The Other Way Round - or: SP class AC-12 cab-forward

[NGT6 1315]

Well, as announced earlier this month I would now like to post some photos of what I think is among the most intriguing steam engines - both within the United States and around the globe - ever to be built .

 

As many of you will most likely know, back in the early 20th century train operations on the Southern Pacific's network were severely hampered by the fact that significant lengths of their line through the Sierra Nevada had to be sheltered by snow sheds or built in tunnels due to the severe winter weather often found in the region, which would often bring feet upon feet of snow and a significant risk of avalanches. This, in turn, caused two major problems for those steam engines in use at that time. Obviously, lots of smoke and ash would collect under said snow sheds and inside the tunnels, often eliminating visibility for the engine crews, and also exposing them to hazardous gases - thus effectively eliminating the advantages the high-powered engines which began to appear in this period did offer. In some cases the sheer power of the exhaust blast even reportedly blew off the roof panels from the snow sheds.

 

As a stop-gap measure, SP began equipping their engine crews with oxygen breathing devices, as introduced in the aviation world at that time. But these, of course, could not eliminate the problem of lacking visibility. Therefore, some engine crews simply arranged for their engines to be turned before entering the route in question, running with the tender in front. Naturally, this was not an ideal solution either as the stabilizing effect of the tender can only apply when behind the engine, and as the engineer then found himself on the left side when looking in the direction of travel - thus risking not seeing signals and other important wayside items in time.

 

After receiving their class MC-1 2-8-8-2 engines in the traditional form with the cab at the rear of the boiler, the SP engineering department then specified a cab-forward layout for the follow-up MC-2 type which was first built in 1910. As there was no practical way of burning coal on these engines - in later years the Deutsche Reichsbahn would struggle with severe problems on their 4-6-4 express cab-forward engine 05 003, which used coal dust but where the fuel pipes into the firebox would often be clogged by said dust - they were designed to burn bunker oil which could be pumped into the firebox with relative ease. But anyway: The cab-forward design as such proved to be a big success, and a total of 256 engines spread across 17 types were built until 1944. Those cab-forwards which had originally been built as Mallet compounds (classes MC-1, -2, -4, -6, MM-2 and AM-2) were converted into simple expansion engines by about 1930, having proven themselves to be too slow in the meantime.

 

The last of the SP cab-forwards was the class AC-12 4-8-8-2, with twenty engines built between October 1943 and March 1944. All cab-forwards were retired between 1955 and 1958, and only the very last engine - number 4294 - was kept as a monument which is now exhibited at the California State Railroad Museum. All SP cab-forwards were built by the Baldwin Locomotive Works in Pennsylvania.

 

But now on to the photos .

 

 

 

Intermountain recently launched a new production run of this amazing model, with several road numbers to choose from. Mine is 4275, the model carrying the reference number 59002. The model is also available with DCC sound.

 

 

 

While earlier cab-forwards had flat cab fronts, the AC-11 and -12 had more rounded fronts, which I think look quite nice actually. Also note the air horn in the middle of the front above the coupler and the number boards above the windshields. In the beginning the engine crews did have reservations about crash safety on the cab-forwards. However, to my knowledge there never were any serious collisions with any of these engines.

 

 

 

 

A closer look at the forward half of the engine with the cab, firebox and first set of drivers. Lots of separately added details such as pipes and handrails there - this is a model to be handled with care! Looking closely, you will be able to see how the gauges inside the cab are actually highlighted.

 

 

 

The rear half of the engine. Although it would not really have been necessary on this kind of engine - at least not for purposes of higher visibility - SP painted the smokebox silver. Old habits die hard, I guess. The platform between the smokebox and the tender was known as the "monkey deck" and often used by the so-called hoboes to travel across the country. However, I read that many of these were scalded or asphyxiated inside snow sheds and tunnels by smoke, fumes, boiling water and mud exhausted from the chimney. That does not exactly conjure a pretty image...

 

 

And finally the tender. On the real thing the oil tank was pressurized by air to further facilitate fuel transfer into the firebox.

 

 

As you could see from the photos, this is an extremely well done and finely detailed model. However, I also read it does require very carefully laid tracks and will easily derail otherwise. As I do not have any layout I cannot make any tests of my own, though.

