Class Q1 (Locobase 349)

Only 1 Q1 was built in 1942. The duplex-drive idea, which had also smitten the Pennsy in the passenger field, took hold of its freight engine designers, too. The Q1's drivers were tall for a freight engine. Its rear two cylinders were reversed under the cab (rods moving forward) to drive the two axles of the second group on the rigid frame. The cylinders sizes and strokes were unalike, which except for compounds, is so unusual as to be unique. The front pair had 23-in diam pistons with a stroke of 28 inches, the rear pair had 19 1/2-in diam pistons with a shorter 26-in stroke.

After further testing, the Pennsy decided to place the 2-coupled axle forward and the 3-coupled axle in the rear, and to

duplex-drive them with conventionally arranged pistons. This resulted in the Q2, described in Locobase 350.

Class Q2 (Locobase 350)

It's difficult to see what the Pennsy gained in designing this duplex-drive locomotive so late in the steam locomotive's day. (See Locobase 349 for the single Q1 trial horse.) It is possible that the lesser weight of each driving set (cylinder, main rod, side rods) allowed smoother running at higher speeds. It is, in most respects, virtually identical in size, power, and weight to the J-class 2-10-4s that Pennsy built according to an earlier C&O design, although the tractive effort was 5.5% higher.

It is credited, however, with having developed 8,000 peak horsepower. In tests, the Q2 reached 7,987 hp at 57.4 mph evaporating 16,600 gal of water per hour and burning 12.5 tons of coal. According to Don Ball, at least, the Q-2 was a powerful machine in actual service as well.

The Q2 was a rigid-wheelbase locomotive that was subdivided into 2 axle groups: the forward pair of axles were driven by 19 3/4-in diameter cylinders with a stroke of 28 inches. The rear cylinder pair, located between the front axle and the 3-coupled rear group, had 23 3/4-in diam cylinders with a stroke of 29 inches. A trailing truck booster added 15,000 lb to the already high starting tractive effort. The engines were large and attractive with an air-smoothed casing similar to that of the SP's 2-8-8-4. 26 were built, including 6131 and the 25 built in 1945-1946.

Class S1 (Locobase 347)

Passenger locomotive design run wild was the S1. A single example was built in time for the 1939 New York World's Fair, where it was displayed on a treadmill operated by its own steam. COD price was $669,780.

Unfortunately, this exceptionally long engine and tender combination, styled by Raymond Loewy, was prone to slipping and was much too large for most service. Staufer (1968) agrees that she was oversized and thus unable to visit most roundhouses or handle tight curves, but contends: "She was an excellent steamer and gave trouble-free service." Indeed, this engine is regarded as the unofficial speed record-holder for steam by many because of runs she reportedly made pulling 850 to 1000-ton trains at 140-145 mph. Note that this high speed is made pulling a weight of train most other passenger locomotives couldn't get up to 50 mph.

Note the very tall drivers, odd-ball 3-axle leading and trailing trucks, and large tender.

The usual tractive effort figure is given as 71,900 lb at 80% cut-off. The figure given in the table permits easier comparison with other engines, most of which have indicated TEs based on the 85% efficiency factor.

Class T1 (Locobase 348)

The first 2 engines for the Pennsy in this arrangement were the 6100-6101, built by Baldwin in 1942. Setting the style for the 50 that followed (many felt prematurely) in 1945-1946, the 6100s had Franklin poppet valve gear, Raymond Loewy styling with a chisel nose, disc drivers, and most unusually, a rigid wheelbase of 4 axles divided into 2 groups, each of which was driven by a pair of cylinders.

The theory behind the duplex drive held that reducing the masses of reciprocating (e.g., main and side rods) and revolving (e.g., cranks and counterweights) would reduce hammering and raise speed. Tests run at a high boiler pressure and late cut-off showed 6,110 drawbar horsepower at 85 mph. In service, these engines could be fast, powerful, and smooth, pulling 910-ton passenger trains at 100 mph.

According to most sources, the divided drive proved to be a major maintenance headache, however, because no way could be found to stop one or the other driver-cylinder set from slipping, either starting or, more alarmingly, at high speed. This liability proved fatal to the chances for real success for these engines, and they were retired well before the much earlier vintage K-4 Pacifics.

But David R Stephenson, writing in the May 2005 Chesapeake and Ohio Historical Magazine (reproduced online at http://www.findarticles.com/p/articles/mi_qa3943/is_200505/ai_n1342634, accessed 24 Oct 2005), says that C & O tests of the T1 in regular passenger service suggest otherwise. He contends that the C & O's reports show that:

"They handled trains well, particularly at higher speeds.

"They kept schedule and made up delays on most runs.

"They had no excessive tendency to slip.

'The stall at Waynesboro [a September 12, 1946 event often offered as a primary example of the design's slipping tendency] was caused by overloading."

Stephenson's meticulous, and thankfully clearly written, account of the September 1946 tests nevertheless shows some design weaknesses, particularly in starting trains. And he argues that the duplex solution was conceived to redress a potential problem that never quite materialized. As designers of 4-8-4s came to grips with counterbalancing and stress issues, they came up with such classics as the UP FEFs (Locobase 284), the Santa Fe 2900s (Locobase 271), the N & W Js (Locobase 274), and ultimately the S-1 Niagaras of the New York Central (Locobase 5582). "Here was a locomotive," Stephenson 's verdict concludes, "that could match the T1 at all but the highest speeds, and do it day-in and day-out without special treatment."

And the T1s' early departure from service came not from their own peculiar shortcomings, says Stephenson, but from the triumph of the diesel's "...superior economics ...and their immediate application to PRR's heaviest and most prestigious trains ...In the face of dieselization, the T1 just didn't matter."

A discussion on the Trains forum -- http://www.trains.com/TRC/CS/forums/482004/PrintPost.aspx -- gives details on the N & W in 1948.