EMD SD50

The EMD SD50 is a 3500 hp diesel-electric locomotive built by General Motors Electro-Motive Division. It was introduced in May 1981 as part of EMD's "50 Series", but prototype SD50S locomotives were built from 1980; production ceased in January 1986. The SD50 was in many respects a transitional model between EMD's Dash 2 series which was produced throughout the 1970s and the microprocessor-equipped SD60 and SD70 locomotives.

History
The SD50 was produced in response to increasingly tough competition from GE Transportation Systems, whose Dash 7 line was proving quite successful with railroads. While EMD's SD40-2 was a reliable and trusted product, GE's line included locomotives up to 3600 hp with more modern technology, as well as very competitive finance and maintenance deals. EMD responded throughout the SD50 program by offering discounts on large orders.

GM-EMD had previously produced 3600 hp locomotives, the SD45 and later SD45-2, but these used huge, 20-cylinder engines with high fuel consumption, and had reliability problems when first introduced. Demand for the 45 series dropped sharply after the 1970s fuel crisis. The SD50 used an updated version of the V16 645 used in the SD40-2, uprated to 3500 hp- and later 3600 hp - at 950 rpm from 3000 hp at 900 rpm. This proved to be a step too far; the 50 series models were plagued by engine and electrical system problems which harmed both sales and the reputation of EMD.

The subsequent SD60 model replaced the overstressed 950-rpm 645F engine with a new engine series, the 900-rpm 710G.

The SD50's long hood saw changes from previous EMD models. The overall frame length was increased, and the long hood was made substantially longer. The resistors for the dynamic brake grid were moved from their previous location above the prime mover to a new, cooler location in front of the engine compartment air intakes, where they were more effectively separated from the rest of the locomotives' systems, and also closer to the locomotive's electrical switchgear, thereby simplifying the prime mover maintenance procedures, and the electrical system as well.

Technical
The SD50 is powered by V16 16-645F3 series diesel engine driving either an EMD AR11A-D14 or an EMD AR16A-D18 traction alternator. The power generated by the traction alternator drove 6 EMD D87 traction motors rated at 1170 amps each.

Depending on customer options, the SD50 was available with a multitude of traction-motor gearing ratio and wheel size options, the most common of which being the 70:17 ratio with 40 in wheels, this allowed for a top speed of 70 mph. Other gearing options for the SD50 with 40 in wheels include 69:18 for 76 mph, 67:19 for 82 mph and 66:20 for 88 mph. 42 in wheels were also available. Customers of the SD50 also had the option of either HT-C trucks (identified with a hydraulic shock on the side of the middle axle of each truck) or the earlier Flexicoil trucks, which only Conrail opted for. Some investigators implicated the HT-C truck in derailments in Amtrak's SDP40F locomotive fleet and Conrail chose to order SD40-2s and their first order of SD50s with the earlier Flexicoil C truck. The controversy surrounding the HT-C truck was eventually disproved, and Conrail's second order of SD50s as well as their SD60 variants were all HT-C equipped.

The SD50 could be equipped with fuel tanks sizes from 3200 usgal up to 4400 usgal, had a lube oil capacity of 396 usgal and a cooling water capacity of 276 usgal.

SD50S
The SD50S ("short frame") were prototype units built in December 1980. They were shorter than production locomotives by approximately 2 ft. There were 6 SD50S built, and all of these prototypes were sold to the Norfolk & Western and passed to the Norfolk Southern; they were withdrawn in the early 2000s as non-standard. Two were rebuilt in 2008 as "SD40E" models by Norfolk Southern's Juniata Shops, along with several standard length SD50's.

The designation also applies to five locomotives built by EMD Australian licensee Clyde Engineering, Adelaide for Hamersley Iron. These were shorter than production SD50s, and were equipped with a special double cab roof for insulation against the hot Australian desert sun in the Pilbara region. Withdrawn in November 1995, they were sold to National Railway Equipment Company and exported to the U.S. in February 1999 and used in national lease service. They were subsequently sold to the Utah Railway in June 2001, where they remain.

SD50F
The SD50F was a Canadian cowl unit version equipped with a "Draper taper" (inset section aft of cab for limited rear visibility). 60 were built for the Canadian National Railway as road numbers 5400-5459. Early engine problems resulted in a temporary down-rating to 3300 hp. Eventually the units were re-rated to 3500 hp; however, like their U.S. cousins, they continued to suffer from relatively low reliability, frequently suffering engine, power assembly, and crankshaft failures.

Out of the 60, only six of these locomotives are known to exist today, with the rest of the fleet scrapped.

Current owners
As of 2008, current owners and operators include:
 * CN: All CN SD50Fs were retired by the end of October 2008.
 * CSXT: inherited SD50s from the B&O, C&O, Conrail (split with NS), and Seaboard System; 25 ex-CR units assigned to MofW service, with 8 remaining in regular service; all units except for 8507, 8514, 8520, 8522, 8525, 8526, 8532, 8540, 8550-8552, 8566, 8568, 8586, 8596, 8624, 8629, 8635, and 8641 have been de-rated to 3000 hp and re-designated as SD50-2s; the remaining ones will be "dash-twoed" in the future. 8502, 8523, 8526, 8536, 8540, 8568, 8582, 8604, 8609, 8612, 8613, 8614, 8619, & 8662 have been rebuilt into SD50-3's.
 * Dakota, Missouri Valley and Western Railroad acquired CN 5404 which was located at the Rosser Street Shops in Bismarck, ND on 31 May 2009
 * Helm Financial: lease operator owning ex-UP (née CNW) SD50s; 6 ex-CN SD50Fs have recently been acquired.
 * Hudson Bay Railway, which is owned by OmniTRAX: 10 ex-UP (née-MP) SD50s
 * Kansas City Southern: 9 SD50s it originally purchased and 25 ex-NS (née-CR) & CSXT (née-CR) SD50s.
 * National Railway Equipment: operates 44 ex-NS & CSXT (née-Conrail) SD50s. Ex-NS 5473 (nee CR 6829) wrecked in 2006 and scrapped.
 * Norfolk Southern: Retains 4 of 26 SD50s it purchased and 46 ex-Conrail units. Several former SD50s have been rebuilt into SD40Es. 4 of the 6 SD50Ss have been retired, but 2 have been rebuilt into SD40Es.
 * Reading, Blue Mountain & Northern: 6 units purchased from UP. 4 units purchased from CSXT in early 2019.
 * Southwestern Railroad: 2 ex-UP (née-DRGW) SD50s. Ex-UP 9851 (former DRGW 5507) wrecked in 2015 and scrapped.
 * Union Pacific: inherited 60 SD50s from Missouri Pacific, 35 from Chicago & North Western, and 17 from DRGW via Southern Pacific. Some are still in service but are rarely used for mainline use.
 * Utah Railway: 5 ex Hamersley Iron SD50Ss
 * Watco Companies: 18 ex-UP (née-CNW) and 2 ex-NS (née-Conrail) SD50s

Rebuilds
A number of SD50s have been rebuilt into the equivalent of SD40-2s. The Dash 2 features are already contained within the SD50. The units are re-rated from 3500 hp at 950 rpm to 3000 hp at 900 rpm. This is actually a quite simple change to the locomotive's Woodward PGE engine governor.