[PRCo] Re: Pittsburgh B-3 Trucks

[Fred Schneider]

I have never seen a recomputed value.  It was done once in 1936.  Please
note, Derrick, that balancing speed depends on several variables: weight,
gradient, curvature and voltage.  I think the calculation for the PCC
motors was based on 550 volts, seated load, and level tangent track.
Obviously, the balancing speed drops precipitously for a car on a 12
percent grade in the middle of a 40 foot radius curve with a standing load
in the rush hour when there are dozens of other cars pulling the voltage
down.  I once saw a chart for grades ... I think a car on Henderson Street
on the Fineview line could achieve a maximum speed of 15 mph if you had
forever to get there.

Now that we've thrown in all the variables, it might be obvious to you that
the PCC car weights increased over time, which caused the balancing speeds
to drop.  Repeat changed balancing speed (which is the point when counter
emf prevents the car from going faster).  The variables may or may not
change acceleration, as I'll explain later.  The Brooklyn cars in 1936
weighed 33,180 lbs and that is the car for which the balancing speed
calculations were made.  The Pacific Electric cars make a good example of
change ... add length, add seats, add people, add couplers ... you had cars
that were five feet longer than the prototypical PCC and weighed 41,600
lbs.  How much did this affect the running speed?  Don't know.  But it sure
as hell had an affect.

Changing the wheel diameter would increase the balancing speed but also
lengthen the time it takes to get to that speed.  The Shaker Heights cars
had wheels that were an inch larger than standard and which would increase
the theoretical balancing speed by 4 percent to about 43.5 miles per hour.
However, the Shaker Pullmans weighed in at 43,100 lbs.   It would seem to
me that the designers were looking to protect motor armatures on the long
down hill freom Shaker Square more than how fast the cars would run
normally, because everything you gained going down hill would be lost
coming out, and the cars were heavy enough as it was.

The next consideration is that most cars increased over time.  Pittsburgh
100 weighed 34,300 lbs.  The Westinghouse tens were 475 lbs. heavier.  The
elevens added another 325 lbs.  The twelves added another 900 lbs.  And so
forth.  By the time you got to the 1700 city cars, the weight had risen to
37,423, more than 9 percent heavier than 100.  Obviously a car that weighs
a ton and a half more than 100 isn't going to run as fast.  The effect of
the weight may have be felt more in the top speed (balancing speed) than in
the acceleration rate.  I would imagine that the limit relay on some of
these heavier cars could be set for faster acceration because most cars
after 1940 had blown motors which could withstand a greater overload
without frying.   (A paint job adds a few hundred pounds too but Pittsburgh
was never guilty of that.)

I've never seen a balancing speed chart for the Red Arrow cars.  They had
75 hp Westhinghouse 1433 motors compared to the 55 hp machines on a PCC.
I've heard all sorts of rumors about them too.  Supposedly a story by a cop
who had a friend who was a PCC motorman with whom he would have 75 mile per
hour races out on the West Chester Pike late at night.  The man who told me
the story was a foamer.  I have seen data for the PST 70 cars (like 78 at
Arden) that showed a maximum speed of 55, much lower than even I wanted to
believe.  Without the field shunts (the way it is configured at Arden now)
it might be 40ish.  My suspicion is that the newer Brilliners and St. Louis
cars might truthfully have been in the same range with some downhill bursts
of faster running.  Cars 14 and 24 have had the acceleration limit relays
changed at Arden  so that "Fast Freddy" can't run them as fast as he would
like ... I might have had one of them up into the high 30s at the museum.
My best memory on the West Chester Pike was my father overtaking a Red
Arrow St. Louie ... probably took him a mile.  (Maybe it was less than a
mile ... fish always get bigger.)  Now let's look at this analytically.  It
was Sunday afternoon and Dad was out for a drive.  How fast would he have
been going.  My father, like all kids, was said to be wild in his youth but
his driving had become very conservative by the middle 50s ... he was in
his late 40s then.  He had no place to go.  No hurry.  He was driving an
abolutely gutless 52 Ford which he had specially ordered with a six
cylinder engine and Fordomatic.  That damn car had trouble catching up to
its own shadow.  I doubt very much if Dad was driving more than 50 and
knowing him 40 sounds a whole lot more realistic.  So, from the time I
first see the trolley ahead of us, it makes one stop, and dad passes it a
mile down the road at the next stop.  Sound to me like the PST car was
doing something in the middle 50s tops.

Derrick J Brashear wrote:

> On Fri, 3 Oct 2003 rogertrolley.1 at juno.com wrote:
>
> >
> > Jim Holland Commenting about 42 mph top speed for the PCC's brings up
> > the speed subject again. I belive most PCC's were quite capable of
> > reaching speeds in excess of 42mph.
>
> Vague recollection: didn't some of the propulsion packages have a 47mph
> balancing speed?

xx