UM20 prototype question

Curious about the internal structure of these. Did they utilize the conventional bridge-truss system that was commonplace in the 1950's and earlier for cab units, or were they early forerunners of cowl units where the locomotive frame was load bearing and the full width body just provided protection from the elements?

Good question; I don't know. None of the small number of pictures I have (in various sources) show diagonal truss members showing through the ventilation grills, which would be a good sign of "bridge-truss" construction, but they might not show.
An old (1970s) article on them in "Railroad Model Craftsman," written by Win Cuisinier (one of the best-informed writers on dieslelocomotive history!) just says that they closely resembled Alco FA/FB-2 in carbody design and equipment location, which isn't as explicit as we would want to give a definite answer to your question, but certainly doesn't suggest there was anything radically new about their carbody design, like a cowl arrangement.
GE's Australian licensee, Goninan, used a very similar carbody on a batch of locomotives (Class 43) for the NewSouth Wales Government Railway, in roughly the same period that NSWGR got conventional EMD (Class 42: six-axle F-7 variants) Alco (Class 44: "World" or Dl-500 type) cab units.(*)
Bottom line: I don't know for sure, but if I had to bet I'd go with truss design.
(*)There's a weight penalty with cowl and load-bearing frame design, which I doubt NSWGR would have been happy about, but this is also not conclusive, since they also got hood-type units.

I agree with Allen that the preponderance of evidence points to the GE experimental set that later became the UM20C model as being of conventional cab unit form with load-bearing sidewalls rather than being cowl units with all load-bearing done by the underframe. Cowl units were I think quite scarce at the time, and had GE opted for that form of construction, it would have been noteworthy and so likely to have been called out in the literature.

An interesting point is the form of construction that GE used for its shovel-nose cab units. In respect of the initial 1949 design for Argentina (LGB 621 class) it said:

“The platform is fabricated from plates and shapes. It is designed to get the static and buffing loads into the side sheets as near their source as possible. This permits using a minimum section and results in a substantial weight reduction. A housing suitable for A.A.R. draft gear is included at the front end of the platform. The rear end carries a draw-bar pocket and buffer assembly for connection between locomotive units.

“The cab sides and roof are fabricated from sheets and light, bent-up sections. These assemblies substitute for the conventional truss on the standard road Diesel, there¬by saving a large amount of weight.”

(from Railway Age, 1950 November 25, page 37ff)

This appears to have set the pattern for the following shovel-nose variants, and also the Philippines Manila Railroad streamlined cab units and the NSWGR 43 class. I recall reading somewhere that the NSWGR 43 had load-carrying side panels, but cannot retrace it right now. Of the Manila units it was said: “In appearance the ten passenger locomotives from preceding G.E. locomotives through the effect of the fluted side panels, a form of construction which adds to the strength of the sides.” (from Diesel Railway Traction 1956 October page 394ff)

The GE experimentals also had fluted side panels, which might have been used purely for cosmetic purposes but I think which were more likely used for increased strength, suggesting that it had the same form of construction as the concurrent GE export units.

Nevertheless, GE did use the truss form of carbody construction on some locomotives, such as the GN W-1 electrics. Pictures of one of these after its conversion to coal-burning turbine form by the UP (as #80B) clearly shows the truss structure over one section where the body panels have been replaced by mesh.


Cheers,

Pneudyne wrote: I recall reading somewhere that the NSWGR 43 had load-carrying side panels, but cannot retrace it right now.

I have since found it, in the book “Early Diesel and Electric Locomotives of the NSWGR” (1), on page 95, thus: “The 43s are the only locomotives in Australia with an integral body structure, that is, the side panels are welded to the frame.”

The 43s were ordered at the same time as a number of Clyde-GM cab units that became the 42 class. They followed a fleet of MLW-built Alco RS3 road-switchers (40 class), and in turn were followed by the first order for the Goodwin-Alco DL500 cab units (44 class). The 42s and 44s had truss-type sideframes.


Cheers,


(1) Mick Morahan; Early Diesel and Electric Locomotives of the NSWGR”; New South Wales Transport Museum, 1997; ISBN 0 90986 42 7.

GE also used load-carrying body side sheets for the Pennsy EL2b AC electric locomotives. This is from the descriptive article in Railway Gazette for 1952 April 18:

“In this design the body side sheets form side trusses carrying the whole load. There is a consequent reduction of about 40 percent. in the underframe material, against which there goes an increase of only 5 percent. in side sheet material.”

So, GE did use this form of construction in domestic as well as in export locomotives. That adds circumstantial evidence to the case that such construction was also used on the experimental diesel set.

Cheers,

Re: "So, GE did use this form of construction in domestic as well as in export locomotives. That adds circumstantial evidence to the case that such construction was also used on the experimental diesel set."
---Particularly since the E2b carbody has more than a passing resemblance to that of the diesel test units (both usually being described as "similar to an Alco FA"). GE was not, at the time of the diesel experimentals (released, i.i.r.c., in 1954), making many large locomotives for North American service: the market for main-line electrics had largely collapsed, and, famously, GE didn't try to enter the road-diesel market until about 1960. So probably the E2b were the most recent relevant GE designs: it's easy to imagine the designer thinking "Well, what worked well last time…"

(Next GE full-width carbody unit for North America was the New Haven EP-5, wasn't it? Do you have any details on its construction ready to hand?) (The punishment for coming up with good information is… you get asked more questions!)

Yes, well…..

I don’t have any hard information on the New Haven EP-5. But the in-build photograph on page 16 of Cunningham (1) does suggest that they did use the load-bearing side-panel form of construction.

Another candidate is the A-unit of the UP GTEL8500. Its sidewalls have that same smooth look. Not the B-unit, though, which in part at least followed the cowl form and from the photographic evidence had an apparently deeper underframe. From the description in Diesel Railway Traction for 1960 November:

“The superstructure follows the design commonly used in diesel-electric locomotives, although the section comprising the entire length of the turbines and generators is removable for maintenance purposes.”

That brings in the question – what about the GTEL4500 prototype and first 10 production units. The prototype might have predated GE’s adoption of load-bearing side-panels. And given the number of cutouts in those side panels, the regular truss form seems more likely.


Cheers,


(1) Joe Cunningham; New Haven EP-5 Jets; N.J. International, 1991; ISBN 0-934088-26-8