Re: [SFMuniHistory] Digest Number 623
Jim Holland
Monday, April 29, 2002 4:55 AM
Good Morning!
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I believe Mr.David McLoughlin is a journalist in New Zealand. While well
intentioned, his information can be way off the mark many times.
Disclaimer:: This is an Imperfect world, and there shall always be
exceptions for one reason or another, but the following is generally true.
Trolley pole bases are 1)--over the king-pin of the rear truck (single-end
equipment but also true of double-end equipment) OR 2)--located 2-3 feet
Ahead of said Kingpin; the latter seems to be the most common. This
necessitates a trolley pole length of about 12-14-feet which brings the
pole to slightly beyond the end of the car when hooked down; when the pole
is on the wire at nominal height, it is then positioned directly above the
end of the car.
When a trolleycar negotiates a sharp turn, the trolleypole base is
1)--*just-barely-inside* the radius-line of the turn (radius is measured
to the center of the track between the two-rails) when the base is
immediately above the kingpin to 2)--*just-inside* the radius-line of the
turn when the base is mounted forward of the kingpin. THUS::: The
trolleywire is in a similar position above the track; i.e., just inside the
radius-line of the turn. If it varies much from this then the wire
receives excessive wear from the flanges of the wheel//shoe.
.......AND the trolley-pole moves very little in reality if one stops to
think of what is happening. When beginning a sharp turn, the trolley pole
wheel//shoe is the last item to leave the tangent so the trolleycar is
actually turning Underneath the trolley pole and the back-end is swinging
away from the trolley pole! Yet common talk is about how far out the pole
swings when that is not the case at all - just looks that way ---
appearances can be deceiving! On the turn itself the pole moves to and
fro slightly between hangers. The biggest move for the trolley pole is
leaving a turn -- the trucks are on tangent track but the trolley pole is
still on the turn and has to move back over the center of the car. Track
switches and the placement of frogs above the same cause some movement of
the trolley pole as well.
So David's statement above about the trolleywire for trolley poles being
much further inside for proper tracking is incorrect.
When pans displace trolleypoles, there is a transition period where both
will be in use. THUS::: pans need to be mounted so that when the carbon
is against the overhead that this portion of the pan is just above or
slightly ahead of where the trolley pole base would be. This will keep
the carbon in the center of the pan at a hanger or pull-off.
Trolley poles need more pull-offs on turns than do pans to make a smooth
transition and turn but not all systems follow this. PRCo was extremely
good at making smooth turns; LATL was the absolute Best bar none!(:->)
San Francisco used less pull-offs on turns *Before* lrvs were
introduced. Had the former wire been changed to accept pans without more
pull-offs, this would *probably* have suited the pans as well and made a
little more uniform wear on the pan carbon.
If a system is built from scratch for pure pantograph usage, then the
trolleywire is staggered not only on tangent but also on turns to maximize
uniform wear on the carbon. For discussion purposes, lets say the contact
surface of the pan is 6-feet wide - that makes 3-feet of contact on either
side of center. Thus on turns, all hangers would be placed aprox.
2.5-feet *Outside-the-turn-Radius* and would be spaced far enough apart
so that the wire at midpoint is 2.5-feet *Inside-the-turn-Radius* which
allows for uniform carbon wear. A trolley pole *might* negotiate this if
the car is operated gingerly thru such a turn, but more than likely it
would dewire as well as cause excessive wear.
Parts of the 24-Divisadero line were strung similarly when it was
converted from diesel to trolley coach and some of this has been replaced
with the standard span.
____________________________________________________
<><><><><><><><><><><><><><><><><><><><><><><><><><>
James B. Holland
Holland Electric Railway Operation.......
___"O"--Scale St.-Petersburg Trams Company Trolleycars and...
______"O"--Scale Parts mailto:[email protected]
______Pennsylvania Trolley Museum http://www.pa-trolley.org/
___Pittsburgh Railways Company (PRCo), 1930 -- 1950
N.M.R.A. Life member #2190; http://www.nmra.org
<><><><><><><><><><><><><><><><><><><><><><><><><><>
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____________________________________________________
____________________________________________________
From Dave McLoughlin:
The poles follow the pan-staggered wires without any obvious
problems that I have ever seen, even on curves, where the wire must
be close to the centre for the pans, but where in pre-pan days, it
was much more off-centre on curves to assist the pole's tracking.
I believe Mr.David McLoughlin is a journalist in New Zealand. While well
intentioned, his information can be way off the mark many times.
