Vernon Smith wrote that the Alco PA’s were a few mph faster than the E’s. As for E’s, the UP had locomotive drawings with tables of tractive effort versus speed, where the top speed was 100mph.
One of the pieces of evidence for the ‘valve limited’ performance of the ATSF 3460 class invoked a top speed of 105mph being the highest ever recorded. That was less a documentation of ‘permissible speed’ than ‘possible speed’, I think.
There are all kinds of fan stories about weird high speeds with early diesels on ATSF – 120mph up to 150mph. These do not seem to be told by people who know how diesel-electrics work; the sort who say with a straight face that GG1 electrics have gone 156mph. But then I remember 108mph on 28" wheels testing the Electroliner, and the 90mph or greater speeds with 1-D-1 electrics the first day the Wilgus Grand Central Terminal electrification opened to traffic… and had wrecks…
bogie_engineer can explain this better than I can, and will know the specific numerical ratios associated with particular ‘speeds’ on different units, but gearing expressed as “speed” is NOT an indication of how fast a locomotive can go. It’s how fast it could theoretically be going before critical speed of traction-motor rotation is reached – where armature-winding swell and the risk of birdsnesting, for example, rear their heads. When you see a number like “92mph” or “117mph” or “120mph” it’s like an analogue of Kodak guide number for final-drive numerical ratio (the pinion and bull gear each needing to have an integral number of substantial strong teeth); wheel diameter; and traction-motor rotational speed limits.
Of course for marketing purposes saying your New Haven DL-109 pairs had ‘120mph gears’ was just ducky. The most egregious (mis)use of this I’ve seen was something that Louis M. Newton noted in Tale of a Turbine: one of Baldwin’s selling points for the TE-1 design is that it would cruise at 65mph on trains – something it would most emphatically NOT do in physical reality on N&W’s tracks. You now appreciate just why that was a scam…
An unfortunate consequence of Martin Blomberg’s design of the six-wheel A-1-A passenger truck was that only comparably small wheels could be shoehorned in (we have threads that covered this, but they may not have survived the truncation in transfer to discobot) and that would restrict achievable top speed a few mph with respect to a locomotive that could use 40" or larger wheels.
As you note, the gear ratio track speed limit is based on a safe rpm for the traction motor where there is little or no risk of the traction motor armature coils lifting out of their slots or the com bars rising. There also is a limit to speed based on the max generator voltage limit set in the control system.
It was our practice at EMD to test for stable running at 10% higher speed than the planned operating speed; FRA 49CFR 238.227 only requires testing at 5 mph above the maximum intended operating speed in a fully worn condition for equipment intended to operate above 110 mph. We had a worn wheel tread profile we would have turned onto the wheels that promoted truck hunting and would test up to a speed where hunting was initiated. During some HTCR truck development testing at TTC, we used their GP40-2 with high speed gearing to push one of the SD60MAC’s up to 96 mph to learn where the hunting threshold was.
Dave
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Another question for Dave: know anything about UP regearing SD40-2s before they started getting the 59:18 8000s? Think the below happened soon before the 8000s appeared.
Here’s the chart - almost all straight, so most likely no bothersome line changes.
No idea on that.
Going back more than a decade to when this issue, and the metaphor in the attached file, came up before, there was this post:
That of course still references the “80mph” gearing of the Fast Forties. I don’t think there is any credible way that 3129 would have had this gearing, so we are left to fall back on why that unit was coupled ahead of two SDP40Fs and in essence shoved down the grade, perhaps at low enough current that the windings were thought not to be critically heating. As noted, if the speed limit here were 79mph it implies there was no suitable automatic train control or cab signaling which would permit operation at 80mph in the first place… but there might be circumstances to explain it.
Back then Amtrak used the UP across Wyoming instead of DRGW. The UP engine would’ve been needed for cab signaling across Wyoming. I would guess it was convenient to add or remove a pilot engine at Denver.
Jeff
The Santa Fe dropped its limit throughout to 90mph in the late 50s. It’s never gone back up. If interested you may check this link for dozens of ATSF employee timetables through the 1980s.
https://wx4.org/to/foam/maps/and_timetables7.html
For post year 2000 you can look at BNSF timetables. Sorry only 90mph here too.
https://fobnr.org/bnsf-timetables-phase-4/
Wonderful article in an early issue of Classic Trains describing exactly how a Super C was operated at speeds up to 90mph practically. I did not appreciate it when I read it, but came to realize its value later…
When the North Shore tested the Electroliners at 108 they found that the trains beat the gates down at the crossings so management promptly disconnected the field shunts and that limited them to 75. Sure enough some wise guys secretly reconnected the shunts when they wanted to go faster, so when management found out they physically permanently removed the shunts and destroyed them. This was according to an article I got in my Con-Cor Electroliner HO model.
The Brill Bullets in Philly they had the same problem. Same solution. Max went from 90+ to 70 per CERA Bulletin 126.
Boys will be boys. Girls too!
If it can go over a 100, it will sooner or later, until Mom or Dad takes the keys away.
Whistling the Beach Boys to myself.
And I got my father’s T-Bird to learn to drive on. You know how kids are banging stuff up as they learn… Thing was, it was a four-seat convertible that would go over 130mph. Few made a new car by 1974 that would do that. Factory double-pumper with four perfectly equal venturis…
Story I heard was that at the completion of the test run, the train went straight to the shop where the brackets and connections were torched off. Almost not a word was spoken…
“The UP engine would’ve been needed for cab signaling across Wyoming”
Good bet the SDP40Fs came with all the stuff they needed for the RRs they ran on. In any case, they ordinarily ran unaccompanied on UP for the first few years at least.
(Until at least 1972, UP allowed SP and WP units to lead freights east across Wyoming.)
Going fom pictures of run thru trains on UP, up to sometime in the early mid 1970s, foreign, non cab signalled engines were allowed to lead. I’m wondering if the change to stricter requirements came with the establishment of the FRA.
Jeff
That’s somewhat of a soft limit. With series motors, when the generator voltage reaches the limiting value, any increase in speed will require a reduction in current (hence power) and the tractive effort will drop off even faster. Using field shunts or taps will increase the speed where full power can be delivered to the motors, but there’s a limit on how much shunting can be applied before causing problems with commutation.
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This is very true. Mileposts are inaccurate at times. I’ve seen mileposts over 7000 feet and under 3000. I’ll dig to remember where and if I find them I’ll post.
And it’s easy to misread a time too.
In the Hiawatha runs I posted a couple weeks ago one of the runs must have had a bad time as the speed before it was 137 and 78 after. So I tossed out both and found the average over both segments to be 103. Consistent with the rest of the times. So I adjusted both to match 103.
Erik I know that’s true for level ground. Do you know if a falling grade will still push it faster or will the greater over speed further increase back emf and resist it. Even if the power is shut off?
In other words a car in gear on a steep downgrade the engine will resist the speed while in neutral it won’t. In a series motor does it matter if the power is on or off?
Amtrak did have multi-RR cab signal systems installed.
