| Pennsylvania Railroad S1 | |
| Powertype: | Steam |
| Builder: | PRR Altoona Works |
| Serialnumber: | Altoona 4341 |
| Builddate: | 1939 |
| Totalproduction: | 1 |
| Uicclass: | 3′BB3′ |
| Leadingdiameter: | 360NaN0 |
| Driverdiameter: | 840NaN0 |
| Trailingdiameter: | 420NaN0 |
| Wheelbase: | Coupled: 26feet, Loco: 64feet, Loco & tender: 123feet |
| Length: | 140feet |
| Width: | 10feet |
| Height: | 16feet |
| Locoweight: | 6081700NaN0 |
| Weightondrivers: | 281440sigfig=4NaNsigfig=4 1st Driver: 738000NaN0, 2nd Driver: 731300NaN0, 3rd Driver: 669700NaN0, 4th Driver 674600NaN0 |
| Tenderweight: | Empty: 197020sigfig=4NaNsigfig=4; Loaded: 451840sigfig=4NaNsigfig=4 |
| Locotenderweight: | 10600100NaN0 |
| Tendertype: | 250 P84 16-wheel tender (two 4-axle trucks) |
| Fueltype: | Coal |
| Fuelcap: | 52900sigfig=1NaNsigfig=1 |
| Watercap: | 24230usgal |
| Boiler: | 1000NaN0 |
| Boilerpressure: | 300lbf/in2 |
| Firearea: | 132square feet |
| Tubesandflues: | 219 tubes (2.25 in), 69 flues (5.5 in). |
| Cylindercount: | Four |
| Cylindersize: | 22x |
| Fireboxarea: | 6601NaN1 |
| Superheaterarea: | 20851NaN1 |
| Totalsurface: | 77461NaN1 |
| Valvegear: | Walschaerts |
| Tractiveeffort: | 764032NaN2 (at 85% cut-off) or 719002NaN2 (at 70.6% cut-off) |
| Factorofadhesion: | 3.68 |
| Poweroutput: | 7,200 hp when hauling 1,200 tons train at 100mph |
| Maxspeed: | 152mph (Claimed) Operating speed ≤ 120mph |
| Operator: | Pennsylvania Railroad |
| Fleetnumbers: | 6100 |
| Retiredate: | 1946 |
| Disposition: | Scrapped 1949 |
The PRR S1 class steam locomotive (nicknamed "The Big Engine") was a single experimental duplex locomotive of the Pennsylvania Railroad. It was designed to demonstrate the advantages of duplex drives espoused by Baldwin Chief Engineer Ralph P. Johnson. The S1 class was the largest steam locomotive ever built.[1] The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy.[2] [3]
The S1 had a unique 6-4-4-6 wheel arrangement, meaning that it had two pairs of cylinders, each driving two pairs of driving wheels. To achieve stability at fast passenger train speeds (above 100 mph), articulation was not used. The S1 was completed on January 31, 1939, at Altoona shop, and was numbered 6100.
At 140feet overall, engine and tender, the S1 was the longest reciprocating steam locomotive ever; it also had the heaviest tender (451,840 lb / 205 tonnes), highest tractive effort (764032NaN2) of a passenger steam engine when built and the largest driving wheels (7 feet in diameter) ever used on a locomotive with more than three driving axles. The problem of wheel slippage, along with a wheelbase that was too long for many of the rail line's curves, limited the S1's usefulness. No further S1 models were built as focus shifted to the much smaller but more practical class T1 in June 1940. Design of the 4-4-4-4 T1 and the 6-4-4-6 S1 occurred concurrently, however, the S1 was the first produced.
