The British Rail Class 52 was a class of 74 Type 4 diesel-hydraulic locomotives built for the Western Region of British Railways between 1961 and 1964. All were given two-word names, the first word being "Western" and thus the type became known as Westerns.
Historical Context[]
When switching to diesel traction as part of the Modernisation Plan of the 1950s, British Railways (BR) designed, and commissioned designs for, a large number of locomotive types. At this time BR's regions had a high degree of autonomy, which extended as far as classes of locomotives ordered and even the design criteria for those locomotives. Whilst almost all other diesel locomotives were diesel-electric, the Western Region employed a policy of using diesel-hydraulic traction, originally commissioning three classes of main line locomotives: a type 2 and two type 4s (later designations class 22, class 41 and class 42). With pressure to increase the speed of the transition from steam to diesel, volume orders for the class 22 and class 42 (along with a similar design class 43) followed in 1957, a mere two years after the original orders and well before any idea of performance or reliability could be gained. At the same time it was realised that all the existing orders (diesel-electric and diesel-hydraulic) were for types 1, 2 and 4; thus orders were placed for 101 Type 3 diesel-hydraulics (later Class 35). However the increasing demands for more powerful locomotives prompted a further order, in 1961, for 74 diesel-hydraulics of 2,700 hp (2,000 kW); so when the first locomotive was outshopped from Swindon Works in December 1961, less than a year after the order was placed, the Westerns were born.
The theoretical advantage of diesel-hydraulic was simple: it resulted in a lighter locomotive than equivalent diesel-electric transmission. This provided a better power/weight ratio and decreased track wear. Unfortunately, it had several key disadvantages:
- The technology was proven in continental Europe, particularly Germany, but was new to the UK. At the time, it was considered politically unacceptable for the UK government to order railway rolling stock from foreign companies, especially German companies so soon after the Second World War. This resulted in most of the engines and transmissions being manufactured in the United Kingdom under licence from the German manufacturers.
- The most robust hydraulic transmissions were only capable of handling engines with power output of around 1500 hp (1120 kW); to build a more powerful locomotive would involve two diesel engines and two transmissions.
- The transmission had significantly higher power losses than diesel-electric, negating some of the benefits and resulting in considerably higher fuel consumption.[citation needed]
Experience showed that the Bristol-Siddeley-Maybach engines were superior to those made by North British Locomotive Company-MAN and although the use of twin engines in the same locomotive was new, the design did not produce any insurmountable problems. In the end the diesel-hydraulic experiment foundered on low fleet numbers, poor maintenance conditions and design issues; not on its German heritage or development of a novel configuration. BR's Swindon Works maintained all the diesel-hydraulic locomotives, and their early demise resulted in a much reduced workload and hastened its eventual closure in 1986
The Western[]
With the Hymeks and Warships already in service but proving underpowered for top-link services, BR Western Region needed a high-powered locomotive for these trains – the Western therefore needed two diesel engines to achieve the required power output. In keeping with their policy, a new locomotive with a hydraulic transmission was envisaged. Experience had shown that the Maybach engines in the Hymeks were superior to the earlier Maybach and MAN engines used in the Warships, particularly in power output. Also Maybach were able to offer their 12 MD engines rated at 1,350 bhp (1,010 kW) allied to a Voith transmission; a Mekydro transmission designed to handle such power could not be fitted into the British loading gauge.
Prototypes sited the engines behind the driving cabs but drivers found this too noisy; moving the engines centrally meant making the locomotive heavier, removing some of the design's advantage. In production use, the dual-engine arrangement turned out to have some advantages: in particular, the Westerns were able to continue operating with a single engine running in situations where more conventional single-engine designs would require rescue by another locomotive.
The most serious continual problem with the class was the design fault mismatch between the Maybach MD655 engines and the Voith L630rV three speed hydraulic transmissions. The top gear ratio in the transmission was too high for the torque characteristics of the engine: the result was that a single locomotive could struggle to reach its claimed 90 mph (140 km/h) top speed in the absence of down grades, more so when work-weary and due for overhaul. These factors, combined with the South Devon Banks (a major part of their running grounds) deleterious effect on tired engines, all conspired against the Westerns continuing in top-line service. With fifty Class 50 locomotives becoming available, following completion of the West Coast Main Line electrification, and new High Speed Trains, the speed and comfort increases the Western Region sought could be achieved and the Westerns dispensed with. Towards the end of their careers the Westerns were all allocated to Laira (Plymouth).
