PCC Speed

[Jim Holland]

Greetings!

	A million thanks, Fred, for taking the time to write such a wonderful
clarification to PCC speed.  I guess it is part of our *inhuman nature*
to be prejudiced *for* our favorite topic - and thus grossly exaggerate
its performance and benefits!

	By the way, when you were in San Francisco in 1980(?) and I was
operating PCC 1040 down thru the Twin Peaks Tunnel on the ERA Charter,
how fast do you think we were going?  I doubt we reached 42!  But Mr.
Geissenheimer commented that he enjoyed the ride!
	I had worked with the line crew one evening in the tunnel and observed
the PCC wire in addition to the separate LRV wire.  It was interesting
to note that the wire was most worn coming off a hanger - seemed the
pole would bounce coming off a hanger and this caused more wear. 
Because of this I was afraid to really open it up (like I had done with
other cars!) but I wanted to give the trolley fans a good ride. 
Additionally, the dynamic governor was strong and everytime I released
the power we slowed considerably!
	At that time, I was working the N JUDAH on a regular schedule and was
the second car out of the barn on Sat and Sun.  I always got a Baby Ten
(1016-1040) car, similar to the PRCo 1700-1724 series.  A couple of the
fans rode my car that weekend.  When I went into the Sunset Tunnel
inbound (downhill, about 3/4 mile) I always put it to the floor and
never released the power until I absolutely had to; think we were moving
pretty fast then!

Fred Schneider wrote:
> 
> I once raised the question of speed with an electrical engineer at GE
> ... back in the late 1970s when I was working on the PCC books.
> 
> The 42 miles per hour balancing speed was calculated in 1936 based on GE
> 1198A1 or Westhouse 1432 motors, both internally ventilated, and a
> 36,000 pound car on level, tangent track, with 550 volts.  I do not
> remember if it also included a seated load, which would add another 8000
> pounds.  Transit Resarch Corporation once printed (and I have no idea
> where I put it) a graph showing balancing speed in relation to gradient
> ... it is somewhere in the tons of paper at home.  I think the balancing
> speed was down around 15 miles per hour on a 10 percent grade, maybe 12
> miles per hour on the steepest part of the Fineview line.  Therefore
> your guess of 28 miles per hour up the 6% grade through South Hills
> Tunnel is probably close.
> 
> The balancing speed (that at which the counter EMF generated in the
> motor matches the voltage imposed on the motor) would of course vary
> with gradient, load, curve friction, and voltage.
> 
> The 1936 car would accelerate at peak rate of 4.75 miles per hour per
> second until in reached approximately 15 miles per hour ... enough to
> get through the intersection ahead of a Chevy with a flathead six.
> Above 15 miles per hour, the acceleration curve began to taper.  It was
> quite normal to get to 25 miles per hour within one city block.   The
> car simply was not designed to run full bore ... it was designed to
> "float" in traffic which customarily moved at 25 to 30 miles per hour.
> It had very brisk acceleration at lower speeds.
> 
> How long did it take to get to 42 miles per hour?  Over 30 miles per
> hour, the acceleration curve was virtually flat. And the faster the car
> went, the weaker acceleration became.  A PCC would accelerate to 30
> miles per hour in about a city block (normally considered about 0.1
> mile) but it took almost a full mile to get up to 42 miles per hour.
> 
> So the chap who told me he chased one across Philly's Chestnut Street
> bridge at 55 probably caught up to the car!  My memories of going like
> hell over the 6th Street Bridge in Pittsburgh were probably affected by
> the sound of the bridge itself drumming ... when I go back and drive
> over the bridge today, and realize the gradient approaching it and the
> braking time needed to stop at Fort Duquesne Way at the other end, I
> suspect top speed wasn't anywhere near 40 ... 20 might be more like it.
> And those 60 or 70 mile per hour rides in the New York subways?  The
> fastest express trains ran somewhere near 45 miles per hour!
> 
> Shaker Heights cars had 1 inch larger wheels ... balancing speed might
> have been about 44 miles per hour and maybe they got to 50 inbound from
> Shaker Square with a swinging load in the morning rush. But it was
> probably more like 30 coming out in the evening.
> 
> There are some long downhill stretches on Boston's Riverside line ...
> maybe something over 42 was also possible.
> 
> You must also note that, like reptilian evolution, the PCC got heavier
> over time.  The original Brooklyn cars weighed around 35,900 pounds.
> Top weights reached 11 percent more than the original figure, which
> would also lower the balancing speed.  And how about the weight of paint
> (this didn't apply to Pittsburgh) but Philly cars probably grew much
> heavier over time simply by adding pigments.  The use of blown motors
> after 1940 may have slightly raised the speed and compensated for the
> heavier cars.
> 
> But for the most part, the fish gets longer with each narration.

James B. Holland
------- -- ---------
        Pittsburgh Railways Company (PRCo), June of 1949 -- June of 1953
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