I dug out some Lionel model trains for my Christmas decorations and a man commented on the steam engine I had in the window a 6-8-6. On the internet it is a Pensylvania S2 and that only one was ever built in 1944 and that it was scrapped in 1953. Does anyone know anything about this engine. The picture on the internet is definitely the same as my lionel O-gauge model.
Just briefly, the Pennsy S-2 was a steam turbine drive locomotive, that is it used turbines to propel it forward and backward as opposed to a conventional valve-and-piston arraingement. Theoretically it sounded good, and was a good performer at high speed, but a bit of a steam hog at low speeds. It proved to be a dead end so only one was built. Interestingly, the S-2 was a great success for Lionel, one of their best sellers. In fact, the S-2 was better for Lionel than it was for the Pennsy!
The S class of locomotives were experimental. The S2 was built in collaboration between the PRR, Baldwin locomotive works, Westinghouse, and ALCO. It was designed and built during the war and the war production board limited material used for locomotives. It is a big surprise that the loco was built at all. The WPB limited railroads to existing designs only but the Pennsy must have had some political clout to overcome some of the restrictions. Original design was going to be a 4-8-4 but due to light weight alloys were restricted to war production the locomotive turned out too heavy and needed 3 axle trucks fore and aft.
As an experimental design it had some teething problems. Steam leaks from the turbines was one. Gearing issues were another. Water usage at low speed was too much to overcome. Turbine destruction was the final straw. There was quite a lot of speculation that if it was built as originally designed it would have performed better. Steam driven turbines were in their infancy when it was built and better metallurgical material was developed after it was scrapped. Variable geometry turbines could have helped in the slow speed usage of steam. As it stood it was a power house when it was running. On the test plant it nearly produced 6000 indicated horse power at 60 MPH. Starting tractive effort was low due to gearing issues and gears not strong enough for the loads put on them. Yes. There was a transmission in the locomotive. It was needed to reduce the RPM of the turbine.
If it was not for electrification and the growing and expanding diesel market they may have spent more research money into it.
Pete.
P.S. its nickname was Swoosh and sometimes Big Swoosh.
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
The latest issue of Classic Trains has a nice article about this locomotive.
The biggest 'teething problem' turned out to be not so much the turbine as the boiler and its front-end arrangement. A little watch-building first: Steam turbines need low exit pressure for best efficiency. Conventional wisdom holds that turbines on locomotives aren't 'preferred' as they are on ships because the latter have efficient condensing at the required high mass flow. There is also a requirement for very high volume (and good flow smoothing) in the exhaust tract from the turbine to clear the required large volume of low-pressure steam.
Meanwhile, while turbines produce very good torque at low speeds (a point the PRR motive-power department was at some pains to emphasize) there is higher steam flow through the device at low rotational speeds (in an axial-flow turbine, the potential reaction energy can't be extracted as rotation, with the effect that some of the steam just 'flows through' -- as an amusing side-note, this apparently got Parsons, the inventor of the axial-flow turbine, in trouble at school because he'd invented an engine that "obviously" had a 40% free-area leak straight through... ;-}). As it turns out, there is also relatively higher leakage at the 'tips' of the blades, both due to required clearance there and to vortex generation.
The S2 handled the additional mass-flow requirement by having four stacks and nozzles (you can see this in overhead pictures of the locomotive. The problem, as it turned out, was that the combination of leakage and power flow through the turbine at low speed ALSO produced sharply higher drafting on the fire, with comparatively rapid onset. I also suspect that any propensity for the engine to slip would result (as with the poppet valve gear on the T1s) in sustained very high mass flow and, in the S2 design, monstrously amplified draft flow.
Remember that the S2 boiler was of conventional design and construction (riveted and staybolted) running at what was by that time well-known to be an 'edge-of-the-envelope' pressure for that kind of structure. Perhaps unsurprisingly, by 1946 we begin to see evidence of staybolt failures -- some of them VERY severe and extensive. Doing a bit of 'reading between the lines' in the surviving correspondence at the Hagley, it's pretty clear that this was the nail in the S2's coffin.
It should be remembered that this was NOT the PRR's developed design for steam-turbine power. That was the V1 locomotive, greenlighted for production in 1944. This used two turbines, each geared to 4 individual axles with 48" wheels, and a "modified Q2" boiler. I have a copy of the tractive-effort chart developed for this locomotive, and it is interesting to observe just how competent the design was -- even before it was given a self-excited variable-torque transmission, the Bowes drive, which imho would have assisted dramatically in reducing the problem with low-rotor-speed "slip".
Unfortunately the V1 shared with the Q2 a colossal appetite for water -- something that F-units, for example, did not suffer from...
RME
Welded construction had been approved by ASME (in 1943) but none of the postwar PRR engines had it (this might have helped with the waist-sheet problems on the Q2s, but I digress) --
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