The PRR S1 class steam locomotive (nicknamed "The Big Engine") was an experimental locomotive that was the largest rigid frame passenger locomotive ever built.^[1] The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy.^[1][2]

The S1 was the only locomotive ever built to use a 6-4-4-6 wheel arrangement. Also, the S1 class was a duplex locomotive, meaning that it had two pairs of cylinders, each driving two pairs of driving wheels. Unlike similar-looking articulated locomotive designs, the driven wheelbase of the S1 was rigid. The S1 was completed January 31, 1939 and was assigned locomotive number 6100.^[3]

At 140 ft 2 ¹⁄₂ in (42.74 m) over engine and tender the S1 was the longest reciprocating steam locomotive ever built; it could not negotiate curves on much of the PRR system. This problem, along with wheel slippage, limited the S1's usefulness. No further S1 models were built as focus shifted to the T1 class. The last run for the S1 was in December 1945 and the engine was scrapped in 1949.^[4][5]

Construction history[link]

In 1937, Pennsylvania Railroad officials decided to build a new passenger locomotive to replace its aging K4s locomotive. The PRR officials also hoped that the new S1 steam locomotive would have performance equal to their GG1 electric locomotive.^[5]

In a collaborative effort, the Pennsylvania Railroad, Baldwin Locomotive Works, the Lima Locomotive Works and the American Locomotive Company contributed to the experimental S1 design.^[5]

The S1 was the largest express passenger locomotive ever constructed, with an overall length was 140 feet 2+¹⁄₂ inches (42.74 m). At 77 feet (23 m) long and a weight of 97,600 pounds (44.3 t), the cast steel locomotive bed plate made by General Steel Castings was the largest single-piece casting ever made for a locomotive application.^[5][6]

The boiler unit for the S1 was the largest built by the Pennsylvania Railroad. The six-wheel leading and trailing trucks were added, as the locomotive's design became too heavy for four-wheel units. However, the locomotive was still overweight by a significant margin. The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy,^[1][2] for which he received U.S. Patent No. 2,128,490 The final construction cost for the S1 was $669,780.00.^[5]

World's fair display[link]

The S1 at the New York World's Fair of 1939

The S1 was displayed at the New York World's Fair of 1939 with the lettering "American Railroads" rather than "Pennsylvania Railroad", as 27 eastern railroads had one combined 17-acre (6.9 ha) exhibit, which also included the Baltimore & Ohio's duplex locomotive.^[6] To reach the New York World's Fair, the S1 took a circuitous route over the Long Island Rail Road. Many obstacles had to be temporarily removed and other obstacles were passed at a slow crawl to reach the fairgrounds. At the World's Fair the S1 was a dynamic display; the drive wheels operated under the locomotive's own steam power.^[5] This was done by placing the S1 on a platform that had rollers under the drive wheels. By using this type of display, visitors could see the duplex drive in use. After the World's Fair, the S1 was relettered and numbered for use in the Pennsylvania Railroad fleet. The S1 was used by the PRR for publicity purposes as well and its image was featured in calendars and brochures.

Service history[link]

Detail view of the driving wheels and cylinders; note the rollers upon which the wheels rested while on display

The S1 class locomotive was so large that it could not negotiate the track clearances on most of the lines of the PRR system. In its brief service life it was restricted to the main line between Chicago, Illinois and Crestline, Ohio. It was assigned to the Fort Wayne Division and based at the Crestline enginehouse. The S1 hauled passenger trains such as The General and The Trailblazer on this route.^[5] Crews liked the S1, partly because of its very smooth ride. The great mass and inertia of the locomotive soaked up the bumps and the surging often experienced with duplex locomotives.

Starting tractive effort calculated in the usual way (85% mean effective pressure) comes out 76,400 lb, but the engine used 70% limited cutoff (presumably to increase port openings at short cutoff) so the railroad claimed a correspondingly lower tractive effort.

Design flaws[link]

This unreferenced section requires citations to ensure verifiability.

The S1 had a serious design flaw; the locomotive had too small a fraction of its total weight on the driving wheels. “The Big Engine” put less than forty percent of her total weight on the eight driving wheels. The rest of her weight was carried by the massive six-wheel pilot (leading) and trailing truck. This left the two sets of four duplex driving wheels susceptible to wheel slippage, a dangerous condition for any steam locomotive.

When the powered wheels of a steam locomotive lose their adhesion to the rails and freely spin, the instantaneous result is over speed damage. If the locomotive's engineer does not detect and rectify this situation at once two things will occur, first, the metal tires that surround the driving wheels will be seriously damaged; second, the piston rods, their bearings and the other equipment associated with the reciprocating motion of the engine will be overstressed and destroyed; the engine will literally tear itself apart, by its operation at speeds well beyond the design limitations.

Normally, in a standard locomotive when starting under load from standing start, the engineer would observe his rearmost driving wheels and compare their movement to the relative forward movement of his locomotive over the ground. As locomotives grew larger, the engineer would have to listen to the rhythmic sound of the engine’s exhaust (the characteristic “chug-chug”) and compare the rhythm of this sound with the observed movement of his locomotive over the ground.

