Union Pacific 4-6-6-4 "Challenger" Type Locomotives

Introduction

The Union Pacific Railroad took delivery of the very first locomotive with the 4-6-6-4 wheel arrangement in 1936 when it received 15 of them from the American Locomotive Company. These newly named "Challengers" were designated Class CSA-1.

In 1937, another 25 ALCO-built "Challengers" were added to the roster. This group, designated Class CSA-2, was given road numbers 3915 through 3939. They were similar to the Class CSA-1s. Six of them, numbers 3934 through 3939, were equipped for passenger service.

In 1942, ALCO delivered 20 Class 4664-3 "Challengers" which were numbered 3950 through 3969. The tenders on these locomotives were larger than either of the CSA classes.

In 1943, another 25 Class 4664-4 "Challengers" came from ALCO and were numbered 3975 through 3999. This group was very similar to the Class 4664-3s except that each weighed 6,500 pounds more.

A final 20 ALCO-built "Challengers" arrived in 1944 giving the Union Pacific a total of 105 of the 4-6-6-4s. These locomotives designated Class 4664-5 were similar to the Class 4664-3s except for an additional 7,500 pounds in the total weight. They were numbered 3930 through 3949 which required that the Class CSA-1 and CSA-2 locomotives be renumbered into the 3800 series.

An article by King in "Trains" in the early 2000s stated that the later UP Challengers cost around $130,000.00.

There are two surviving Union Pacific Class 4664-4 "Challengers", number 3977 at Cody Park in North Platte, NE and number 3985 which is operational and used in excursion service by the Union Pacific.

Roster by Richard Duley

ClassQty.Road NumberLater NumbersYear Built Builder Notes
CSA-1153900-39143800-38141936ALCO1
CSA-2193915-39333815-38331937ALCO2
CSA-2 63934-39393834-38391937ALCO3
4664-3203950-39691942ALCO4
4664-4253975-39991943ALCO5
4664-5203930-39491944ALCO6

Please see this page for more details on UP Challenger renumbering, coal versus oil burners, paint schemes, and other details on the various classes of UP Challengers.

Notes
  1. Delivered with road numbers 3900-3914 and renumbered 3800-3814 in 1944. Converted to oil burners in 1943. Numbers 3801, 3802, 3804, 3807, 3809, 3811 & 3814 were converted to burn coal in 1950 and renumbered in the 3700 series and later that same year converted back to burn oil and retuned to the 3800 series numbers. Numbers 3800-3814 scrapped between 1956 and 1961.
  2. Delivered with road numbers 3915-3933 and renumbered 3815-3833 in 1944. Number 3915 converted to burn oil in 1942. Numbers 3817 & 3818 converted to burn coal in 1950 and renumbered in the 3700 series and later that same year converted back to burn oil and returned to the 3800 series numbers. Numbers 3815-3833 scrapped between 1956 and 1960.
  3. Delivered with road numbers 3934-3939 and renumbered 3834-3839 in 1944. Numbers 3934-3939 delivered equipped for passenger service and converted to burn oil in 1937. Numbers 3934-3939 scrapped between 1956 and 1960.
  4. Numbers 3950-3969 scrapped between 1956 and 1961.
  5. Numbers 3975-3984 converted to burn oil and renumbered 3708-3717 in 1952. Numbers 3975-3999 scrapped between 1959 and 1961.
  6. Numbers 3930-3932, 3934, 3937, 3938, 3943 & 3944 were converted to burn oil and renumbered 3700-3707 in 1952. All scrapped between 1952 and 1960.

Class Details by Steve Llanso

Class 4664-3/4 (Locobase 341)

Firebox heating surface included 81 sq ft in circulators. These Challengers were revised from the earlier CSAs by Otto Jabelman with smaller pistons, larger grates, and higher boiler pressures. The table data is for class 4664-3 (3950-3969). (Thanks to Chris Hohl for querying the class ID and road numbers for this class.) See Raymond Gutierrez's renumbering of the UP 4-6-6-4s at Wes Barris's http://www.steamlocomotive.com/challenger/renumbering.php for the complicated details.

The 60 later engines in the UP's run of 16-axle articulateds were not designated by the UP as Challengers, but simply 4664-3 through 4664-5. The 4664-3s were numbered 3950-3969 from the start and never changed (except for 3968, which was converted to oil-burning in 1946 and renumbered 3944.

The 4664-4s were delivered as coal burners and numbered 3975-3999. The first ten were renumbered 3815-3824 in 1944, regained their original numbers in 1945 when they were converted to oil-burning, were coal-burners in 1946, converted again to oil-burning in 1949, and renumbered 3708-3717 in 1952. They were scrapped in 1959-1960 with their original numbers assigned.

The 3975-3999 remained coal burners throughout their careers. 3985-3993 were renumbered 3825-3833 in 1944, but took back their original numbers later, probably in 1946.