Disclaimer:: This is an Imperfect world, and there shall always be
exceptions for one reason or another, but the following is generally true.
Trolley pole bases are 1)--over the king-pin of the rear truck (single-end
equipment but also true of double-end equipment) OR 2)--located 2-3 feet
Ahead of said Kingpin; the latter seems to be the most common. This
necessitates a trolley pole length of about 12-14-feet which brings the
pole to slightly beyond the end of the car when hooked down; when the pole
is on the wire at nominal height, it is then positioned directly above the
end of the car.
When a trolleycar negotiates a sharp turn, the trolleypole base is
1)--*just-barely-inside* the radius-line of the turn (radius is measured
to the center of the track between the two-rails) when the base is
immediately above the kingpin to 2)--*just-inside* the radius-line of the
turn when the base is mounted forward of the kingpin. THUS::: The
trolleywire is in a similar position above the track; i.e., just inside the
radius-line of the turn. If it varies much from this then the wire
receives excessive wear from the flanges of the wheel//shoe.
.......AND the trolley-pole moves very little in reality if one stops to
think of what is happening. When beginning a sharp turn, the trolley pole
wheel//shoe is the last item to leave the tangent so the trolleycar is
actually turning Underneath the trolley pole and the back-end is swinging
away from the trolley pole! Yet common talk is about how far out the pole
swings when that is not the case at all - just looks that way ---
appearances can be deceiving! On the turn itself the pole moves to and
fro slightly between hangers. The biggest move for the trolley pole is
leaving a turn -- the trucks are on tangent track but the trolley pole is
still on the turn and has to move back over the center of the car. Track
switches and the placement of frogs above the same cause some movement of
the trolley pole as well.
So David's statement above about the trolleywire for trolley poles being
much further inside for proper tracking is incorrect.
When pans displace trolleypoles, there is a transition period where both
will be in use. THUS::: pans need to be mounted so that when the carbon
is against the overhead that this portion of the pan is just above or
slightly ahead of where the trolley pole base would be. This will keep
the carbon in the center of the pan at a hanger or pull-off.
Trolley poles need more pull-offs on turns than do pans to make a smooth
transition and turn but not all systems follow this. PRCo was extremely
good at making smooth turns; LATL was the absolute Best bar none!(:->)
San Francisco used less pull-offs on turns *Before* lrvs were
introduced. Had the former wire been changed to accept pans without more
pull-offs, this would *probably* have suited the pans as well and made a
little more uniform wear on the pan carbon.
If a system is built from scratch for pure pantograph usage, then the
trolleywire is staggered not only on tangent but also on turns to maximize
uniform wear on the carbon. For discussion purposes, lets say the contact
surface of the pan is 6-feet wide - that makes 3-feet of contact on either
side of center. Thus on turns, all hangers would be placed aprox.
2.5-feet *Outside-the-turn-Radius* and would be spaced far enough apart
so that the wire at midpoint is 2.5-feet *Inside-the-turn-Radius* which
allows for uniform carbon wear. A trolley pole *might* negotiate this if
the car is operated gingerly thru such a turn, but more than likely it
would dewire as well as cause excessive wear.
Also interesting that Melbourne went big in the 1970s and 1980s with
synthetic parafill span wires (as used extensively in Europe) which
do not need insulators and are thus less visually "obtrusive." But
apparently they had some bad experiences with sagging over time,
Parts of the 24-Divisadero line were strung similarly when it was
converted from diesel to trolley coach and some of this has been replaced
with the standard span.
David McLoughlin____________________________________________________
Auckland New Zealand
____________________________________________________
<><><><><><><><><><><><><><><><><><><><><><><><><><>
James B. Holland
Holland Electric Railway Operation.......
___"O"--Scale St.-Petersburg Trams Company Trolleycars and...
______"O"--Scale Parts mailto:[email protected]
______Pennsylvania Trolley Museum http://www.pa-trolley.org/
___Pittsburgh Railways Company (PRCo), 1930 -- 1950
N.M.R.A. Life member #2190; http://www.nmra.org
<><><><><><><><><><><><><><><><><><><><><><><><><><>
------------------------ Yahoo! Groups Sponsor ---------------------~-->
Buy Stock for $4
and no minimums.
FREE Money 2002.
http://us.click.yahoo.com/k6cvND/n97DAA/ySSFAA/DiTxlB/TM
---------------------------------------------------------------------~->
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/