 

 

As usually, I hope you could make some use of this information .

[Oldddudders]

 

As you could see from the photos, this is an extremely well done and finely detailed model. However, I also read it does require very carefully laid tracks and will easily derail otherwise. As I do not have any layout I cannot make any tests of my own, though.

It does look lovely! My own experience of Mallet-type locos is that they run really well! My rather unintelligent tracklaying and tight clearances mean that some of my longer-wheelbase locos can derail - but they tend to be the 2-10-2s and the 4-8-4. My 2-8-8-2 and 4-6-6-4 seem to go more or less anywhere. Incidentally, the very latest batch from Intermountain have been panned by dealers - they run badly and slowly, and appear to be poorly assembled, relying on the purchaser to do wholesale lubrication to compensate. The wiring also appears to have been done by a birdsnest freak. Tony's Train Exchange in Vermont have sent their whole batch back! I sincerely hope your model is from a previous, successful run, of which I know there have been several!

[pH]

This, in turn, caused two major problems for those steam engines in use at that time. Obviously, lots of smoke and ash would collect under said snow sheds and inside the tunnels, often eliminating visibility for the engine crews, and also exposing them to hazardous gases - thus effectively eliminating the advantages the high-powered engines which began to appear in this period did offer. In some cases the sheer power of the exhaust blast even reportedly blew off the roof panels from the snow sheds.

Apart from the hazardous gases, heat was also a problem in the tunnels. Northern Pacific did some tests in their tunnels on Stampede Pass in Washington State in the 1930s, using one of their biggest steam engines of the time. In one test, on entering a tunnel, the cab temperature went from 49 Fahrenheit to 130 Fahrenheit in 90 seconds ! Later, following the principle of the SP cab-forwards, they tried running the engine backwards. Cab temperature went from 80 to only 92 degress, but the temperature in the dynamometer car, behind the engine, went up to 140! Based on these tests, NP drew up designs for their own cab-forwards, but these were never built. Instead, they converted to diesels (which have their own problems with tunnels - see the tunnel motors).

[NGT6 1315]

Incidentally, the very latest batch from Intermountain have been panned by dealers - they run badly and slowly, and appear to be poorly assembled, relying on the purchaser to do wholesale lubrication to compensate. The wiring also appears to have been done by a birdsnest freak. Tony's Train Exchange in Vermont have sent their whole batch back! I sincerely hope your model is from a previous, successful run, of which I know there have been several!

 

 

Thanks for the heads-up, Ian - does this apply to the AC-12 specifically or to other IM models as well? And, do you know when the botched batch was shipped to the dealers? Mine received his latest load only in early December.

 

Right now this is not much of an issue for me anyway as I have no place to run the model, but I will keep it in mind for the future.

 

 

Apart from the hazardous gases, heat was also a problem in the tunnels. Northern Pacific did some tests in their tunnels on Stampede Pass in Washington State in the 1930s, using one of their biggest steam engines of the time. In one test, on entering a tunnel, the cab temperature went from 49 Fahrenheit to 130 Fahrenheit in 90 seconds ! Later, following the principle of the SP cab-forwards, they tried running the engine backwards. Cab temperature went from 80 to only 92 degress, but the temperature in the dynamometer car, behind the engine, went up to 140! Based on these tests, NP drew up designs for their own cab-forwards, but these were never built. Instead, they converted to diesels (which have their own problems with tunnels - see the tunnel motors).

 

 

That does sound unpleasant . Do you know any resources about these planned NP cab-forwards?

[Willy]

Thank you for that post Dominik, good photos and a good run-down on the raison d'??tre for these interesting locos.

 

 

Cheers,

 

 

Willy

 

 

[pH]

Do you know any resources about these planned NP cab-forwards?

Dominik, the only information I have comes from the June 2000 (Issue#260) of 'CTC Board', page 54. It's just a sidebar to a main article, which was the first part of a three-part series on NP's Stampede Pass. The pass was then being re-opened after several years out of service. It refers to NP erection drawings for a cab forward being completed in September 1939, and finishing drawings being done by Baldwin two years after that. 4-6-6-4 and 4-8-8-2 versions were proposed, but not built. There is a very small scale reproduction shown of the Baldwin drawings for the 4-8-8-2.

