is), then 3000 lb represents
>the resistance at about 55 mph.  But I don't know how to translate
>this back into "equivalent dead weight"

>All of this assumes that the wheels remain connected to the pistons
>during "dead-haulage" and that the valves are set so that
>counter-pressure doesn't develop in the cylinders.  Neither is
>necessarily true.

>Geoff Lambert


Your pretty right Geoff in that most of the argument is academic these days.
The worst case scenerio for DE hauled train with a "dead" loco attached is 
trying to start with full load on a severe grade , ie the full load is set by 
the grade.
Locos of 2000 HP and over with axle loads of less than 23 tonnes have 
sufficient starting torque to spin the wheels if too much power is applied.
The dead loco in this case supplies an additional starting load in that we 
must suuply enuf pull to overcome the inertia and brush pressure of the 
stationary traction motors.
If you try to spin any large DC series motor , even a car starter motor will do
you will find that the initial resistance to movement is higher than when you 
actually get the motor spinning