BR Class 56 Diesels

By the 1970s it was obvious the traction demands of the freight and passenger business could not be met my a single locomotive type. The passenger business sought increased train speeds, but increasing a locomotives' maximum speed, which defines the gear ratio between traction motors and wheels to prevent the motors overspeeding, also increases the minimum speed at which full engine power can be absorbed by the motors. Already the standard Brush type 4 or class 47 fleet was suffering, the 95mph maximum speed being too low to accelerate passenger services further while in heavy freight service electrical damage due to overloading of the generators and motors occurred far too frequently.
Several design studies were conducted, resulting in the InterCity 125 High Speed Train for passenger services and initial plans called for a twin-engined freight locomotive using the same Paxman Valenta 'power packs'. However British Rail engineers have long favoured the use of a single power unit, which usually proves more economical in both fuel and maintenance. The familiar English Electric 16CSVT engine now being offered by the GEC group with a traction rating of 3,250bhp under the Ruston name and class 47 47046 which had recently suffered severe bodyshell damage in a derailment was rebuilt to test this engine, allied with an alternator and solid-state rectifiers in place of the older technology generator in service.

The production design class 56 by BREL used the standard cab design styling, looking very similar to the class 47, though the 56 was instantly recognisable by the horn grille in the cab front in place of the train headcode boxes of the earlier design. The body side was quite plain, excepting an enlarged radiator area, needed to ensure the higher horsepower engine was kept cool while the cantrail line carried air intakes closer to the English Electric style. Below the body the trucks were new and complex-looking, featuring pedestal suspension for each axle with the inner springs linked through equalizer beams to keep all 12 wheels loaded.
Inside the 3,250bhp Ruston 16RK3CT engine drove a Brush alternator powering Brush traction motors geared for a maximum speed of 80mph, allowing use on faster Freightliner trains. At the other end of the scale this gave a minimum continuous rated speed of 16.8mph, compared to the 47s 26mph and the slow speed control system was fitted as standard for use with the automatic loading and unloading MGR power station coal services.

Class 56 numbers rose steadily over the 8-year building programme, with 56001 to 56030 being constructed by Electroputere in Romania, followed by 56031 to 56115 built at Doncaster and the final group 56116 to 56135 built at Crewe. The type quickly proved to be strong and capable locomotives, well suited to heavy general and block train freight services but the class has not been without issues, general reliability of individual locomotives being particularly disappointing at times, the class was a useful addition to the British motive power fleet and a good availability rate usually ensured all rostered duties were covered.
Excepting the unique 56042 which rode on trucks which were a pre-production development design for the class 58 locomotives and was withdrawn in 1991 the entire class passed into EWS ownership at privatisation. Slowly displaced by the new EMD class 66 locomotives in EWS service many class 56s found new owners and operators in the UK and mainland Europe with around 30 examples operational (3 in Hungary).