PROTOTYPE INFO:

   The Union Pacific Challengers were a type of simple articulated 4-6-6-4 steam locomotive built by American Locomotive Company for the Union Pacific Railroad. 105 of these locomotives were built between 1936 and 1943. The Challengers were nearly 122 ft (37 m) long and weighed 284,800 kg. 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 locomotives were built specifically for Union Pacific and much of the experience gained later went into the design of the “Big Boy”.

   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 six driving wheels is driven by two steam cylinders. In essence, the result is two engines under one boiler. The Union Pacific Railroad sponsored development of this type to meet the need for higher speeds in main-line service. Historically, articulated locomotives had been limited to slow speeds by factors inherent in their design. The technical breakthroughs achieved with the Challenger enabled the carrier to develop the Big Boy with the same speed expectations. Speeds in excess of 60 M.P.H., while unheard-of on other railroads using articulated steam locomotives, became commonplace on the Union Pacific.
   The 105 were divided into five orders, which can be put into two groups: the first two orders of “original” also known as “light” Challengers, and the final three of “heavy” Challengers. The “Heavy” Challengers are currently available in stock.

Key Features

    Boiler backhead with printed manual controls
    Individually applied piping, valves, generators, etc.
    Correctly operating eccentric cranks
    Adjustable cab roof vent
    Headlights and number boards with directional light change
    Tender light
    Genesis Five pole, skewed armature motor with two flywheels
    Pivoting front and rear engines for negotiating 18" radius curves
    Current pick-up on all driver and tender wheels
    8-pin connector plug between loco and tender