PRR S2 vs Q2

Mike: The S and Q denote the wheel arrangement, the 2 denotes a different, later engine using the same wheel arrangement. For example, the first S-1 was the duplex that was displayed at the 1939 World's Fair, a 6-4-4-6. The S-2 was the Turbine, also a 6-4-4-6, the drivers being thus: the first 4 were driven for forward revolution, the rear for were for reverse (sounds weird, doesn't it?). If you get on Wikipedia, you can find photos and more detail about other PRR engines that were experiments like these.

Good question. All I know about these particular engines and their designations comes from having a couple of them. But my favorite is actually the Q1, made by 3rd Rail some years back in skirted and unskirted versions. I have the former and it represents another one of those innovative engines that was basically a failure in service. 

These are 3rd Rail production sample photos issued at the time. The first shows the reversed cylinders at the rear of the odd 4-6-4-4 configuration. It is quite a sight watching it run perfectly at the low speeds the 3rd Rail drive train allows for.

The PRR used letter designations for their locomotives.  Single letters for steamers (S1) and two (or more) letters for diesels (AF15, FRS16).

For the most part, the number for steamers was for the version of the engine (HP for diesels).  For example, K was for the 4-6-2 wheel arrangement steamers.  The first K, K2 (no K1), was built in 1910.  The K4, the most successful of the Ks, was built in 1914.  There was even a K5, but only two were built.  A was for 0-4-0, B was for 0-6-0, E was for 4-4-2, etc.

The Q was the same, sort of.  They both had 10 drivers, and being rigid framed were like 4-10-4s.  The Q1, built in 1942, had the 4-6-4-4 wheel arrangement with the rear cylinders facing backwards as seen below:

This allowed huge drivers (77") for fast freight service.  Unfortunately, this resulted in a smaller firebox (could not keep steam pressure up at speed), was harder on the rails, and the cylinders keep getting dirty due to the close proximity of the firebox.  Only one Q1 was made.

Pennsy liked the 10 driver concept so modified the Q1 to a standard cylinder arrangement in 1944 and called it a Q2:

The 4-4-6-4 wheel arrangement resulted in smaller drivers (69") with the Q2 turning out to be one of Pennsy's most successful steamers, with 25 built. 

The S engines, S1 and S2, did not follow the wheel arrangement naming.  I don't have pictures of these, but the S1 was Pennsy's huge 6-4-4-6 engine built in 1939.  The S1 was too big to be practical and only one was built.  Since no more were to be built, the S designation was available for another engine.  The S1 lasted until after WWII mainly because the Pennsy needed motive power during the war.

When the Pennsy experimented with their 6-8-6 steam turbine engine in 1944, they called it a S2.  The S2 was a good engine at high speed, but very inefficient at slow speeds.  Again, only one was built.  The S2 was good enough to keep on the Lines West tracks because of the long straight sections where it could stay at speed.  It was retired in 1949 after it was damaged.

The PRR had successful 2-10-4's.  Was the Q a locomotive too far?

Dominic Mazoch posted:

The PRR had successful 2-10-4's.  Was the Q a locomotive too far?

The Q2 was a successful design, it just came too late as Pennsy's management finally decided diesels were the future (they were one of the last class 1 railroads to make that decision). The Q2 was built in Pennsy's own shops.

Pennsy's J1 2-10-4 was also a very good engine built in 1942, but it was a C&O design from 1930.  The J1 was forced on the Pennsy because wartime restrictions would not allow a new, unproven design.  As soon as the war was over, the Pennsy went to the Q2.

The Q2 and J1 were Pennsy's superpower fast freight engines.  While the M1s were good dual service engines, and the N1/2s were good haulers, neither could match the Q2 or J1.  The arrival of diesel road engines starting in 1946 signaled the beginning of the end of steam on the Pennsy.

I seriously doubt the boilers had anything in common.  

However, the K4, L1, and I1 had more or less the same boiler, and from a modeling standpoint at least, the E6, H10, and G5 boilers are almost interchangeable.

bob2 posted:

I seriously doubt the boilers had anything in common.  

However, the K4, L1, and I1 had more or less the same boiler, and from a modeling standpoint at least, the E6, H10, and G5 boilers are almost interchangeable.

K4 and L1 boilers were indeed the same, differing in the location of the sand dome.  However the I1 boiler had a lot more in common with the M1 than it did with the K4/L1.