steam loco question

[nw-mailing-list at nwhs.org]

I'll let someone else address the wreck, but the change in  superelevation I 
can address as an add-on to my previous  contribution.
 
If you think about it, it's intuitively obvious (and not hard  to calculate) 
that a particular combination of curvature and superelevation is  going to 
have only one ideal speed (ignoring for the moment differing locations  of the 
center of gravity and roll center).  Where mixed traffic at  different speeds is 
operated, you inevitably have compromises.  In the case  of the N&W in the 
mountains, the coal trains would tend to slip down  against the lower rail, 
increasing rail and flange wear as well as train  resistance.  Also, a long, heavy 
train stretched around a sharp,  superelevated curve has more of a tendency 
to "stringline", increasing the  possibility of derailments.  
 
So, once the passenger trains were gone, it made sense to lower  the 
superelevation to a value more consistent with the typical coal train  speeds.
 
Dave Phelps
 
   In a message dated 6/29/2006  11:26:22 P.M. Eastern Daylight Time, 
nw-mailing-list at nwhs.org writes:

 
 
What might not be related is what was told me regarding the famous  13-degree 
curve at Cedar, WV, by Bob Saxtan. It is that the superelevation of  this 
curve was lowered and the curve was tightened after the end of N&W  passenger 
service- what would be the reason for these modifications? 
I might note something that happened on the night of January 23, 1956. The  
611, running the Pocahontas westbound, wrecked there at 12:51 AM. During the  
wreck, the 611 tipped over on the curve, and seemingly "jumped" over the  
inside westbound rail of the curve, then grabbed one of the rails of the  eastbound 
track, which she pulled with her on her way onto the bank. I might  ask if 
any of you want to comment on how the 611 made this "jump" as she did,  even 
with the little room (as I have seen) between the curve tracks and the  bank as I 
have seen at Cedar. 
Lois J. Ponton 
Author of 611 wreck book "Midnight on the Pocahontas" 





 
____________________________________

From:  nw-mailing-list at nwhs.org
Reply-To:  NW  Mailing List <nw-mailing-list at nwhs.org>
To:  NW  Mailing List  <nw-mailing-list at nwhs.org>
Subject:  Re: steam  loco question
Date:  Tue, 27 Jun 2006 22:31:35 -0700  (PDT)


How was all of this effected by  superelevation of the track?
I have never totally understood why they  used it but it sounds like it would 
enhance the effect of the conical  wheels.  
Thanks,
Jim  Hall

nw-mailing-list at nwhs.org  wrote:

    
I won't repeat the answers given so far, which are all  correct and well 
explained, but there's two more factors, as it's been  explained to me over the 
years (I'm an old electron pusher, so I take  these things on faith): were not 
most steam locomotives built with a  certain amount of lateral motion allowed 
in 
the journal boxes?   Even thought the frame and bearings would hold the 
driving axles parallel,  the ability to shift laterally slightly would also help.  
Secondly,  while in the ideal case the conicity of the wheel sets would 
eliminate or  minimize flange contact, in the real world there is flange contact.   
As long as the angle of attack of the flange is small and the shape of the  
flange is correct, the wheel will not climb, but rather the flange  will keep 
the wheel in place.  The geometry of the flange  and rail head result in a 
measure called the "L/V" ratio, the ratio  of the lateral force (which tends to 
cause flange climb) to the vertical  force (which keeps the wheel in place).  I 
have read what a desired  limit of the L/V ratio is but I confess I didn't 
commit it to memory.  






Dave Phelps
 
In a message dated 
6/27/2006 9:16:08 P.M. Eastern     
  
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