Re: Re:W braking

Hi Bob,

You are right about them not getting away from lights because of the doors,
it really is a cock up of an idea, as for the added weight, I think that is
less of a problem as, when empty, the machine and counter weight don't come
near a full load, the doors are the main problem.

My mention of the braking maybe a little inaccurate and purely from my own
years of experience of driving all types but, the W, being slower and
lighter than the modern cars, can pull up in a very respectable disance when
required to, remember, I used to have to demonstrate this to every new
student when I trained them. I would always grab a car waiting to go on the
grinder for flats to do this. I have "thrown out the picks" to avoid moron's
in cars etc., in modern cars and been surprised at how long they can take to
stop compared to a W. If a W went at the same speed, now that would be a
different picture! Out of curiosity, Peter E, I assume you have had to test
the 4th emergency on the Milan cars (I think you call it "slugging"), what
do you think compared to an LRV, not a PCC as I think, with a weight similar
to a Witt (or W for that matter) it would pull up quicker. By the way, if
you were talking about a Z1 or Z2 against ANYTHING else, my money is on the
Z, they were dynomite!!

Cheers
Greg

Actually, acceleration is quite important so you can get out into the
intersection before the light turns red.

Unfortunately the "W"s that have been half-assed converted for one man
operation have several problems in getting away from tram stops in time to
catch traffic lights.

One is the extra weight of the ticketing machine which, with its
counterweight, has appreciably slowed the rate of acceleration.

The other is the door interlock. W class trams used to have their doors
opening as they came into the stop and their doors closing as they
accelerated away from their tram stops. They can't do that anymore and it
must cost 4 traffic lights a trip on most lines, sometimes more. That's 4

minutes per trip, each way...

Centre entrance cars are not ideal for OMO.

As for the notion that a W class tram can stop as fast as a modern tram.

Physically impossible.

Even with sand down, the friction coefficient of steel on steel and the
limited contact area between wheels and rail limit maximum rate of
deceleration.

The main advantage of a track brake, whether it be mechanical (like cable
cars) or electromagnetic is that it increases the contact area and that
increased area is made up of a higher friction coefficient surface (in the
case of a pine block track brake a la cable trams, they can get slick in

the

wet when they absorb water so then need sand under them to work

effectively.

They actually can cause the wheels to skid because they take some of the
tram's weight off them.).

Bob Murphy

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