Steam & Excursion > SP's Cab Forward AC # Designations

I\'m intrested in how the SP used different AC #\'s for the 4-8-8-2\'s. For instance, SP 4274 is an AC11. What does \'AC\' designate, and the two digit # means ?

Thanks

Charlie

The original SP 2-8+8-2s were MCs, for Mallet Consolidation (and the 2-6+6-2s were MMs for...). When they started getting simple Mallets ca 1928 Baldwin had somehow convinced itself that simple Mallets weren\'t Mallets. I assume that\'s why the AC-4 and later were officially known as Articulated Consolidations.

Far as I know the AC-4 and AC-5 designations were just the successive batches that they ordered-- though there were differences of course.

timz wrote:

> The original SP 2-8+8-2s were MCs, for Mallet Consolidation
> (and the 2-6+6-2s were MMs for...).

MM stood for Mallet Mogul. Apparently SP didn\'t realize that all of these engines had a truck of some sort under the firebox.


When they started getting
> simple Mallets ca 1928 Baldwin had somehow convinced itself
> that simple Mallets weren\'t Mallets.

That\'s because "simple mallet" is an Oxymoron. A Mallet is, by definition, a compound engine.

I assume that\'s why the
> AC-4 and later were officially known as Articulated
> Consolidations.
>
> Far as I know the AC-4 and AC-5 designations were just the
> successive batches that they ordered-- though there were
> differences of course.

All were oil burning cab foreward designs, except the Lima built coal burning AC-9\'s.

What I don\'t know, is if all classes of SP steamers took the letter designation for their class from the Type Name, or if this was unique to the articulateds. How could 2-8-2\'s be "M" if the moguls were "M"? Were 2-10-2-s class "D" (for Decapod, again ignoring the truck under the firebox. Heaven forbid the SP would call them Santa Fe\'s.

SP 2-8-2s were Mk\'s, 2-10-2s were F\'s.

There is no official definition of a Mallet.

Charlie, now you are talking about my favorite engines. Class AC7 was the first group to have the semi-rounded cab front. After that the design was pretty standard. The AC10s were built in 1942; the AC11s in 1943 with no. 4274 being the last one. And class AC12 followed, right in the middle of the war. All this in Robert Church\'s fine book, CAB-FORWARD. I even rode the final trip of a cab-forward to Reno in 1957 behind 4274.

My understanding was that the "accepted" definition of a Mallet was that it was a compound, this being derived from the fact that the patent Anatole Mallet received was for compound articulated engines. Assuming that this is the case, a "simple mallet," as pointed out by MTMEngineer, would be an oxymoron.


timz wrote:

> SP 2-8-2s were Mk\'s, 2-10-2s were F\'s.
>
> There is no official definition of a Mallet.
>
> [%sig%]

I have a video of that run (in 1957) west to Reno on X4274 outbound, and #27 (section section) on the eastbound return. Great video. Anyone know the road # of the cab forward at Sacremento RR Meseum ?

The AC-12 in Sacramento is 4294, the last one built.
An easy spotting diference between AC-6 & later models is that AC-7 to AC-12 have disc drivers & the rectangular tender, while earlier ones have spoked drivers & that unique-looking "bathtub" tender with the rounded bottom.

Sacramento has the 4294.

Since Mallet\'s patent didn\'t include superheating (I assume), would you consider that the USRA 2-8+8-2s were not Mallets?

Not a perfect analogy, I\'ll grant you. But "simple Mallet" is a common-sense description of the engines that we would otherwise have to describe as "a four-cylinder simple engine articulated in the Mallet fashion". When they first started to appear in fleets (circa 1924-26) the Railway Age articles were headlined something like "Simple Mallets for the Chesapeake and Ohio" (and Great Northern, not sure about the DRGW). But for some unknown reason somebody objected to that usage and the trade press dropped it.

Ever since then, fans that like to think of themselves as purists have enjoyed looking down their noses at people that call simple engines Mallets. But it\'s plainly the sensible term-- more sensible than "simple articulated", anyway.

As a menber of the great mass of the "unwashed" we allas called the B&O EM1\'s mallets, just like all the railroaders ... articulated might have been in some folks vocabularies but around the roundhouse (?) they were "the mallets". You\'ll have to pardon us.

I think the bottom line was that any steam locomotive that was articulated was considered a "Mallet" even though it really wasn\'t under the true definition of the term. I assume that a compound engine that was articulated was a true "Mallet". But I could be wrong and it wouldn\'t be the first or the last time I was wrong.

steamjocky

At least two AC5s were rebuilt with the newer style cab as was AC3 # 4045

To add to the confusion, what would you consider the later engines (ie N&W Y6b\'s ect...) that could run either in Compound or Simple????
creeper

I\'m not sure exactly what you mean, creeper.

All* Mallets could be started simple, then switched to compound after the engine had run enough to supply LP steam to the front cylinders. Is this what you\'re referring to, or did N&W have something else?

-MTM Engineer.

*Disclaimer - Never say "all" on TO. Perhaps there were engines built without this feature, but I\'m not aware of them.

Maybe creeper is referring to the "booster" feature of the Y6b, the re-designed valve ("intercepting and reducing" valve?) that allowed some high-pressure steam to be admitted to the l.p. cylinders even while the engine was being worked in compound. I think all or most of the older Y5\'s and Y6\'s were re-built with this arrangement too. This shot of h.p. steam was a big help when shoving up the Blue Ridge grade east of Roanoke. As for the "Mallet" monicker, my impression is that most of the folk who worked with articulateds called them "Mallets", whether compound or simple.

The "MM" designation referred to earlier was actually somewhat accurate. the 2-6-6-2\'s that received that designation were, wheel arrangement-wise, a pair of Moguls back to back, thus the Mallet Mogul designation. The more questionable designation is the AC for Articulated Consolidation, since the 4-8-8-2 wheel arrangement was hardly a pair of Consolidations back to back.
Also, the old heads I worked with referred to anything with four cylinders as a Mallet, when recounting their years on them, and that included the AC9\'s. The SP engine crews generally referred to the F Class 2-10-2\'s as "Big Mikes" and the balance of the power was referred to in a general sense, by the road number series, i.e., 4300\'s, 4400\'s, etc.

steamjocky wrote:

> I think the bottom line was that any steam locomotive that
> was articulated was considered a "Mallet" even though it really
> wasn\'t under the true definition of the term. I assume that a
> compound engine that was articulated was a true "Mallet". But
> I could be wrong and it wouldn\'t be the first or the last time
> I was wrong.
>
> steamjocky
>
So, then should Fairlies, Shays, and Beyer-Garretts also be considered to be Mallets?

A. Mallet\'s patent was for a system of compounding. Lionel Weiner, in his definitive book "Articulated Locomotives", goes so far as to say that Mr. Mallet disapproved of the application of simple cylinders to his design.

My 1906 Locomotive Cyclopedia defines a Mallet as a compound engine. When the 1922 Locomotive Cyclopedia was published, they hedged a bit in their definition to also include the possibility of including simple engines in the definition. In the 1941 Locomotive Cyclopedia, they stated that simple articulateds were often called Mallets, but that they didn\'t truly meet the definition.

So, if SP, GN, B&O or anyone else wanted to call simple engines "Mallets", that\'s fine - after all, they\'re their engines and they could call them anything they wanted. But, the term "simple Mallet" remains an oxymoron, kinda like "military intelligence" <g>.

When you get right down to it, a Mallet is really a semi-articulated, since only the lead engine set swivels. A Beyer-Garratt is a true articulated because both engines pivot, giving the B-G much greater fexibility. Probably too late in the game to do much about the terminology, though.