As early as June 1936, the management of Pennsylvania Railroad decided to build a new passenger locomotive to replace its aging K4s locomotives. They also hoped that the new S1 steam locomotive would have a performance equal to their Pennsylvania Railroad class GG1 electric engine and would be capable of hauling a 1,000-ton passenger train at 100 mph. A conference was held between Baldwin Locomotive Works officials and W. F. Kiesel, J. V. B. Duer and W. R. Elsey for PRR, where PRR demanded a passenger locomotive to haul 15 standard cars at 100 mph on level track between Paoli and Chicago. Baldwin presented several 4-8-4 and 4-4-4-4 designs made for other railroads. However, PRR rejected the 4-8-4 design in favor of a rigid frame duplex and asked Baldwin to consider the wheel arrangement 4-4-6-4. In July 1936, PRR requested Baldwin Locomotive Works to submit a design for a 4-8-4 engine capable of handling a 2,000-ton train between Colehour and Harsimus Cove.
Two months after the conference, Baldwin Locomotive Works officials presented four designs to PRR:
PRR preferred 4-4-4-4 and asked Baldwin to consider a passenger version with 6 ft 8 in drivers and a freight version with 6 ft drivers. However, the cooperation between PRR and Baldwin, which proceeded without signing any agreement or contract for the development of the new high-speed duplex engine, didn't go smoothly. Ten months after the first conference (April 1937), PRR ended Baldwin Locomotive Work's consultation and assigned the task to a consortium of Baldwin Locomotive Works, American Locomotive Company, and Lima Locomotive Works under a joint contract. T. W. Demarest headed the joint committee, General Superintendent of Motive Power in PRR's Western Region.[4]
The members of the joint committee were:
On 28 April 1937, PRR's Board authorized $300,000 for this experimental high-speed passenger locomotive project. The design started with a 4-4-4-4 duplex.
On 2 June 1937, PRR officially announced the development of the “Pennsylvania Type” high-speed passenger locomotive which would become Class S1. After various details were discussed and finalized, it became necessary to make changes that substantially increased the locomotive's weight. By the time the plans were finalized and approved it had evolved into a 6-4-4-6.[5]
The benefits of a duplex design included lighter machinery, shorter cylinder stroke, less wear, lower piston thrust, smaller more efficient cylinders, and a more stableframe than an articulated underframe; also, no hinged connection had to be maintained.[6] Reduced hammer blows on the track resulted in lower maintenance cost. Two sets of drivers with four wheels each could have lighter (as much as 25%) running gear than a locomotive with all four axles coupled together, smaller and lighter moving parts ensured less wear and tear. Baldwin's chief engineer believed that the 8-coupled, two-cylinder locomotives of the time were at or near practical limits in terms of steam flow, cylinder efficiency could be improved at high speed by getting the same power from four smaller cylinders with proportionately larger valves. Valve travel in S1's cylinder was 7-1/2 in, the lap was 1-7/8 in, the lead was 5/16 in, exhaust clearance was 0.25 in, valve diameter was 12 in.
The S1 was the largest passenger locomotive ever constructed, and the cast steel locomotive bed plate made by General Steel Castings was the largest single-piece casting ever made for a locomotive.[7] In order to negotiate sharper radius curves, S1 was equipped with lateral motion devices made by Alco on its first and third set of drivers, allowing 57.2 mm (2.25 inches) of lateral play on the axles, but these proved to be inadequate. Unlike other experimental duplex engines like PRR's Class Q1 #6130 4-6-4-4, there were no flangeless wheels or blind drivers adopted on S1.
In March 1938, a Chicago and North Western class E-4 4-6-4 "Hudson" #4003 was tested by PRR at Altoona.[8] Based on the test results, PRR decided to adopt 84" drivers and a cylinder pressure of 300 psi for the S1. PRR believed that the large diameter drivers could increase the tractive effort without causing undue slipping.[9] In August 1941, PRR VP-Western Region James M. Symes, a senior official who turned against the idea of duplex engine in later years, approved the extension of stall no. 30 of the Crestline roundhouse to accommodate the S1. The stall had a connection at the back because the S1 could only be turned on a wye, but not on the roundhouse's turntable.
Timken roller bearings were equipped on the crosshead pins, all engine trucks, and drive axles as well as the tender trucks. Besides, the lightweight reciprocating parts were manufactured by Timken High Dynamic Steel and designed by Timken engineers.[10] To get enough steel between the crank and axle, the back end of each main rod was offset NaNinches from the crank in the driver, so the big end made a 260NaN0 circle while each side rod pin made a NaN0NaN0 circle.
