Juniatha
[Haas] also wrote a Niagara would accelerate faster from 80 to 100 mph than from 60 to 80 - which would only be possible if the mean tractive effort would be larger in the higher speeds - which by itself is virtually impossible.
This is not necessarily complete tripe; it is possible that, using the 'reservoir' of supercritical water and excess available superheat at high draft level, there would be 'enough steam' to produce the necessary acceleration. Not particularly cost-effectively, and with no guarantee that the locomotive would hold speed (or continue acceleration) beyond a few seconds or minutes, but the higher cyclic does translate into greater cylinder horsepower up to the point that the valves and gear cannot cleanly admit and release the steam ... and assuming the running gear can transmit the thrust without problem, which I think is quite a different matter...
Do I really think that acceleration all the way from "80 to 100" would be faster than "60 to 80"? Not really... but I'd want to see proof before calling him even more of a fibber... 
The Niagaras had comparatively very small cylinder volume for given boiler pressure (in relation to both their adhesion mass and their steaming capacity, that's why their highest indicated output was only reached around 75mph at 52% cut off - a very inefficient, long c/o. I think Paul Kiefer didn't want to take risks on too high a piston force and / or to long a piston travel.[/quote]
IIRC that Kiefer originally specified 290psi for this design, and to be honest I would think the old story about the Super Hudson design providing too much 'thrust or kick' and bending rods would be far more applicable to the Niagara. It might be interesting to run comparative numbers for the Niagaras at original vs. stepped-down pressure to assess what the 'right' cylinder dimensions for 265psi would have been.
With a cylinder volume half ways more to the example set by the N&W J class the Niagara's ihp could have surpassed the 7000-mark easily and on the same coal consumption ... however maybe Paul Kiefer was wise not to overdo things - today substantially larger piston forces would be no problem with superior materials.[/quote]
eBut the issues with Niagaras did not involve "greater peak horsepower" -- the water-rate considerations even on a railroad with frequent track pans would have become significant with the advent of proper water treatment for modern boiler steels -- and in fact if you look at the assumptions behind the detail design of the NYC 5550 (and inherently in the April '45 spec for the C1a) you will see this very clearly. Reading between the lines, I suspect there were the same kinds of failure that N&W was seeing with the extended #4 driver-pair pins on the original lightweight J rods; the Niagara design was somewhat more susceptible to priming even with the careful steam-separation design, and the result on the very lightweight Timken construction could be dramatic.
All those questions of 'how fast did she go' and 'how fast did she really go at maximum' and 'if we allow the engine to throw rods way ahead in the event - what speed at maximax could at-all ever have been reached for just a moment' are fine and exiting to those who do not take a closer look at what it takes beyond boiler power and ability of cylinders to operate the filling and exhausting in a half ways civilized manner - as is when the valve gear will work orderly and keep together by that.
eN&W and PRR, of course, found a point of failure that came up 'quicker' than valve-gear problems: insufficient valve lubrication (or dimensional clearances) at superheat and machinery speeds in excess of 'design'. While some N&W valve-gear was notorious for, 'unraveling' at times, as Ed King memorably put it, that was not a factor in the infamous test failure on PRR either by the noted results or later discussion of the testing by Cover et al. as preserved at the Hagley.
Mind that with a 20% over-revving, forces reach 144% of the design maximum. Who will tell me it can stand that for any longer than a few minutes?
Especially if Chapelon was correct in his assessment of 'routine' lateral bending in the Timken narrow-section lightweight rods.
Of course, that presumes the engine can actually be over-revved continuously, rather than (as was clear to me) repeatedly high-speed slipped without proper notice -- as in the case of the "130mph and higher" operation reported by 'Franklin engineers' to Vernon Smith in the '40s. The combination of inertial and shock forces on lightweight rods in high-speed slipping is, if anything, far higher in the deleterious senses than steady-state high speed would be, and probably makes your point even more compelling.
If we take instead a look at the permanent road bed then we must ask where in hell should an engine have even reached such speeds before outrightly derailing? Name me the 1930s 1940s track if you can? I bet you there was none - not with the universal simple nailed rails and that sloppy joined rails and that minimum of 'dirt' embankment.[/quote]
eYou're leaving out the enormous amount of maintenance that was used by railroads like the Pennsylvania or NYC to keep a jointed-rail mainline in proper shape. Something similar was involved on railroads like C&NW and Milwaukee in the early Thirties to get a railroad of almost primitive civil construction by modern standards to take 100mph operation with motor trains and then with steam locomotives. There are plenty of references on how to do this that refute a cavalier description involving 'nailed' rails and 'dirt embankment'. NYC as late as 1966 was able to observe 183mph running nearly-unmodified RDC trucks on what I recall to be jointed rail -- that in itself is not a pure reason to discredit a certain amount of high-speed operation, at least one-time or for 'special' purposes.
