Factors of Adhesion for the Big Three

[nw-mailing-list at nwhs.org]

Jerome,

The total engine weight of a J is 494,000 lbs.  This
is why I mentioned caution when looking up sources. 
Some of the variations in weight are due to different
modifications installed over the years, and others are
just plain errors.  In the J's case there's no
variation. N&W locomotive diagrams state 288,000 lbs.
WOD.

Passenger locomotives can have a fairly high factor of
adhesion.  PRR K4's were in the 4.5 to 4.7 range,
depending on the WOD (it varied).  The Milw A 4-4-2
had an FA between 4.63 and 4.7 according to the
sources I have.

Statistically, actual FA increases inversely with the
number of coupled axles.  In other words a 4-4-2 would
be higher, on average, than a 4-6-2/4-6-4, and they
would be higher than a 4-8-4.  There's a pattern to
this over a very large number of examples.  However,
individual examples within each wheel arrangement can
vary widely.

Don't attach  too much importance to the figure Factor
of Adhesion.  It's nothing more than a ratio.  The
figure 4.00 is considered a magic boundary by some,
but it isn't.  This much is certain: the higher the
number, the more surefooted the locomotive will likely
be.  But....N&W violated the 4.0 guideline all over
the place and was still outstandingly successful.  If
a RR can guarantee excellent trackwork, competent
handling, thorough preparation and maintenance, it can
operate locomotives that have an FA below the 4.0
level and not have problems.  N&W did just that. 
However, I have heard that sending a J out with wet
sand or plugged up sanders was not the best idea in
the world.

Dave Stephenson

--- nw-mailing-list at nwhs.org wrote:


> My reference gave the J's weight on drivers as

> 494,000, and boiler pressure  

> as 300 psi.

> Also; have to question the starting FA of 3.44 for

> the Y6b.  Usually  

> associate lower FA value

> with high speed passenger locomotives, such as

> Milwaukee Road's  

> semi-streamlined 4-4-2 

> of the mid 1930's.  Would expect heavy freight

> locomotives, such  as the Y, 

> to have FA of

> 4.00 or higher.  

>  

> Jerome Crosson    

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