EMD SD50

The EMD SD50 was introduced in May 1981 as part of General Motors Electro-Motive Division's "50 Series," a line of locomotives developed in direct response to growing competitive pressure from General Electric's Dash 7 locomotives, which were winning customers with higher horsepower ratings and modern technology. EMD's workhorse SD40-2 remained a respected product, but the market demanded greater power output, and the SD50 was designed to answer that need by extracting more performance from the proven 16-cylinder 645 engine rather than returning to the large, fuel-hungry 20-cylinder powerplants used in the earlier SD45 series. That series had fallen out of favor following the fuel crises of the 1970s, and EMD was determined to offer competitive horsepower through a more economical configuration. Despite its sound mechanical heritage, the SD50 earned a troubled reputation in service. The engine and electrical systems proved difficult to operate reliably at the elevated power output demanded of the 645 series engine in this application, and railroads experienced recurring failures that damaged EMD's standing with customers during a period when it could ill afford to lose ground to GE. The locomotive was something of a transitional design, lacking the microprocessor-based control systems that would become standard on the subsequent SD60 and SD70 families. Approximately 370 standard cab units were built for the North American market between 1981 and 1985, with additional variants produced for Canada and export customers. Production came to an end in early 1986. The SD50's legacy is largely defined by its role as a bridge between two eras in EMD's history. Its shortcomings accelerated the development of more sophisticated successor models and underscored the importance of electronic controls in managing high-output prime movers. A number of SD50s were later rebuilt to SD40-2 equivalents by derated to 3,000 horsepower, reflecting the difficulties operators experienced at the higher power setting. Variants included the Canadian SD50F built for Canadian National Railway with a distinctive cowl body and Draper taper, the short-frame SD50S prototypes delivered to Norfolk and Western, and the export-oriented SDL50 built for the Saudi Government Railways Organization.

The SD50 rides on a C-C wheel arrangement, with two three-axle trucks supporting a frame that was noticeably longer than those of its immediate predecessors in the EMD line. Power comes from the EMD 16-645F3B prime mover, a 16-cylinder two-stroke diesel engine producing 3,500 horsepower at 950 revolutions per minute. This engine drives a traction alternator that in turn supplies current to six EMD D87 DC traction motors, one per axle, rated at 1,170 amperes each. The most common gearing arrangement paired a 70:17 ratio with 40-inch wheels, yielding a top speed of 70 miles per hour, though several other gear ratios were available for operators requiring higher speed capability. Trucks were offered in two configurations: the HT-C design and the earlier Flexicoil type, with Conrail notably selecting Flexicoil trucks for its initial SD50 order before later switching to HT-C for subsequent purchases. One notable design change from earlier EMD road units was the relocation of the dynamic brake resistor grids away from their traditional position above the prime mover to a new location forward of the engine compartment air intakes. This placement reduced heat interaction between the braking resistors and other locomotive systems and was intended to simplify maintenance access. Despite this thoughtful engineering refinement, the overall 50 Series platform struggled with reliability in everyday railroad service, particularly as EMD pushed the 645 engine to its practical limits. The combination of higher rotational speed and increased fuel delivery that produced the 3,500 horsepower rating proved difficult to sustain without recurring mechanical issues, a problem that would not be fully resolved until the introduction of the electronically controlled SD60.

Models by: Atlas