150-Mile-Per-Hour Steam

[tomikawaTT]

I do the same thing, Quentin.  I could fit my rather small frame between the outer rim surfaces of a Challenger's drivers quite easily....diameter-wise I mean.  I'm not thin enough to actually squeeze between two drivers.

If you have ever found videos on youtube of UP 844, with its 80" drivers, and then found one with it doubling Challenger 3985 at track speed, you can see a marked difference between the two (oops, three) sets of drivers.  The Northern-type prances along in a stately manner while poor ol' 3985 churns like a mud-racer.

-Crandell

Santa Fe had one class of Hudsons with 84 inch drivers, IIRC.  And then there were NYC 999's original 86 inchers (no longer installed, unfortunately.)  Imagine NYC 999 (4-4-0) doubleheaded with a contemporary 56 inch drivered consolidation.  The mind boggles!

And then there were the Pearson Singles - 4-2-4T, 96 inch flangeless drivers, designed to run on Brunel gauge (which allowed plenty of room for the boiler between the drivers.)  They lasted for a long time, even though their tractive effort was about the same as that of a 4-wheel-drive SUV.

Chuck 

[timz]

Counterbalancing,

Let's say they're designing the engine for 100 mph-- then word comes down from the top: revise the design so it's good for 140 mph. How will they change the counterbalance?

cross-balancing

A 100-mph engine wouldn't be cross-balanced?

and the stiffness of the lead and trailing truck centering devices (which help to control the effects of dynamic augment) - for openers.

With the 140-mph engine being stiffer than the 100-mph engine, right? Is there any disadvantage to the increased stiffness?

[timz]

As for, "Who said the J was designed for 140MPH?"  The people who designed and built them.

You must have read my mind. An N&W publication said the J was designed for 140 mph?

[feltonhill]

Going by memory here (I'll try to find the source later), N&W qualified its statement by saying something like the counterbalancing was designed so that rotational speeds of 140 mph could be achieved before wheel lift occurred.  I don't believe that's the same thing as being able to run at 140 mph, which implies transmission of significant power rather than just rpm.  The exact wording N&W used is important and I'm not quoting it accurately.  i'm fairly sure they did not make a blanket statement that the J was designed for 140 mph. 

[feltonhill]

This is from a feature article in Railway Mechanical Engineer, June 1945.  The N&W Class J running gear is discussed in detail -  

"The weight of the reciprocating parts of these locomotives is 1,547 lb., of which 35.6% is balanced.  The weight of the revolving parts is 2,747 lb.  The overbalance is 175 lb. for the front, intermediate and back wheels and for the main wheels, 25 lb.  The dynamic augment at 70 mph is 9,016 lb for the front, intermediate and back wheels and 1,284 lb at the main wheel.  A speed of 140 mph would be required in order that the dynamic augment equal the static wheel load of 36,000 lb.  The maximum sustained speed of the Class J locomotives handling 14 cars (1,000 tons) on level tangent track is 100 mph." 

I don't believe this is the same thing as being designed to run at 140 mph.   

The test runs of Class J 610 on PRR in 1944 were in regular passenger service and a maximum of 111 mph on one of the trains was documented by two Asst. RFE's in a memo to their boss, J. A. Warren.  See Apr-June 2008 issue of N&WHS magazine, The Arrow, for  details.