Pennsylvania Railroad class S1

Pennsylvania Railroad S1
The official publicity photo of PRR S1 6100 of 1939
Type and origin Power type Steam Builder PRR Altoona Works Serial number Altoona 4341 Build date 1939 Total produced 1
Specifications Configuration: ​  • Whyte 6-4-4-6  • UIC 3′BB3′ Gauge 4 ft 8+1⁄2 in (1,435 mm) Leading dia. 36 in (914 mm) Driver dia. 84 in (2,134 mm) Trailing dia. 42 in (1,067 mm) Wheelbase Coupled: 26 ft 6 in (8.08 m), Loco: 64 ft 4 in (19.61 m), Loco & tender: 123 ft 9+1⁄4 in (37.73 m) Length 140 ft 2+1⁄2 in (42.74 m) Width 10 ft 7 in (3.23 m) Height 16 ft 0 in (4.88 m) Adhesive weight 281,440 lb (127,700 kg; 127.7 t) 1st Driver: 73,800 lb (33,475 kg; 33 t), 2nd Driver: 73,130 lb (33,171 kg; 33 t), 3rd Driver: 66,970 lb (30,377 kg; 30 t), 4th Driver 67,460 lb (30,599 kg; 31 t) Loco weight 608,170 lb (275,861 kilograms; 276 tonnes) Tender weight Empty: 197,020 lb (89,370 kg; 89.37 t); Loaded: 451,840 lb (205,000 kg; 205.0 t) Total weight 1,060,010 lb (480,812 kilograms; 481 tonnes) Tender type 250 P84 16-wheel tender (two 4-axle trucks) Fuel type Coal Fuel capacity 52,900 lb (20,000 kg; 20 t) Water cap. 24,230 US gal (91,700 L; 20,180 imp gal) Firebox: ​  • Grate area 132 sq ft (12.3 m2) Boiler 100 in (2,540 mm) Boiler pressure 300 lbf/in2 (2.07 MPa) Heating surface: ​  • Firebox 660 sq ft (61.3 m2)  • Tubes and flues 219 tubes (2.25 in), 69 flues (5.5 in).  • Total surface 7,746 sq ft (719.6 m2) Superheater: ​  • Heating area 2,085 sq ft (193.7 m2) Cylinders Four Cylinder size 22 in × 26 in (559 mm × 660 mm) Valve gear Walschaerts
Performance figures Maximum speed 152 mph (245 km/h) (Claimed) Operating speed ≤ 120 mph (193 km/h) Power output 7,200 hp when hauling 1,200 tons train at 100 mph (161 km/h) Tractive effort 76,403 lbf (339.86 kN) (at 85% cut-off) or 71,900 lbf (319.83 kN) (at 70.6% cut-off) Factor of adh. 3.68
Career Operators Pennsylvania Railroad Numbers 6100 Retired 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.^[1][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 140 ft 2+1⁄2 in (42.74 m) 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 (76,403 lbf (339.86 kN)) 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.