If, as he opened his engine’s throttle, the rate of increase of the “chug chug” sound was out of sync with the forward progress of his locomotive, he knew his wheels were slipping. A passenger locomotive with 72-inch-diameter (1,800 mm) drivers would travel twelve (12) feet or four (4) yards per “chug-chug”. It was therefore easy to correlate the rhythmic sound of the exhaust of a starting locomotive with the locomotive’s progress from a standing start. An engineer could thereby avoiding applying too much power to a starting locomotive (by opening the steam throttle valve too much, and too quickly) and causing the wheels to slip.

The S1’s duplex engine design meant that two separate engines were concurrently and in sequence exhausting into the single smoke stack. This made it nearly impossible for a locomotive engineer to distinguish the behavior of an individual engine set, based upon the sound of its exhaust. Unless both sets of engines experienced wheel slip simultaneously, the sound of the normal set would mask the sound of the set that was slipping and over speeding. If the wheels began to slip he would have no knowledge of this fact until he had already damaged the tires of the duplex engine’s wheels; or he heard the crashing sounds of a duplex engine tearing itself apart, in over speed.

The S1 had a further handicap in the area of slippage. Unlike virtually all other steam locomotives that faced wheel slippage when starting; the S1 (because of the very light weight on the driving wheels) would experience engine wheel slip over the road at operating speed. The adhesion of the wheels to the rails was so light, that even minor variations in the roadbed would cause either the forward or rearward duplex engines to slip. This hazard more than any other doomed the operating life of this engine. The loss of adhesion at speed (30 – 50+ mph) always did serious mechanical damage to the engine, which lost adhesion, and to the locomotive as well.

Alleged speed records[link]

It was hoped that the locomotive could haul 1,000 tons at 100 miles per hour, but this goal was not reached. While an article "Riding the Gargantua of the Rails" in the Dec. 1941 Popular Mechanics Magazine cites a speed of 133.4 miles an hour, there are apocryphal stories of the S1 reaching or exceeding 140 miles per hour, but there is no documentation of these and it is considered unlikely by experts.^[7]

Its high speed capability was such that some have claimed the S1 may have even exceeded the 126 mph (203 km/h) record steam locomotive speed set in 1938 by the LNER locomotive Mallard. The locomotive was also rumoured to have operated at speeds exceeding 156 mph on the Fort Wayne-Chicago Railroad, as it was rumoured that the PRR received a fine posted by an interlocking tower on the division, proving the claim. However, it appears that no verifiable records are available to authenticate the claims.^[7]

Removal from service[link]

No further S1 models were built. According to the cited reference the last run for the S1 6100 was in December 1945. However, a timebook belonging to Pennsy engineman Byron Breininger from the Ft. Wayne division records a trip to Chicago on S-1 engine 6100 at 8:59 AM on May 5, 1946. The engine was scrapped in 1949.^[4][5] The PRR continued developing the T1 class of 4-4-4-4 duplex locomotives but this locomotive model also met with limited success.

Modern culture[link]

This unreferenced section requires citations to ensure verifiability.

The design of the S1 has proved to be very popular:

• The S1 appears in the Sandman comic series, book IX.
• The S1 is was also represented in a (c)1939 painting by railroad artist Grif Teller that appeared in the Pennsylvania Railroad's picture calendar.
• A limited HO Scale brass model version of the PRR S1 was produced by Gem Models during the 1960s to the 1970s. These models are now very rare, although they could be found on eBay from time to time. Not much information exists about them.
• In the PC game Gadget: Invention, Travel, & Adventure, one of the trains the player travels on is pulled by an S1 modeled locomotive.
• In the anime series, the Galaxy Railways, the engine for Vega Platoon, Iron Burger, is loosely based on the S1

See also[link]

• PRR locomotive classification

References[link]

1. ^ ^{a b c} "Raymond Loewy-Locomotives". The Avanti. Archived from the original on 2007-09-27. http://web.archive.org/web/20070927130653/http://www.theavanti.com/locomotives.htm. Retrieved 2007-09-02. 
2. ^ ^{a b} "It's a bird! It's a plane! No, it's - an office tool". The Home Forum > Essays. The Christian Science Monitor. September 23, 2004 edition. http://www.csmonitor.com/2004/0923/p18s02-hfes.html. Retrieved 2007-09-04. 
3. ^ "PRR Chronology 1939" (PDF). PRR Chronology. Pennsylvania Technical and Historical Society. September 2004 Edition. http://www.prrths.com/Hagley/PRR1939%20Aug%2004.wd.pdf. Retrieved 2007-09-02. 
4. ^ ^{a b} "PRR Chronology 1945" (PDF). PRR Chronology. Pennsylvania Technical and Historical Society. September 2004 Edition. http://www.prrths.com/Hagley/PRR1945%20Sep%2004.wd.pdf. Retrieved 2007-09-02. 
5. ^ ^{a b c d e f g h} "Actual Production Models Shown". Brochures. www.lionel.com. 2003. http://www.lionel.com/Brochures/2003_Brochures/penn_s1_duplex/pennsy_s1-duplex_page2.html. Retrieved 2007-09-03. 
6. ^ ^{a b} Reed, Brian (June 1972). Pennsylvania Duplexii. Loco Profile 24. Windsor, Berkshire: Profile Publications Limited. pp. 267–271. 
7. ^ ^{a b} "Milwaukee A class Atlantics cont.". Was German 05 002 The World's Fastest Steam Loco?. www.germansteam.co.uk. Page Added 21 April 2005. http://www.germansteam.co.uk/FastestLoco/fastestloco.html. Retrieved 2007-09-03.