|Class||Qty.||Road Numbers||Year Built||Builder||Notes|
Only one 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 two-coupled axle forward and the three-coupled axle in the rear, and to duplex-drive them with conventionally arranged pistons. This resulted in the Q2, described in 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.
The Q2 was a rigid-wheelbase locomotive that was subdivided into two 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.
The Q2 was credited 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, the Q-2 was a powerful machine in actual service as well, but he did not think the power worth the Q2's liabilities:
"Things get interesting, however, when you realize the Q2 is, in effect paying a dead weight penalty of 43,220 pounds for 1000 more indicated horsepower at 57 miles per hour [than that developed by the J1]." He concedes that piston thrusts were lower but at freight-train speeds the J1 wouldn't encounter much stress. Against those modest positives, Ball arraigned the Q2 on several charges:
"The Q2's did not know how to conserve water and in short time enginement were told to plan 'no more than an hour and a half of hard running before needing water'". They also were maintenance hogs: "When all the Q2s developed leaks in the barrel seam of the boilers just ahead and back of the second set of cylinders [probably due to frame stress], extensive work was required to do the caulking of the boilers."
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.
Baldwin's works numbers were 62451-62452 in 1940 and 72764-72766 in November 1945; 72767-72768 in December; 72769 in January 1946; 72770-72772 in April; 72773-72776 in May; 72777-72780 in June; 72781-72784 in July; 72785-72788 in August.
The Pennsy's own Juniata shops turned out 5500-5524 simultaneously; their works numbers were 4560-4563 in November 1945, 4564-4568 in December, 4569-4570 in January 1946, 4571-4574 in February, 4575-4577 in March, 4578-4580 in April, 4581-4582 in May, and 4583-4584 in June.
The first two engines for the Pennsy in this arrangement were the 6110-6111, built by Baldwin in 1942. An February 2011 email from Mr Andrew Fields pointed out that the only difference between the two was that the 6111 had a Franklin booster engine on the rear truck that added 13,500 lb to the starting tractive effort.
Most sources including surviving locomotive diagrams prepared by the Pennsy itself give the 1,430 sq ft superheater area shown in the specs, but it's worth noting that the 1947 Locomotive Cyclopedia credited the superheater with 1,680 sq ft (156.05 sq m) on page 213.
Setting the style for the fifty that followed (many felt prematurely) in 1945-1946, the 6101s had Franklin poppet valve gear, Raymond Loewy styling with a chisel nose, disc drivers, and most unusually, a rigid wheelbase of four axles divided into two 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.
Another source of difficulty was the Type A oscillating-cam system that operated the poppet valves. Train Forums contributor David Stephenson, writing as "feltonhill" in a post dated 21 August 2007 (http://cs.trains.com/TRCCS/forums/p/102289/1189982.aspx), described the mechanism: "Oscillating cams took their motion from a gearbox containing what amounted to a pair of miniature Walschaerts valve gears. The valve drive cam moved through a small arc but did not fully rotate 360 degrees. Cutoff was controlled within the gearbox mechanism."
Pointing out that other oscillating-cam systems were installed in accessible places on locomotives, feltonhill reports that the T1's installation was: "...a mechanic's nightmare. Although the drive boxes themselves were considered fairly reliable, their location was about as inaccessible as one can imagine and routine mainenance suffered accordingly. The front box was under the "hood" of shrouding on the pilot deck, behind the aftercooler and between the air pumps ...or the rear engine set, the box was located behind the cylinder saddle and positioned vertically between the frames. Nice place to work. Oh, and just for further complication, it was a mirror image of the front drive box."
5500 was converted to a rotary-cam valve system in July 1948 and 5547 was fitted with Walschaert gear in July 1949. The rotary-cam drive's cam "...operated more like those in IC engines, i.e., it rotated 360 degrees and the valve timing was controlled by the contours machined into the cam." Both conversions are reported to have been more reliable and maintainable.
Nine of the engines later had their cylinder diameters reduced by an inch to 18 3/4" (470 mm).
Stephenson offered a more complex view of the design 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):.
He says that C & O tests of the T1 in regular passenger service 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 other 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."
Ultimately, 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."
|Specifications by Steve Llanso of Sweat House Media|
|Railroad||Pennsylvania (PRR)||Pennsylvania (PRR)||Pennsylvania (PRR)||Pennsylvania (PRR)|
|Number in Class||1||26||1||52|
|Valve Gear||Walschaert||Walschaert||Walschaert||Franklin poppet|
|Locomotive Length and Weight|
|Ratio of driving wheelbase to overall engine wheebase||0.49||0.49||0.41||0.49|
|Overall Wheelbase (engine & tender)||107.83'||107.62'||123.75'||107'|
|Axle Loading (Maximum Weight per Axle)||73700 lbs||79780 lbs||71680 lbs|
|Weight on Drivers||354700 lbs||393000 lbs||281450 lbs||279910 lbs|
|Engine Weight||593500 lbs||619100 lbs||608170 lbs||502200 lbs|
|Tender Light Weight||412900 lbs||430000 lbs||451840 lbs||442500 lbs|
|Total Engine and Tender Weight||1006400 lbs||1049100 lbs||1060010 lbs||944700 lbs|
|Tender Water Capacity||18000 gals||19200 gals||24230 gals||19200 gals|
|Tender Fuel Capacity (oil/coal)||37.5 tons||37.5 tons||26.5 tons||42.6 tons|
|Minimum weight of rail (calculated)||118 lb/yard||131 lb/yard||117 lb/yard||117 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||300 psi||300 psi||300 psi||300 psi|
|High Pressure Cylinders (dia x stroke)||23" x 28"||19.75" x 28"||22" x 26"||19.75" x 26"|
|Low Pressure Cylinders (dia x stroke)||19.5" x 26" (2)||23.75" x 29" (2)|
|Tractive Effort||81794 lbs||100816 lbs||76403 lbs||64653 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.34||3.90||3.68||4.33|
|Firebox Area||580 sq. ft||725 sq. ft||660 sq. ft||490 sq. ft|
|Grate Area||121.70 sq. ft||121.70 sq. ft||132 sq. ft||92 sq. ft|
|Evaporative Heating Surface||5518 sq. ft||6725 sq. ft||5661 sq. ft||4209 sq. ft|
|Superheating Surface||2290 sq. ft||2930 sq. ft||2085 sq. ft||1430 sq. ft|
|Combined Heating Surface||7808 sq. ft||9655 sq. ft||7746 sq. ft||5639 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||409.82||677.37||247.44||228.28|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||36510||36510||39600||27600|
|Same as above plus superheater percentage||47098||47463||50292||34500|
|Same as above but substitute firebox area for grate area||224460||282750||251460||183750|