Hi Gregory
On (15 May 97) Gregory Procter wrote to Alec Cameron...
 GP> I can't let this one go by!!
 GP> The pulling power of a locomotive is a function of the weight of the
 GP> locomotive
 GP> drivers on the rails (assuming the gearing is not arranged for ultimate
 GP> speed)
And is compromised by a few other things- like the fact that with coupled
drive wheels, a slip on greasy or leafy rails leads to almost total loss of
traction.  Diesels and elecs having independent drive to each axle, some may
grip while others slip and a decent drawbar pull is maintained by the loco as
a whole. Then there is the beaut feature of positive creep whereby even more
traction is obtained by deliberate, micro slippage possible thanks to
microprocessors.
 GP> The horsepower rating is more indicative of the maximum speed that the
 GP> locomotive can maintain with its rated load than the size of the load
 GP> itself.
However few locos are allowed to run steadily at optimum speed. In the real
world it is stop, start, retard, accelerate. Steamers do not take so kindly 
o
this and that is why for locos of comparable HP, the steamer achieves lower
average speeds over a duty cycle, than do the diesels/ elecs.
 GP> The British tended to keep steam from electrified lines because of the 
low
 GP> mounted overhead wires and the perceived danger of flash-over.
I wonder if there ever WAS a flashover. Many's the time I have looked at the
blast of steam and unburned carbon from an engine at low speed and wondered
how the HV insulator above being so blasted, could possibly survive.
                                                                    
 GP> Steam locos could often start heavier trains than diesels or electrics
 GP> (comparing equivalent total weight on drive wheels) because diesels and
 GP> electrics are limited in the amount of current they can pass through 
their
 GP> axle motors from starting. A small steam shunter might start twice the
 GP> weight
 GP> that an equivalent diesel electric shunter could.
For that to happen, would earn the elec designer a thump for not doing his 
ob
right. Every NSW diesel/ elec loco I have known of was limited at start from
rest, by the wheel slip threshold not the armature current. Maybe the cases
you know of, were misapplication where passenger locos were having to slog in
freight or switching service. It is common for different gearing to be used
so that freight locos motors get to spin faster at low road speeds, assuring
quicker acceleration and enhance the motor shaft cooling fan output.
The 3780HP one I bragged about, had a bit of my own [trivial] design work in
it. For long distance coal traffic on a mountains route, these were provided
with two ducted blower motors in the body. I designed the rivet pitching on
the drivers' doors!
No I did not forget turbine power. Nor accumulator battery drive. Nor Kitson
Still. Nor Atmospheric Railways. Interesting experiments, successful in some
very small scale applications but catch on they did not!!
 GP> Ok, I vote for steam :-)
I love ugly ducklings too! Cheers......ALEC
...         Me drive? I'll take the train as the good Lord intended!  ^oo  
oo^oo   oo^
...         Me drive? I'll take the train as the good Lord intended!  ^oo   
oo^oo   oo^
--- PPoint 1.92
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