Fwd: [steam_tech] DPM convincing?

[NW Mailing List]

I'm not sure how this posting got here but it has appeared on several other sites over the past month or so.  I believe William Wendt is the original author, and perhaps forwarded it from the Steam tech site to this board.

I posted the following response on both the Trains Magazine and Steam Tech sites:

The N&W A averaged 72,000 lbs on each driving axle. Don't know where
DPM got his figure.

The best I can do on an estimate of a Class A's capacity on level
tangent track, at the total evaporation and firing rate N&W
expected, is about 4,200 trailing tons at 60 mph. This reflects a
maximum of about 5,550 DBHP at 40 mph, the usual high point on an
A's DBHP curve

N&W rated its locomotives very conservatively, and the often quoted
5,300 DBHP is usually considered at the rear of the aux. water tank.
Toward the end of steam, the A's were developing slightly more than
this in order to get 16,000-18,000 ton trains from Williamson to
Portsmouth in something less than 4 hours. That's where the 5,550
figure comes from.

There are many examples of A's running a steady 60 mph on time
freights nos. 84 and 85 (some of O Winston Link's recordings), but
I've not been able to directly relate a trailing tonnage figure to
this speed. As a result, the above estimate is derived from Davis
equations commonly used by the RR industry during the 1950's.

Using the same estimating method as above, I changed the tonnage to
4500 and the grade to -0.022%, the average downgrade from
Williamson to Portsmouth. The estimated maximum speed was 60 mph. An
A didn't average this speed from point to point. This is the best
guess I can make as to why the A was rated at 4500 tons Wmsn-Ptsmth.

I believe that things were changing after 1958 and faster train times weren't as important to the new management as they were to the old. It take a lot more DBHP (and $) to run 60 than it does 45, and maybe the average point to point speed wasn't that much different. So if two GP9's could get over the division at a maximum speed of 45 with 4500 tons, maybe that was all that was necessary to meet the RR's standards after 1959.

I know there's a lot better information from others on this board.

Dave Stephenson



Re the N&W application, however, he is strictly
pencil pushy. His own SFH, p67, lists 432,200 WOD for the
Class A, which, divided by six, is actually less that the
2-8-8-4
 
How big a train the A could haul at 60 mph? 

What happened to N&W fast freights after dieselization?



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