Re: C Class Rumours

[G.Lambert@unsw.edu.au (Geoff Lambert)]

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