Competition and Comfort[]
Whilst the design was largely successful, the working life of the class was relatively short. Its non-standard design added to its maintenance costs while the national British Rail policy was moving away from diesel-hydraulics. When the Westerns were introduced in 1962, the Western Region had 226 diesel-hydraulics and 10 diesel-electrics (excluding shunters); by 1966 the numbers were 345 and 269 respectively. As a result, the early 1970s saw the decision taken to retire all the diesel-hydraulic types. Class 46 and Class 47 took over passenger and heavy freight while Class 25 covered the lighter duties. Following completion of the electrification of the West Coast Main Line throughout from London to Glasgow, the Class 50s were reallocated to the Western Region; the introduction of High Speed Trains three years later was the final nail in the coffin for the Class 52 Westerns.
In 1968–69 the Westerns received train air brake equipment in addition to their vacuum exhausters, thus significantly extending their working lives, unlike the similar but lower-powered, Warship class, although four of the class (D1017–D1020) did not receive dual brakes, with these locomotives being among the first withdrawals. The vacuum brake equipment was retained and to fit the additional equipment, it was necessary to remove one of the fuel tanks. However, as with the Warships, it proved impossible to equip them with electric train heating (ETH, or head-end power in US terminology). The Western Region faced particularly stiff competition for its prime inter-city services in the mid to late 1970s from the M4 motorway and it was generally felt within BR that a significant speed and comfort increase on the prime London Paddington-Bristol route were necessary. The lack of ETH meant the Westerns could not power the newly introduced air-conditioned BR Mark 2d/e/f coaches – a shortcoming that classes 47 and 50, equipped with ETH (the latter from new), did not share.
Performance[]
The highest recorded speed with a Western that O. S. Nock was aware of was 102 mph (164 km/h) when D1068 hauled nine coaches (305 tons gross) down 1 in 1320 (i.e. virtually level) at Southall. The train averaged exactly 100 mph (161 km/h) for 12.8 miles (20.6 km) between Slough and Ealing whilst hauling a service from Reading to Paddington. An unverified eyewitness account by a BR secondman stated that 110 mph (177 km/h) had been achieved when his driver drove a Western between Reading and Westbury. He experienced the locomotive shaking from side to side as 110 mph was indicated on the speedometer.[citation needed]
However, when it came to drawbar horsepower the Westerns in some respects were less capable than the equivalent diesel electric locomotives. Nock states "whilst the Westerns took their rightful place as fast and powerful locomotives it became evident that they were showing the same deficiency in actual power put forth at the drawbar as the [diesel-hydraulic] Warships had done. The highest output that came to my notice was a sustained 85 mph (137 km/h) hauling 560 tons descending 1 in 1320, which equates to 1500 edhp (equivalent drawbar horsepower)". This is 56% of power at the flywheel, whereas for a diesel-electric one would normally expect a figure of 75 to 80%.[citation needed] A similar result was obtained when Clough & Beckett compared the performance of type 4 diesel locomotives (Classes 45/46/47/50/52) hauling trains up the ascent to Whiteball summit. They deliberately chose data to show each class in their best light and included a Western run which produced 1775 edhp but they still concluded that "without doubt the Westerns get the wooden spoon; certainly not what one would expect from units of 2700 bhp". The best performer was the Class 50, a 2,700 hp (2,000 kW) diesel-electric locomotive: on one run this achieved 2115 edhp.
Despite this apparent limitation, the BR Western Region load-limit book gave the same 550 ton loading figure for both the Class 52 and Class 47 diesels over the South Devon banks between Newton Abbot and Plymouth. The reason for this is that, while the diesel-electric classes could produce high maximum tractive effort for limited periods, diesel hydraulics could produce significantly higher continuous tractive effort.
Preservation[]
Of the 74 locomotives that were built, 7 have survived into preservation at various heritage railways.
Gallery[]
_(6137384220).jpg "No.D1048 Western Lady (Class 52) (6137384220).jpg (232 KB)")
