Balancing, Counterbalancing and Dynamics

[NW Mailing List]

Remember that the counterbalancing is not for a STATIC case but a DYNAMIC
case with the mass of the drivers and rods included and rotating at
different speeds.  In addition there are first mode, second mode, third mode
and so on, that is, different dynamic loading per frequency at multiples of
the running rpm.  Depending on a bunch of different things, the second,
third fourth or other modes might be the most significant loading comparing
a dynamic loading situation to a strictly static one.  In reality, you have
the rotating drivers plus the oscillating rods moving back and forth and
going around the driver pin so those loads are part rotating and part
horizontal and vertical loads. Plus the loads from one side are transmitted
to the other side and vice-versa.

 

Thinking about the situation in 'common sense' static balance thinking is
pretty far off from what actually happens in a dynamic situation. 

 

In physics or vibration calculations/modeling, this is a complex system
requiring some pretty sophisticated analysis.  The Roanoke engineers would
have loved to have had a computer to model what they had to estimate with a
slide rule.

 

Part of the issue with the RF&P 4-8-4's and their poor high speed balancing
problems were that the published state-of-the-art calculation methods didn't
work (1927).  The N&W didn't do the calculations that way for the A and the
J.  (The AT&SF engineers didn't follow the published methods either for
their high speed locomotives.) 

 

Gary Rolih

Cincinnati ( and a Mechanical Engineer)

 

 

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From: nw-mailing-list-bounces at nwhs.org
[mailto:nw-mailing-list-bounces at nwhs.org] On Behalf Of NW Mailing List
Sent: Wednesday, March 25, 2009 3:54 PM
To: NW Mailing List
Subject: Re: Wheel spokes

 

Very interesting.  I had always assumed that counterweights were centered
exactly opposite the pin holding the rods.  While that appears true for the
front and middle A drivers, it is obvious from the drawing that it is not
true for the main driver.  Would this be because the added weight of the
main rod throws the balance off-center?

 

Sam Putney

 

----- Original Message ----- 

From: NW <mailto:nw-mailing-list at nwhs.org>  Mailing List 

To: NW <mailto:nw-mailing-list at nwhs.org>  Mailing List 

Sent: Monday, March 23, 2009 8:20 PM

Subject: Re: Wheel spokes

 

Richard,

I'm surprised no one else has answered this yet. The number is 15. 

You can see drawings of the drivers at the following addresses:

Front Driving Wheel http://www.nwhs.org/archivesdb/detail.php?ID=23293
Intermediate Driving Wheel
http://www.nwhs.org/archivesdb/detail.php?ID=23187
Main Driving Wheel http://www.nwhs.org/archivesdb/detail.php?ID=23192

Listing of more Class A wheel drawings is at
http://www.nwhs.org/archivesdb/listdocs.php?index=rs
<http://www.nwhs.org/archivesdb/listdocs.php?index=rs&id=161&Searchword=whee
l> &id=161&Searchword=wheel 

Ron Davis

At 03:15 PM 3/20/2009, you wrote:



Hi chaps
Can somebody tell me the exact number of spokes on a Class A driving wheel,
thanks in advance
 
Regards Richard in UK
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