While there may be many oddball locomotive designs out there, few ever left the imagination or the drawing board. The 2-8-8-8-2 Erie P-1 'Triplex' is one of the exceptions. It was designed, simply put, to be the most powerful steam locomotive and in 1914, when it was built, it was. Three examples (originally numbered 2603-05 later 5014-16) were built by Baldwin for Erie and, in 1916, a single 2-8-8-8-4 was built for Virginian. Virginian had little success with their Triplex, but Erie kept their three engines in service for 13 years.
The engine is powered by a compound arrangement. High pressure steam enters the second set of cylinders, and the exhaust from these is fed into the other four. The front cylinders then exhaust into the smoke box, while the rear set exhaust through a feedwater heater and out the pipe in the back of the tender. This had the unfortunate effect of reducing heat for stoking the firebox.
The Triplexes' 6 cylinders and 24 drivers added up to a massive amount of tractive effort, but the boiler, though large for the time, was not large enough to keep up with the cylinders' demand. Thus, speeds above 10mph could not be sustained. The Triplexes were therefore used for heavy pusher service.
Because there are drivers under the tender, the Triplex may be counted as one of the largest tank engines ever built. A downside of this arrangement, however, is that as water and coal are expended, the weight on the rear drivers decreases, impacting tractive effort.
Ultimately, this design could not be called a success, and no other such engines were ever built, however that it was built at all is interesting enough. My model is built on 24 Big Ben large drivers. It is fully articulated, and capable of navigating any track layout. The cab is 8 studs wide. The boiler, based on Richard Lemeiter's Mikado Engine, is just under 6 wide. I had to keep the cylinders as narrow as possible as well to maintain the look, and 9 was the minimum I could manage. Many of the surviving images show different configurations of this locomotive. In fact, most of the pictures I've seen show the boiler in raw steel color (a light blue). I am going to attempt this configuration when time allows. There is room in the tender for a medium Power Functions motor and a battery, and these will ultimately be what powers it. I have already found that one 9v motor is sufficient to pull it around the track, so I believe one PF medium should work as well. It will be geared down for maximum slowness accuracy.