And one might say that sometimes the designers were setting their weight aspirations too low....
Whilst “aspirational” does seem to be the best fit for the 417 000 lb number, another possibility is that 417 000 lb was the base weight for the “bare bones” version with FB-3 trucks (assumed to be lighter than the GTEL trucks) and without dynamic brakes or any other extras. Keekley’s “417,000+ lb” number might have been intended to convey that idea.
To test that notion further, I looked firstly at the FM Train Master case, using the weights given by Sweetland (1). I chose the TM because it appears to have been the first American domestic market C-C unit that was designed to be approximately equivalent to 1½ regular B-B freight units in the 1500 to 1600 hp range, both in terms of power and adhesive weight, rather than simply a similarly powered six-motor version of a regular four-motor unit. The U50C could be thought of as having been a later development along the same vector started by the TM.
The “bare bones” TM weighed in at 343 000 lb, that number increasing to 366 000 lb for the fully-equipped version. Ballast could take that to 375 000 lb, and overballasting, as done for the VGN examples, to 396 600 lb. Against that, a spread for the U50C ranging from 417 000 to 443 000 lb seems not to have been impossible, although unlike the TM, I don’t think that the U50C had a train heating boiler option to add significant weight, so that works against the idea somewhat.
For a moment accepting that the 417 000 lb “bare bones” weight was realizable, would UP have wanted or needed a heavier version? Well, the GTEL8500 put 8500 hp on 850 000 lb, or 4250 hp on 425 000lb for each half. So with 5000 hp, the UP may have been reluctant to drop below the 425 000 lb number, and may even have been looking for an increase to better cope with the increased power. No doubt the U50C had a more sophisticated wheelslip control system, but then it had an 8-notch throttle as compared with the 20 notches for the GTEL, and so the starting tractive effort increments were larger. (I don’t know if the U50C had the humping control, which GE also offered as a smoother way to control starting and low speed tractive effort.)
If one views the U50C as being three-quarters of a DDA40X, which weighed 545 000 lb (according to Cockle), then the U50C target weight would have been just 409 000lb. But the DDA40X trucks were probably of the high-adhesion type, whereas those GTEL trucks on the U50C definitely were not. Conservatively one might impute an effective 10% adhesion weight advantage for high-adhesion trucks, which would in turn suggest 449 000 lb for the U50C.
So playing with the numbers doesn’t exactly move the alternative theory into the implausible class. But the “weight” of history still points to underestimation during the design process as the primary suspect.
I also looked at the Alco DH643 case. This was primarily an experiment with hydraulic transmission, and was intended to be proximate to the Krauss-Maffei ML4000. But if one neglects the transmission aspect, the DH643 may be seen as an intermediate step along the same C-C unit vector that connects the TM to the U50C. Strapac (2) gives the original weight estimate for the DH643 as 373 000 lb. There is no commentary about weight gain between inception and realization, but evidently that did happen. In his tabulation of the SP diesel-hydraulic fleet, Strapac quotes the “invoice weight” for each of the Alco DH643s as 400 900 lb. Steinbrenner, in his Alco history, “mentioned 200 (short) tons, which is in reasonable agreement. Railway Gazette (1964 October 16) gave 174 long tons, roundly 390 000 lb. And Keller gave 180 tonnes, roundly 396 000 lb. So as with the U50C, we’re seeing a range of weights quoted, and with a spread of about the same magnitude. But in the DH643 case, it is known that the “low” number was an estimate, not an actual, and putting the DH643 weights alongside the U50Cweights, does suggest that the U50C ”low” number could well have been an estimate.
Returning to, or rather getting closer to the FB-3 truck itself, and I think germane to the topic, is GE’s pathway to the FB-3 truck. A quick initial look comes up with the following.
The starting point for GE domestic-market C-trucks – at least in the post-WWII era - seems to have been the New Haven EP-5 rectifier electric locomotive. This had an inside-equalized, single-swing bolster trimount type truck, evidently designed for good riding and tracking at high speeds. As well as the two (per side) customary between-the-axles primary coil springsets, it also had outer, stirrup-mounted springsets. I am not sure when such were first used, but they seem to be strongly associated with the Fairbanks-Morse Train Master, which had rigid-bolster trimount trucks. Another feature of the EP-5 trucks was that the spring pair between the centre and outer axles were separated to allow room for the bolster elliptic springs between the coil springs.
Next was the Virginian E33 electric locomotive. One imagines that in deference to its lower speed freight haulage role, it had simpler outside-equalized rigid bolster trimount trucks, with the usual two primary springsets per side. VGN itself may have seen swing-bolster trucks as an unneeded luxury for its operations. For example, its preceding EL-2B motor-generator electric locomotives had rigid-bolster B-trucks, whereas for example GE’s more-or-less contemporary GTEL prototype had swing-bolster B-trucks, also with span-bolsters.
Then the UP GTEL8500 was different again. It had inside-equalized trucks, with four primary springsets per side, and rubber-sprung floating double bolsters. By this time GE had adopted floating bolster trucks, in both B and C forms, and outside-equalized, for its standard export road locomotives. So one assumes that it wanted to try the rubber-sprung floating bolster in domestic service, as well. And although the GTEL8500 was a freight locomotive, with a 65 mile/h top speed, either GE or the UP, or both, had decided that it lateral motion rather than rigid-bolster trucks were preferable, perhaps in consideration of the fact that it would do quite a bit of relatively fast running. The preceding GTEL4500s had had swing-bolster B-trucks, and UP’s history had included paying more attention than average to steam locomotive springing and lateral control systems.
It might be noted that for its export road locomotive designs with C trucks, GE had started with the rigid-bolster then had moved through swing motion to the floating bolster design, in all cases with the pivot more-or-less central.
The Pennsylvania E44 followed the Virginian E33 in using rigid-bolster trimount trucks. On the one hand that looked logical, given that it was a freight locomotive. But on the other hand, Pennsy’s freight experimentals, the E2b, E3b and E3c had all used swing-bolster trucks. In particular, the E3c had single-bolster trimount trucks similar in principle, although not in detail, to the EP-5 trucks. And the Pennsy had had a history of paying careful attention to the tracking and riding qualities of its electric locomotives. In the case of the E44, it might have been that the champions of mechanical simplicity won out over those who were more concerned about riding and tracking performance.
The choice of the rigid-bolster trimount type for the U25C would seem to have been made on the same basis, that it was essentially a heavy freight locomotive, and that simplicity was paramount.
The standard export models were equipped with floating bolster, outside-equalized C-trucks through the 1960s, but the non-equalized form had made its appearance on special export variants from circa 1963. So all of the elements were in place for a domestic C-truck with floating bolster and non-equalized, and with its pivot essentially central. One has the impression that GE was never a highly enthusiastic user of the trimount form.
(1) “Train Master”; Diesel Era with David R. Sweetland; Withers, 1997; ISBN 1-881411-13-3.
(2) “Southern Pacific Historic Diesels Volume 2 Diesel-Hydraulic Locomotives”; Joseph A. Strapac; Shade Tree Books, 1993; ISBN 0-930742-15-X.
(3) “High Power Diesel-Hydraulics”; Rolf Keller (of Voith); Institution of Locomotive Engineers Paper No. 687. 1967 March.