Union Pacific Challenger

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Union Pacific Challenger
UP 3985 running through Alton, Iowa in October 2008
Power typeSteam
BuilderAmerican Locomotive Company (ALCO)
Build date1936-1943
Configuration4-6-6-4
UIC classification(2′C)C2′ h4
Gauge4 ft 8 12 in (1,435 mm)
Driver diameter69 in (1,753 mm)
Wheelbase60 ft 4 12 in (18.402 m) Engine
121 ft 10 78 in (37.157 m) Engine + tender
Weight on drivers404,000 lb (183.3 t)
Locomotive weight627,900 lb (284,800 kg)
Tender weight446,000 lb (202,000 kg)
Locomotive & tender
combined weight
1,073,900 lb (487,100 kg)
Fuel typeCoal, UP 3985 converted to No. 5 fuel oil
Fuel capacity32 short tons (29 t)
6,450 US gal (24,400 l; 5,370 imp gal) UP3985
Water capacity25,000 US gal (95,000 l; 21,000 imp gal)
Boiler pressure280 lbf/in² (1.93 MPa)
Heating surface:
Tubes
527 sq ft (49.0 m2)
Heating surface:
Flues
3,687 sq ft (342.5 m2)
Heating surface:
Firebox
500 sq ft (46 m2)
Heating surface:
Total
4,795 sq ft (445.5 m2)
Superheater area2,162 sq ft (200.9 m2)
CylindersFour
Cylinder size21 × 32 in (533 × 813 mm)
Top speed70 mph (110 km/h)
Tractive effort97,350 lbf (433.03 kN)
CareerUnion Pacific Railroad
Class4664-4
Number in class105
 
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Union Pacific Challenger
UP 3985 running through Alton, Iowa in October 2008
Power typeSteam
BuilderAmerican Locomotive Company (ALCO)
Build date1936-1943
Configuration4-6-6-4
UIC classification(2′C)C2′ h4
Gauge4 ft 8 12 in (1,435 mm)
Driver diameter69 in (1,753 mm)
Wheelbase60 ft 4 12 in (18.402 m) Engine
121 ft 10 78 in (37.157 m) Engine + tender
Weight on drivers404,000 lb (183.3 t)
Locomotive weight627,900 lb (284,800 kg)
Tender weight446,000 lb (202,000 kg)
Locomotive & tender
combined weight
1,073,900 lb (487,100 kg)
Fuel typeCoal, UP 3985 converted to No. 5 fuel oil
Fuel capacity32 short tons (29 t)
6,450 US gal (24,400 l; 5,370 imp gal) UP3985
Water capacity25,000 US gal (95,000 l; 21,000 imp gal)
Boiler pressure280 lbf/in² (1.93 MPa)
Heating surface:
Tubes
527 sq ft (49.0 m2)
Heating surface:
Flues
3,687 sq ft (342.5 m2)
Heating surface:
Firebox
500 sq ft (46 m2)
Heating surface:
Total
4,795 sq ft (445.5 m2)
Superheater area2,162 sq ft (200.9 m2)
CylindersFour
Cylinder size21 × 32 in (533 × 813 mm)
Top speed70 mph (110 km/h)
Tractive effort97,350 lbf (433.03 kN)
CareerUnion Pacific Railroad
Class4664-4
Number in class105

Built between 1936 and 1943, the Challengers were nearly 122 feet long and weighed more than one million pounds. Articulated like their big brother, the Union Pacific Big Boy, the Challengers had a 4-6-6-4 wheel arrangement. They operated over most of the Union Pacific system, primarily in freight service, but a few were assigned to passenger trains operating through mountain territory to California and Oregon. The 105 locomotives were built specifically by ALCO for Union Pacific having drawn on much of the Big Boy's experience.

The name Challenger was given to steam locomotives with a 4-6-6-4 wheel arrangement. This means that they have four wheels in the leading "pilot" truck, which helps guide the locomotive into curves; two sets of six "driving" wheels, and finally, four "trailing" wheels, which support the rear of the engine and its massive firebox. Each set of driving wheels has its own steam cylinder. In essence, the result is two engines under one boiler.

Two examples survive today: Union Pacific 3985, used for excursion services by Union Pacific and Union Pacific 3977, on static display in North Platte, NE.

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