[signalmaintainer]

Dominik, the only information I have comes from the June 2000 (Issue#260) of 'CTC Board', page 54. It's just a sidebar to a main article, which was the first part of a three-part series on NP's Stampede Pass. The pass was then being re-opened after several years out of service. It refers to NP erection drawings for a cab forward being completed in September 1939, and finishing drawings being done by Baldwin two years after that. 4-6-6-4 and 4-8-8-2 versions were proposed, but not built. There is a very small scale reproduction shown of the Baldwin drawings for the 4-8-8-2.

 

As pH mentioned, suffocating heat and asphyxiation from exhaust inside Stampede Tunnel were work-a-day risks for NP train crews. Dubbed "Stampede Hell," no other tunnel in the country has as sinister a reputation. The reason is that the 2.2 percent adverse grade crests midway through the tunnel and immediately begins a 2.2 percent descent. The resulting arch provides a convenient collection point for heat and gasses. The ventilation system (now defunct) offered some help, but still could not offset what a laboring steam locomotive could produce during the 1.8-mile journey through Tunnel 3. Double-heading must have been a nightmare for the crews of the trailing locomotive.

 

Passengers and crews suffered alike. Indeed, I've ridden in the cab of a freight westbound over Stampede Pass, and both directions in the air-conditioned coach of a passenger excursion. The exhaust stench is formidable, and in the coaches the heat buildup was truly remarkable.

 

Stampede Tunnel also is narrow, loading gauge being almost impassable for NP's big articulated Z-6 through Z-8 4-6-6-4 Challengers. Nonetheless, the NP reportedly did attempt something similar to the SP, trying a Challenger in reverse through Stampede Tunnel. It must have been a nerve-wracking trip for the crew.

 

I would assume that any cab-forward design the NP debuted would have been something about the size the older Z-3 2-8-8-2s, but a simple articulated like the Challengers rather than a Mallet. However, it all became moot when the NP acquired 11 of the new EMD FT diesel in January 1945 and assigned them quickly to Stampede Pass to replace the aging Z-3s.

[NGT6 1315]

Thanks once again for your replies . One other thing I read about the SP cab-forwards was that there once was an accident where the fuel oil pipes into the firebox on the engine in question were leaking so badly that the train got stalled in the middle of a tunnel due to loss of adhesion. The oil then ignited right under the cab, resulting in engineer and fireman being killed.

[Oldddudders]

Thanks for the heads-up, Ian - does this apply to the AC-12 specifically or to other IM models as well? And, do you know when the botched batch was shipped to the dealers? Mine received his latest load only in early December.

 

Right now this is not much of an issue for me anyway as I have no place to run the model, but I will keep it in mind for the future.

This was what I read, and it sounds pretty damning! If you are affected, your dealer needs to hear about it now, I suggest, rather than in a while when you have the layout built and discover the loco is a dog!

 

http://www.tonystrains.com/tonystips/2009/121009.htm

 

I'll keep my fingers crossed for yours not being affected!

[signalmaintainer]

This was what I read, and it sounds pretty damning! If you are affected, your dealer needs to hear about it now, I suggest, rather than in a while when you have the layout built and discover the loco is a dog!

 

http://www.tonystrai...2009/121009.htm

 

I'll keep my fingers crossed for yours not being affected!

 

This is one beautiful model, and I sure hope they run better than a middle-aged signal maintainer in work boots!

 

Wow, oil fire under the cab. That's a dreadful thought.

[pH]

A search for something else turned up this very old topic. People may (or may not - it's your choice!) be interested in this locomotive, reckoned to be the first 'cab forward' ever built - http://oldtomstoys.com/north-pacific-coast-21-thomas-stetson/

[dullsteamer]

Nice model, Dom, hope you don't have any problems with it.

 

The silver colour on the smokebox wasn't intended to improve visibility. You'll notice that unlike the boiler barrel, the smokebox doesn't have any lagging or cladding, so SP used an aluminium-based heat resistant paint as a protective finish. The unlagged area at the bottom of the firebox around the foundation bar/mud ring was also finished with that paint.

 

Cheers,

 

Mark.