Randy, Thanks for the calcs. What would the 80 inch wheel rpms be at 140 and 150 MPH?

Thanks, Ross Rowland

140 MPH would be 588.24 RPM so 9.8 revolutions per second.

150 MPH would be 630.25 RPM

Brian

PRR tested N&W J 610 between Crestline and Chicago in 1944. about one month after it was upgraded frm a wartime J-1 to full J specifications. No date or place i given but the report notes 610 had achieved 114 mph. This is the racetrack of the PRR and since it was a performance test, I'd guess that's all you can get from a J.

This is the same line where PRR fireman John Crosby wrote about T1 5536 with 15 standardweight cars from Van Wert to Ft. Wayne. They pegged the speedometer at 120. Here's the story:

https://cs.trains.com/trn/f/741/p/259651/2921432.aspx

Phil Mulligan

It’s not surprising at all that mile posts are off. Once established, the markers, if they still exist, don’t seem to be moved after a line has been re-surveyed due to changes. Their actual positions are usually noted on the charts in stations which are pretty accurate.

I took on a project to research and redraw an up to date track chart to scale for a tourist line. Quite a few of the MP locations weren’t exactly a mile apart though not terribly off. However, to complicate things, I can only assume that the last survey was done from both ends on one division which left a gap of almost a quarter mile on the old chart meaning those two adjacent MP locations were only about 3/4 of a mile apart. The error in placing the MPs was never fixed so for continuity the gap remains on the new chart notated to represent the original error so the MP locations are easier to find.

The long tangents across northern Ohio and Indiana could have allowed timing over a 5 or 6 mile section, which might have averaged out and reduced the impact of a misplaced mile post. It also would reduce the error in observing ones watch at the exact second in passing a MP. I don't know if this practice was common, or not.

I'd like to hear from some knowledgeable about the physics of this matter.

It's my understanding from some reading in a place I can't remember that the counterweights in drive wheels which are rotating can only balance the reciprocating forces of the rods at single or effectively at a limited speed, and exceeding that speed is what produces dynamic augment-so they are inherently unbalanced and the imbalance magnifies as a square of the speed.

If therefore, there's an imbalance at 100mph; it would be 44% greater at 120mph and 96% greater at 140mph.

Is this right, partially right or completely wrong?

And to quote Jeremy Iron's character from Margin Call; speak to me as you would a small child or a cocker spaniel. I didn't have the brains to get an engineering degree with the wholly inadequate work I used to breeze through high school, so kinematics and dynamics are out of my wheelhouse.

From the last Baltimore Division Employee Timetable I have (2008) for the Capital Sub (Baltimore to DC). "Note 4: The distance between BAA 6.0 and BAA 9.0 is 6,987 ft. MP 7 and 8 are not used". I think historically this is to account for the differences in mileage between the Cap and the Old Main Line, since this is the area around Relay, where the lines diverge. The OML does have Mile Posts 7 and 8.

It's my understanding the rotating mass from all the rods, including the connecting rod to the cylinders can be balanced. There is some cross balancing going on because of the quarter lead of each side of the engine.

Where things get complicated is the thrust from the cylinders through the connecting rod to the drivers also causes a cyclical imbalance. How much and which way to compensate for the thrust caused imbalance is headache inducing.

The J1 goes the route of little compensation for the thrust imbalance which lessens the rail pounding but has to keep the engine from waddling by laterally tying the engine to the tender's mass.

The T1 splits the thrusts over the divided drive hardware. I don't know if it uses the tender mass as well.

More Physics and Corrections welcome.

Brian

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Kelly, thanks. It'll take a while for me to understand but at least it's algebra, and not tensors or tesseracts...(spaniel barks appreciatively for fresh dog chow).

I can't find the discussion of the British 9F balancing, but the gist was that the balancing was done so that the 'hammer blow' was equal on both wheels in a driver pair. This alone was good for over 90mph with 58" coupled wheels.

For high speed, it is much more important to balance the revolving mass than the reciprocating mass. This is largely because at high speed/higy cyclic the time the yawing moment in one direction produces acceleration is comparatively small, and of course is nulled out by the following stroke. Much of the yaw couple is limited in effect when the engine has a long wheelbase; the N&W J augmented this with stiff lateral compensation on lead and trailing truck (which older heads may recall led to some trouble with "diesel-grade" short-radius incident curves in trackwork).

Glaze took all overbalance out of the main drivers except about 80lb. This was what he calculated as the vertical component of piston thrust at design speed (supe, PM me if this makes no sense to you). This would be adjusted -- slightly -- for other 4-8-4 types and trailing load.

Meanwhile, the very large tender and careful design of the radial buffer damps out the longitudinal surge due to imbalance, which is more of a 'problem' than nosing at high speeds. Bernard Langer at Westinghouse patented (in 1948) a gear-and-eccentric-weight system that balanced out the surge moments, and this would be particularly applicable to a T1 with Deem's geared conjugation of the two engines.

The Australians experimented with zero overbalance on a couple of classes highly dubious as high-speed locomotives, in order to reduce blow to an absolute minimum on light track.

The story of Bill Withuhn and T1 speed is a bit disappointing. He swallowed completely the Crosby 120mph story (not apparently realizing that the speedo on T1s only goes to 100mph) and also the Arnold Haas tale about 141.2mph (but with the S1, supposedly on the Trail Blazer in pre-Naperville speed-control resumption days, and the tale always ending in the "ICC" administering a "fine" -- let's just say that research in the ICC/FRA records produces no basis in a number of key respects). The anomalous Franklin results were most likely the result of high-speed slipping rather than actual road speed; it seems very unlikely to me that there wouldn't be at least one critical speed between ~120 and 145+ or a resonance that might be excited by a low rail joint or similar impulse. I do suspect that some of the Franklin and PRR reports of 'hard riding above 132mph" may have had some, shall we say, basis, but absent a controlled test with all four driver pairs instrumented, I don't see any assurance.

The failure of the J under test on PRR (at 114mph) wzs entirely a valve problem; the report being that the valve was actually heat-blued due to lubrication shortcoming. This was probably a combination of inadequate lube for the machinery speed and excessive superheat in the steam at that cyclic and cutoff -- it would certainly have been interesting to see what speed could have been reached with either type A or type B/B-2 poppets, but it wouldn't "prove" anything that PRR could use for itself in regular service with 70" drivers.

Thank you to both Mr. Anderson and Mr. Overmod for very educational posts.


Mr. Anderson, From reading your excellent tutorial twice I have come away with the impression that you feel that the PRR T-1 would have a reasonable chance ( based on its basic design features) of exceeding the current world steam locomotive speed of 127.5 mph .

Is that your opinion?

Thanks, Ross Rowland

I cant find the discussion either, but I did save the drawings from that discussion about the 9f.

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Here are some details on N&W 610 when tested on PRR in 1944. They are from an article in the N&W Historical Society magazine, The Arrow, Vol.24, no.4:

As a result of this information we can now identify three high speed runs made by 610 along with train sizes:

12/7/44 - 110 mph, train 71, The Admiral, westbound Crestline-Chicago, 15 cars
12/8/44 - 111 mph, train 57, Liberty Limited, westbound Crestline-Chicago, 11 cars
12/8/44 - 109 mph, train 28, Broadway Limited, eastbound Chicago-Crestline, 13
cars

610 was still set at 275 psi for these tests. Pressure was raised to 300 psi in 1945. This info is from N&W correspondence written during the test period, and is in the NWHS archives in Roanoke.