The -3 and -4 designs were fitted with a vertical hinge between the driving units so positioned as to even the weight distribution between the front and rear driver sets. These engines could run at 70 mph pulling a 20-car passenger train. See Locobase 338 for a description of the revised bearing design that permitted smooth riding at such speeds.

Six more locomotives of identical design were leased as #3800-3805 for the Denver and Rio Grande Western in 1943, which returned them in 1946. At this point they went to the Clinchfield as E-3 (670-675) and retired in 1953.

Class 4664-5 (Locobase 6613)

Data from 1946 Union Pacific Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive collection.

When the UP ordered more 4-6-6-4s in 1944, they took the opportunity to substantially rework the boiler of the 1930s variants described in Locobase 1406. Hoping to confuse future compilers of steam locomotive information, the railroad renumbered the last ten locomotives of its earlier CSA-2 class and reused the original 3930-3939 for the first ten of this 1944 class.

The tubes were shortened by 2 feet, 94 sq ft (8.7 sq m) of circulators were added to the firebox heating surface, the grate area jumped by 24 sq ft (2.2 sq m), superheater area increased by 91 sq ft (8.4 sq m), boiler pressure rose by 25 psi (1.72 bar), cylinder diameter shrank by an inch ....about all that didn't change was the driver diameter.

See Locobase 338 for a description of the revised bearing design that permitted smooth riding at high speeds.

Class CSA-1/CSA-2 (Locobase 1406)

Data from Union Pacific 11 - 1946 Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive collection. This group of 40 were first numbered 3900-3939, but later renumbered 3800-3839.

Union Pacific's general mechanical engineer Arthur H. Fetters suggested basing a simple articulated design on the big 9000-series 4-12-2, thus invented the Challenger wheel arrangement. See Locobase 338 for a description of the revised bearing design adopted in 1940 that permitted smooth riding at higher speeds. But Alfred Bruce's summary of Challenger capabilities can be applied to all 4-6-6-4s. Locomotives with this wheel arrangement were, he said, "...of a size that could be handled without too much difficulty, was well balanced and accessible, and had adequate ashpan capacity. In addition, it had all modern improvements, including integral cast-steel bed frames and roller bearings on all axles." (The Steam Locomotive in America, 1952, p. 328.)

UP eventually bought 105 4-6-6-4 locomotives for express passenger and freight service. See Locobases 331 and 6613

According to the locomotive diagram, the first 10 had Worthington feedwater heaters, then next 5 had Sellers had exhaust steam injectors, and the last 25 Worthingtons. This latter group arrived in 1937. They also put 5 more tons of adhesion weight, bulking up to 407,340 lb and increasing overall engine weight to 584,950 lb.


Specifications by Steve Llanso
Class4664-3/44664-5CSA-1/CSA-2
Locobase ID341 6613 1406
RailroadUnion Pacific (UP)Union Pacific (UP)Union Pacific (UP)
CountryUSAUSAUSA
Whyte4-6-6-44-6-6-44-6-6-4
Road Numbers3950-3969, 3975-39993930-39493900-3939 / 3800-3839
GaugeStdStdStd
BuilderAlcoAlcoAlco
Year194219441936
Valve GearWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase12.17'12.17'12.17'
Engine Wheelbase60.37'35.08'35.08'
Ratio of driving wheelbase to overall engine wheebase 0.20 0.35 0.35
Overall Wheelbase (engine & tender)106.67'106.67'97.87'
Axle Loading (Maximum Weight per Axle)
Weight on Drivers403700 lbs404200 lbs399840 lbs
Engine Weight627000 lbs634500 lbs566950 lbs
Tender Light Weight436500 lbs434500 lbs322600 lbs
Total Engine and Tender Weight1063500 lbs1069000 lbs889550 lbs
Tender Water Capacity25000 gals25000 gals18106 gals
Tender Fuel Capacity (oil/coal)28 tons28 tons6000 gals
Minimum weight of rail (calculated) on which locomotive could run112 lb/yard112 lb/yard111 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter69"69"69"
Boiler Pressure280 psi280 psi255 psi
Cylinders (dia x stroke)21" x 32" (4)21" x 32" (4)22" x 32" (4)
Tractive Effort97352 lbs97352 lbs97305 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.15 4.15 4.11
Heating Ability
Firebox Area602 sq. ft604 sq. ft548 sq. ft
Grate Area132 sq. ft132 sq. ft108.25 sq. ft
Evaporative Heating Surface4817 sq. ft4642 sq. ft5304 sq. ft
Superheating Surface2355 sq. ft1741 sq. ft1650 sq. ft
Combined Heating Surface7172 sq. ft6383 sq. ft6954 sq. ft
Evaporative Heating Surface/Cylinder Volume187.75180.93188.37
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation369603696027604
Same as above plus superheater percentage491574693934229
Same as above but substitute firebox area for grate area224185214782173278
Power L1364242928223843
Power MT1193.48958.27788.79

Photos

Reference

Credits

Introduction and roster provided by Richard Duley. Class details and specifications provided by Steve Llanso of Sweat House Media.