The boiler for the S1 was the largest built by the Pennsylvania Railroad; with 660square feet of direct heating surface and 500 one-inch diameter tubes, the total heating surface area of S1 was 7746square feet; it was 99.3% as massive as the boiler for Union Pacific's 4000-class "Big Boy" locomotives. In terms of drawbar horsepower, the S1 was 13% more powerful than the Big Boy, with and respectively. The large Belpaire firebox met the Pennsy's standards; its heating surface area included that supplied by seven American Arch circulators. Water passed through 5.5-inch horizontal tube met at the centerline with the other cross tube forming the bottom of the 7-inch vertical tube that sprayed the water up into the steam space above the crown sheet. The lowest set pair of tubes was forward with the side openings of the other six steadily rising toward the back.
A large Worthington 6 SA feedwater heater was fitted with a 7 SA pump to handle the enormous boiler's thirst. The six-wheel leading and trailing trucks were added, as the locomotive was too heavy for four-wheel units. The streamlined Art Deco styled shrouding of the locomotive was designed by Raymond Loewy, a design concept based on his earlier streamlining design for PRR K4s #3768 in 1936, for which he received U.S. Patent No. 2,128,490. Raymond Loewy conducted the wind-tunnel test by using the clay model of S1 at Guggenheim Aeronautical Laboratory for the design of its streamlined shrouding, and it was the same laboratory where he conducted testing of the streamlining of PRR K4s #3768. The design of the smoke lifting plate around the smokestack on S1 was improved based on the wind-tunnel test result from Guggenheim.[11]
The cost of the S1 was $669,780.00, equal to $ today, which was over twice the cost of a PRR T1 4-4-4-4 (#6111 cost $310,676). No. 6100 was completed at Altoona on December 21, 1938 without the streamlined casing. On the same day, it made its first road test with two cars, running backward to Huntingdon and returned to Altoona at speeds up to . During the run, it was stopped and checked for overhang on all tight curves. Assistant Chief of Motive Power-Locomotive Carleton K. Steins (1891-1973) noted superior riding and steaming qualities.[12] During another pre-service road test, the S1 was clocked at towing 90 freight cars.[13]
The S1 was displayed at the 1939 New York World's Fair with the lettering "American Railroads" rather than "Pennsylvania Railroad", as 27 eastern railroads had one combined 17acres exhibit, which also included the Baltimore and Ohio class N-1. To reach the Fair, the S1 took a circuitous route over the Long Island Rail Road. Many obstacles, like some of the third rail guards, had to be temporarily removed while other obstacles were passed at a crawl to reach the fairgrounds. S1 was towed (facing backward) by smaller freight engines like PRR Ils and took a round-about route to the fair site. She ran up the Bel-Del, interchanged with the Lehigh and Hudson River Railway at Belvidere and NH at Maybrook. The S1 traveled over the Poughkeepsie and Hell Gate Bridge, crossed over the Hudson River and then brought it across on the NY Connecting.[14] On March 13, 1939, the S1, lettered “American Railroads” on the tender, arrived at New York World's Fair.
At the Fair, the drive wheels operated under the locomotive's steam power ran continuously on the roller platform at for an entire day. Film footage shows that all the wheels on S1, besides the drive wheels, were also placed on rollers powered by electricity; every time S1 started its performance by moving the drive wheels, all the wheels were rolling, including the wheels on the tender's truck.
The World's Fair was open for two seasons, from April to October each year, and was officially closed on October 27, 1940. During the five-month break between October 1939 and April 1940, No. 6100 was put back on the system for passenger service and road testing. There is photo evidence showing that the S1 was hauling the Manhattan Limited, a named train serving as an alternative to the Broadway Limited, in November 1939.[15]
Popular Mechanics described S1 as the "Pride of American Railroad" in an article in their June 1939 issue.[16]