Prototype Deltic


In October 1955 the Traction Division of English Electric unveiled the World’s most powerful diesel locomotive at its Preston works. It was remarkable for several reasons. At 3,300hp it had almost 50% more power than other designs being considered by the nascent BR Modernisation Programme. Not only was it more powerful, it was lighter too, tipping the scales at 106 tons compared with the 140 tons of less powerful rivals.
The phenomenal power to weight ratio of this prototype was derived from changing one element of orthodox diesel locomotive design. Instead of a four stroke diesel engine with cylinders arranged in vertical banks or V formation, a two stroke design with groups of six cylinders arranged in a layout with two opposing pistons per side took its place. The triangular shape formed was reminiscent of the Greek letter Delta and so the prototype was given the name “Deltic”.

The Engine
The “Deltic” did not just spring into life in 1955 as a flash of innovation. It was in fact the logical conclusion of diesel engine development that had started in Germany in the late 1920s at the Junkers aircraft company. The simplicity and low fuel consumption of diesel engines were attractive to anyone developing long range aircraft. The challenge was to produce a design that delivered a good power to weight ratio. By devising the deltic layout, Junkers produced an engine that weighed 2lb per horsepower.
In 1934 the British Napier aero engine company purchased the right to manufacture engines to this design and developed two versions but neither was put into production as Napier concentrated on building petrol engines. In 1942 Mr. George Nelson (later knighted and subsequently ennobled) was asked by the Government to reorganise the Napier works for mass production of their Sabre engine. Mr. Nelson had been Managing Director of the English Electric company since 1930.

During the 1930s, English Electric became established in the diesel electric locomotive business. Shortly after Mr. Nelson arrived at the Napier works, English Electric took over Napiers and Mr. Nelson became its Managing Director.
After the war, the Admiralty approached English Electric with a request for a high powered diesel engine to replace the petrol engines used in its fast patrol boats. English Electric passed the task of development to their subsidiary, Napiers. The result of this development was the Deltic engine, an 18 cylinder opposed piston, two stroke arranged in three banks of six cylinders with a common crankshaft at each corner of the triangle. Every effort was made to keep engine weight down through the use of light alloys. The cylinder arrangement made the unit both compact and very smooth running.
Although the Deltic engine was developed for marine use, the company looked for other ways to recoup the large investment they had made. One area which could benefit from a powerful, lightweight and compact unit was rail traction. George Nelson saw this possibility and signed off the £250,000 private venture that driven by his forceful character culminated in the unveiling of the prototype at Preston in 1955.

The Prototype
The prototype was powered by two Deltic engines which had been derated from 2,500hp to 1,650 hp so as to extend the engine life from 1000hrs to 6000hrs. This was still considerably less than the 10,000 hrs service interval of conventional four strokes. The main reason for this was the Deltics were run at a much higher speed of 1,500 rpm rather than the conventional 850 rpm. There were concerns that the higher idle speed of Deltics might prove too intrusive in enclosed stations.

Preliminary running trials began in November 1955 on the London Midland Region between Euston and Liverpool, mainly on fast freight trains. It was withdrawn from service in early 1956 for minor modifications before returning for a series of performance tests in August and September.
The tests took place between Carlisle and Skipton covering 5,000 miles which more than adequately demonstrated the power of this locomotive. One test involved a train of 20 coaches, grossing 642 tons, being driven at full power over the 15 miles from Ormside to Ais Gill which is mostly 1 in 100.
Following the tests, the Deltic worked passenger services between Euston and Liverpool on named expresses such as the “Merseyside Express” and the “Shamrock”. In January 1957 it worked the London – Carlisle route but by May it was back on Liverpool duties once more. In June the schedule was cranked up so that the locomotive was doing 700 miles a day, six days a week.

In 1961 when the first production units were nearing completion, the prototype Deltic was returned to English Electric’s Vulcan works with over 400,000 miles on the clock. On Sunday 28th April 1963 the prototype was delivered by road to the Science Museum in London. It was subsequently moved to the National Railway Museum in York. When it was introduced, the Deltic was the most powerful diesel locomotive in the world with a ground breaking power to weight ratio.

References: The Deltics. A Symposium. Second revised edition. Cecil J.Allen, G.F.Fiennes, Roger Ford, B.A.Haresnape, Brian Perren. Published by Ian Allan ISBN 0 7110 07993
British Rail Main Line Diesels Compiled S.W.Stevens-Stratten Published Ian Allen ISBN 0 7110 0617 2