A's on the WMB

[Craig Haber <albatross@harnessnet.com.au>]

G'day,

Due to B61 having radio repairs at Dynon, V/Line freight loco A77 hauled
8207/46 on 9/3, and A81 hauled 8207 (and I expect it returned on 8246)
on 10/3.

I was the Conductor on 8246 on 9/3, which gives a chance to compare the
performance of some different loco's.  

Here's the running times from some different trains, note the loco and
dates are presented
below.  I've used similar train consists.  The A had 5 cars, one PCP and
one CP, I haven't run a train like that with a WCR loco (all have had
only 1 van), so I've presented runs with 5 and 6 cars for comparison. 
Number of pass cars (in brackets) follows the loco number.

Note all are train 8246 Mon-Fri, except for A77's run (Sunday 8246
timings are used on Public Holidays), which includes a stop at
Birregurra, and different schedule (schedule sectional times in
brackets).  I haven't included times north of Geelong, as the public
holiday timetable only stops at Werribee, the weekday 8246 stops at Nth
Geelong, Corio, Lara, Werribee, Footscray, so obviously you can't
compare apples with oranges!

		A77(5)		S302(6)		S311(6)		B61(6)
Date		9/2/98		11/11/97	12/11/97	15/12/97
WMB-TEG		30 (29)		31 (32)		31		33
TEG-CDN		14 (15)		14 (14)		14		15
CDN-XCO		27 (26)		26 (27)		27		28
XCO-WIA		stop BGU	25 (25)		25		25
WIA-GEX		25 (31)		26 (29)		25		25

Section		B76(5)		S311(5)		B61(5)		S302(5)
Date		15/12/97	17/7/97		21/8/97		13/11/97
WMB-TEG		31 (32)		31 		32		31
TEG-CDN		15 (14)		14 		16		14
CDN-XCO		27 (27)		26 		27		26
XCO-WIA		24 (25)		25 		25		25
WIA-GEX		30 (29)*	27 		26		25
* includes stop of 2 mins at Sth Geelong to set down a group.

I haven't ever run an 8246 with S300 on 5 or 6 cars, but it's
performance is similar to that of B76.

You'll notice there's not much difference from loco to loco, and there's
some inconsistency, acc. difference in crews and conditions.  The above
were not determined from a scientific
experiment with controlled conditions - they are simply time logs from
my Conductor's log
books, hence they are a representative of what you can expect in general
day to day
operation of the railway.  When a controlled experiement was conducted,
of S Vs N, with
same load and same driver, the S was 4 mins faster both ways.  I'll try
and dig out the time
logs before I go on leave.  An A should outperform an N, it is lighter,
and more aerodynamic.

S302 is perceived to be the best performer of the WCR fleet, with S311
not far behind.  Note
however that S302 is on full wheels, S311 is on minimum wheels, hence it
has to work
considerably harder.  When it receives it's new bogies (currently under
overhaul at Ballarat
East) it may well out-perform S302.  I have been told (by some drivers)
that B61 is virtually
the equal of an S class in performance, I understand it is lighter than
it's sister units.

But why is the turbocharged A class not a significantly better
performer? It enjoys a 700hp
advantage over an S (+39%), and 1000hp over a B (+67%).  I discussed
this with our
Workshops manager, who was involved in the testing on N Vs S class in
early days of WCR
operation.  In short, the answer lies in the turbocharger, and the
nature of the Warrnambool line.

The Warrnambool line is relatively flat - i.e, there is no sustained
climbing, most grades are short and sharp.  There are also a lot of
speed curves.  So by it's nature, it's an "open throttle, close
throttle" type line, that is, the drivers are opening and closing the
throttle
regularly.  This presents a problem to any turbocharged engine, due to
the turbo lag.  When opening the throttle (to accelerate out of a speed
curve for example), a percentage of the engine's output is dedicated to
getting the turbo up to speed, rather than moving the train.
This consumes fuel, and restricts horsepower until the turbo comes into
it's optimum range, at which point it goes from having a negative, to a
positive effect.  In short, you never get the most out of a turbocharged
loco on such a line.  On something like the Bendigo, or Ballarat
where there is sustained climbing, you put the loco in notch 8, get the
turbo up to speed and maximum engine output, and leave it there - you
don't waste any further time/fuel accelerating the turbo.  No turbo lag
on a roots blown loco, you open the throttle, and it's power (and fuel
consumption) all goes into moving the train.

Hence despite having smaller and less powerful engines, an S or B on the
Warrnambool can match the performance of a nominally more powerful
loco.  And despite being an older design engine, by virtue of being
smaller and by putting more output into moving the train (rather than
winding up the turbo), the fuel consumption is much the same.

There was some discussion about the role of the roots blowers in these
engines in this newsgroup - again speaking with our fitters at Ballarat
East, they tell me the roots blower *does* supercharge the engine,
although only very mildly.  Yes it does also scavenge the
exhaust gas from the cylinder.

I have a time log I took from A73 on an N set back on 16/2/93, I'll dig
out some runs with WCR S/B's on 3 cars and see how they compare some
time.  

Cheers,
Craig.
-- 
Craig Haber
albatross@harnessnet.com.au
Manufacturing Systems Engineer (almost) 
Web Page Designer, Harness Racing, Railways, and Essendon Football Club
fanatic
http://www.harnessnet.com.au/