4-6-6-4 class, original Challenger was designed by Otto Jabelmann of the Union
Pacific and first built by Alco for UP. Approximately 230 Challengers were
built nearly alike, differing only in their steam pressure, cylinders, and
boilers. All Challengers had either 69" or 70" drivers and were
rated at 94,400 pounds tractive effort on the Delaware Hudson to 106,900
pounds tractive effort on the Northern Pacific.
HO - Steam Loco Kits
Union Pacific Challenger 4-6-6-4
All loco kits, tender kits and superdetail kits are sold out and discontinued.
Most parts are available for repairing old locos.
The 4-6-6-4 was often used for
passenger service, but its main function was carrying heavy, fast freight. It
could average speeds of up to 70 miles per hour.
The original Challengers had
21" x 32" cylinders, 69" drivers, 255 pounds steam pressure and
weighed 566,000 pounds.
The original Union Pacific
Challengers were numbered from 3900 to 3939 when they came from Alco, but were
renumbered to 3800 to 3839 in 1944 in order to allow space for use on later
Alco modified the Challenger
starting in 1942 and ending in 1944, making a total of 105 new Challenger
locomotives. These improved locomotives had attached front engines. Springs
and equalizers took up all irregularities in the track to keep the train in
equilibrium. This better balance allowed the new Challengers to reach speeds
of up to 70 miles per hour or more.
Boiler pressure was increased
to 280 pounds, allowing for smaller cylinders. Drivers were still 69",
but the total wheelbase was made 5 1/4" longer. The engine now weighed
627,000 pounds and the tractive effort increased to 97,350 pounds.
The engines were numbered in
three groups, 3950 to 3969, 3975 to 3999, and 3930 to 3949, with the overlap
mentioned earlier above.
Twin stacks were used, large
sandboxes were added, as well as 14-wheel bed type tenders of the centipede
pattern. Elesco exhaust steam injectors were mounted on the left side of some
engines, and were hidden on the inside of others. The pilot was now made of
cast steel, and the boilers were made of Bethloc deoxidized steel boilers,
replacing the original boilers, which were made of manganese.
Some engines that had been originally intended
for the Union Pacific were diverted to the Denver and Rio Grande Western.
These were numbers 3800 to 3805. They did not correspond with other
Challengers made by Baldwin and were sold to Clinchfield. Clinchfield then had
two types of Alco Challengers corresponding to the two types on the Union
here for price Lists