A and AE

Thu Feb 12 14:12:59 EST 2015

Eric: I believe that you meant the VGN AG not the AE. The AG was the 2-6-6-6 and the AE was the 2-10-10-2. Two very different machines. Harold Davenport   

On Wednesday, February 11, 2015 9:33 PM, NW Modeling List <nw-modeling-list at nwhs.org> wrote:

I have been ruminating on a comment made in this forum several weeks ago to the effect that the N&W A was a superior engine to the VGN AE or C&O H-8, because the A produced more tractive effort with far less weight (and implied stress) on the track, despite the fact that it was an 8 year older design.   

The claim of higher tractive effort for the A surprised me, but is theoretically accurate based on boiler pressure (300 psi for the A vs 260 for the AE and H-8), cylinder bore (24” for the A vs 22.5 for the AE and H-8), stroke (30” for the A vs 33” for the AE and H-8), and driver diameters (70” for the A vs 67” for the AE and H-8).  The net result is a theoretical tractive effort of 114,000 pounds for the A vs 110,000 for the AE and H-8.  Despite the larger drivers and shorter stroke, the A achieves its higher theoretical tractive effort through its larger cylinder bore and higher boiler pressure. 

But an (equally theoretical) analysis indicates that the A’s factor of adhesion was 3.44 (indicating a propensity to slip pretty easily), whereas the AE was 4.49 (indicating a VERY “planted” locomotive), and if the weight rumors of the H-8 were true, its (theoretical) factor of adhesion would have been a bit higher than even the AE. 

Both classes were designed to run at 70mph, but the design philosophies to do so were different.  The longer AE stroke and smaller diameters would have resulted in ~15% higher piston speed at any given speed, but the same dimensional differences would have resulted in ~15% lower static load on the main and side rods for a given tractive effort.  This and the ~18% smaller piston mass would have allowed ligher main and side rod mass and potentially easier dynamic balancing—thereby allowing the AE and H-8 to achieve the 70 mph design speed, even with 4.5% higher driver rpm than the A. 

I think it’s undisputed that the AE / H-8 design produced nearly 40% more horsepower than the A. 

So here are the questions I’m driving to:   

Did the A slip on starting?  Were the AE and H-8 notoriously sure-footed on starting?  Could either type start markedly heavier trains than the other under similar consitions? 

Could the A run any train at 50mph that it could start? 

Could the AG start any train it could run at 50mph? 

Did N&W and VGN operate the A and the AE over similar profiles at any given time (e.g., Narrows to Roanoke, or Roanoke to Norfolk)?  Did they use coal of approximately the same grade on these runs?  Did one deliver more ton-miles per hour, over similar profiles, with approximately equivalent quality coal? 

-Eric Bott   
________________________________________
NW-Modeling-List at nwhs.org
To change your subscription go to
http://list.nwhs.org/mailman/options/nw-modeling-list
Browse the NW-Modeling-List archives at
http://list.nwhs.org/pipermail/nw-modeling-list/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://pairlist6.pair.net/pipermail/nw-modeling-list/attachments/20150212/0f171a62/attachment-0001.html>