There is no question however that better use of LWR and proper fixation systems would be appropriate, if not necessary, for any sustained running with reciprocating steam much above the ~100mph maximum practically achieved through the end of 'commercial' large high-speed steam operation in the United States. And that even at the peak of the section-gang era on PRR, the absolute track quality was any better than would permit "safe" operation at indicated track speed -- as you note, 80 to 85 max.
Now, on the other hand, there are some interesting things that come up with regard to actual track integrity. In addition to the Haas argument, which I believe was supposed to have been reported in the German literature as 1947, conveniently just ahead of the ICC order (which didn't take effect until 1950, but that point might be lost on someone not familiar with US government practice), there was a story in the magazine Popular Mechanics in which someone supposedly involved with running 6100 claimed she had run 138mph. We could have fun discussing the various mechanical details that might or might not have allowed such operation ... but instead, look at the Google Earth or historic-aerials view of the particular location where the PM 'feat' was supposed to occur. This goes right through the middle of a town with streets and buildings closely encroaching on the right-of-way, and directly to the west of town there is a railroad crossing at grade. Personally I can't imagine operating a reciprocating locomotive at high speed across jointed diamonds and untuned paved grade crossings, even with a proper modern suspension...
And then there are the suspension and riding characteristics of the actual consists PRR would have run behind a locomotive at such a speed. There are a number of reports -- whether anecdotal or 'doctored' I can't say, but I find them probable -- that the great majority of contemporary PRR equipment was encountering considerable, shall we say, nonlinear suspension and guiding behavior at speeds as low as 110 to 115mph; one of these stories claims the ride on a T1 was considerably better than in 'the business cars behind' which remains to be properly established with replica 5550 modeling and testing, but as far as the rolling stock goes is, I think, capable of establishment with far less rigorous proof.
The idea that "142 and a fraction" mph is just a smidge higher than "138" is even more amusing, although to the kind of people who think automotive practice -- like 120mph speedometers -- characterizes railroad design, it might seem less unlikely.
Some years ago I saw an advertising film by the Pennsylvania, it was to show how soft, caring and smooth the passengers travel on the PRR high speed mainline track. Now, I must say, they were being bounced around quite a bit and swayed sideways - and at what speed? watching the outside trees and houses go by it was some 80, 85 - at best! All in all it was more like on the - sorry - PKP, the Polish state railway when in the 1990s they had been cought by the fresh wind of change and had put on some speed, rising from 100 km/h mostly to more 120 km/h stretches, just like that, track upgrading only following year by year. That said, I had also witnessed an upgraded electric line travelling from Bydgosz to Warzawa: that was 100 mph on all-welded, straight and billard table level track, the neighboring rails were dashing by without showing any flares or buckles in the flow. Had the Pennsy had this sort of track I would consider 110 - 120 mph for some T1 rides - but still not like 'more often than not' or as last run of a worn down neglected engine![/quote]
A great deal of PRR practice fell apart very quickly during (and after) WWII -- see if you can find the postwar ad that goes into their track-structure cross-section and essentially whines that the Government needs to help them rebuild after their colossal effort to help win the war... etc. In any case my personal, and essentially unjustified, opinion is that PRR made a great more out of high speed running than their actual plant ever really permitted except in a few, fundamentally virtually unimportant, sections. Some of the discussions of doubleheaded K4s up against their practical speed limit (of about 92mph) mention the most alarming loss of compliance or guiding integrity on curves -- without discussion of what that kind of shock might do very quickly to jointed or spiked rail or track geometry. But I was not there to complain.
Let's ignore a number of points standing against these high speed claims and look just at the fact that over-revving would have soon worn down the cam surfaces if no more of the poppet valve gear.[/quote]
eThis is not a major factor for the PRR T1, at any rate, which used an OC gear with lower travel at shorter cutoff, and valves with comparatively low inertia. Even the crude increase in spring pressure to debounce the valves would not have radically increased cam-lobe wear as the springs were progressively wound and lobe engagement would not have been under high pressure (i.e. not desmodromic) close to valve cutoff. The cam-lobe wear in the original laterally-shifting design of the late Forties was more associated with line contact at 'common' settings between the complex contour and the spherical followers -- but this was less a 'performance' issue than a flexibility-in-service one. (We could argue whether modern materials and surfacing techniques can partly or wholly overcome some of these issues -- but other considerations are I think much more significant)
Interestingly, the problems with the T1 maintenance do not appear to have been either in the 'inconveniently-located' gearboxes or in the actual oscillating-cam and follower mechanism, but in the little valve gear pieces that (erroneously, in my opinion) control the motion. SHM makes sense to drive long-lap, long-travel valves, but simply doesn't apply to the 'proper' motion of poppet valves admitting steam.
It is my uncharitable assessment that there was more than a little 'tomfoolery' in Kirchhof et al's claims for the original Franklin System as being something that could be effectively driven in conversion by conventional valve gear ... but some of that remains to be established in actual modeling and testing.
At this point the discussion becomes highly interesting in a number of significant effects -- but I have to go attend to other business. I'll take up some of the other points in a few hours, God willing.