• E-units: SECOND intallment

  • Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.
Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.

Moderator: GOLDEN-ARM

  by Allen Hazen
The November 2008 issue of "Railfan and Railroad" -- the one with the second (E-3 to E-7) installment of Preston Cook's 3-part article on the development of the E-unit design. These articles, with their attention to the motivation for design changes, are fascinating, and ought to start many conversations.
The most visible change in design between the pre-WW-II E-6 and the post-war E-7 was the adoption of a less dramatic slope for the nose. (Is my memory being imaginative, or was there once a "Trains" article on the E-3-to-E-6 series entitled "Where are the noses of yesteryear?"?) I had always assumed that this was just a matter of standardization: life is easier if you only build one design of nose. (An "R&R" article on F-units by Preston Cook earlier this year told us that the cab/nose structure of later Fs was a module constructed in a different building and attached hole to the frame in the High Bay. It seems reasonable to suppose [BUT I DON"T HAVE DOCUMENTATION and would love to get confirmation from somebody] that the cab/nose modules of post-war Es and Fs were identical in construction.)

It turns out there was another reason for the change: decongestion of the engine room. By having a shorter nose it was possible to move the operating cab two or three feet forward. (Compare the E-3 and E-7 drawings in the article. The ladder to the cab door is entirely behind the center axle of the lead truck in the E-3, but entirely ahead of it in the E-7.) This gives a small but useful bit of extra length in which to spread out the mechanical clutter: desirable, since you want the stuff to be accessible for maintenance.

So, one might idly ask, why didn't they keep the original swept-back nose and just lengthen the carbody if they wanted more room? An obvious answer is that a longer locomotive body would also be heavier, and, as Cook remarks, "weight is not a friend in passenger service." (The E-unit story strongly suggests that locomotive design obeys a "law" familiar to students of aircraft or warship history: as a design evolves and is modified over its lifespan, weight tends to creep up. Carbody structure and -- this from the first installment -- the Blomberg A1A truck both had to be modified in later E-units to cope.)

BUT I WONDER if there is also a subtler reason for not wanting to change the length of the unit, having to do with track-train dynamics. Welded rail was not common when the E-unit was introduced. (I think the first American continuous welded rail was an experimental quarter mile somewhere on the Delaware and Hudson in... does someone remember what year?) The standard American jointed rail was built with 39-foot lengths of rail, and I think 39-foot axle spacings were considered undesrable: you don't want simultaneous KER-WHUMPs at both ends of the carbody. Now, the E-unit has 43 foot truck centers(*) and 7 foot (+ a bit) spacing between the axles in a truck: result is that when an axle in the front truck goes over one end of a 39 foot rail, each axle in the rear truck is at least 3 feet away from from the other end. If you increased the truck spacing to get more space in the engine room, however, you would approach double-ker-whump.

Final (obvious) remark: it's a very very nice article and anyone seriously interested in locomotive design and history should look for it!


(*) The Alco Dl-109, despite an overall length several feet greater than that of an E-unit, has the same 43 foot spacing of its truck centers. The post-war Alco PA is much shorter, and has 34 foot truck centers, but this with its within-truck axle spacing of over seven and a half feet still safely avoids 39 foot axle separations.
  by Allen Hazen
Just for fun, a bit about weight creepage: George Elwood's "Fallen Flags" site has some Pennsylvania Railroad locomotive diagrams. Their E-7A weighed 319,000 pounds, and their E-8A 335,000. Things gain weight.

And for those who like speculation about what might have been if the 244 engine and the Amplidyne control system had been more reliable, the PRR's weight for a PA-1 (with the same fuel capacity and a bit more boiler waterr than an E-7) was 312,000: on paper, and before the frequency of repair data started to come in, Alco's challenge to the E-unit looked impressive.
  by mxdata
Allen, part three is on the stands now here in the US. I suspect that you will enjoy the technical discussion of all the changes the Erie Lackawanna made to their E8's to try to make them acceptable freight locomotives.

I agree with you about ALCO. If the machinery in the PA-1 had been more reliable it could have seriously challenged EMD's position in the passenger locomotive business.