The DeItics, or rather the 22 locomotives originally designated English Electric Type 5 Co-Co diesel-electric, over a working life of more than twenty years became top favourites with all rail enthusiasts as they carried out the express passenger duties on the East Coast Main Line. And yet, initially, the design was not in tended for the Eastern Region at all, but the London Midland. Following the highly successful operation of the prototype Deltic locomotive, on LMR and ER metals, it was decided to place an order with English Electric for a production version. In essence this retained the twin I8-cylinder ‘Deltic’ engines of the prototype in a stretched body, with a number of other detail modifications, providing BR with what was at the time the world’s most powerful single unit diesel locomotive.

The first three production Deltics appeared in March 1961 and were allocated to the Scottish, Eastern and North Eastern Regions respectively. They were numbered D9000-02 in the then current numbering scheme. They were the result of six years running experience with the prototype; which remained the property of English Electric until its withdrawal and preservation in the Science Museum in 1963. The prototype had experienced only minor problems during the 400,000miles it covered in service, almost all of which centred around the Napier ‘Deltic’ engine. It was in this, in fact, that the unique nature of the Deltic locomotive was contained. The power unit was developed from a design prepared for the Admiralty in the early 1950s for its ‘Dark’ class fast patrol boats – a lightweight two-stroke diesel, opposed piston, water cooled engine. The cylinders-eighteen in all – were arranged in banks of six around the three sides of an inverted triangle – hence the Deltic name. Happily, the engines installed in the rail version had a much more successful career than those for the Royal Navy.

The genesis of the ‘Deltic’ design was outlined in some draft notes on English Electric’s history prepared for GEC Traction’s publicity department around 1970, and included this summary:

1952

“The development of a completely new ultra lightweight high speed 2-stroke diesel engine by D. Napier & Son, initiated an investigation 
into the traction potential of the new engine. In due course emerged the parameters for the design of a revolutionary single-unit diesel-electric locomotive of a power substantially greater than existed at the time (or 
for some years after it’s subsequent introduction).

Alongside the production of well established designs for export the prototype began to take shape, finally going into proving service on the L.M.Region of B.R. in 1956, the most powerful single-unit d.e. loco in the world with the highest power/weight ratio. With 3,300 hp from its two 18-cyl Napier engines, the “Deltic” loco weighed some 108 tons, max. axle loading – 18 tons.

During extensive service trials, speeds of well over 120 mile/hour were reputed to have been reached (unofficially), due, principally to the extremely smooth riding of the loco under which speeds downgrade could build up without the rougher riding more normally associated with speeds around 100 mile/hour at that time.”

The notes went on to highlight the steady development of English Electric’s diesel engines and its rail traction success. The production “Deltic” locomotives went on to become legends on a par, if not exceeding that of the Gresley or Stanier pacific steam locomotives.

Teething troubles in the design were basically the result of its transfer to rail traction use, and for the prototype, in addition to the two engines it carried, no less than three were maintained as spares. This was partly for test purposes, and partly to seek out the cause and cure for major problems of erratic valve operation. On the locomotive, with two engines, should one fail completely, it was still possible to move using only the one remaining engine.

Ironically, the prototype Deltic was withdrawn from service and returned to the Vulcan Foundry in the same month the as the first production units appeared. A piston failure occurred while the locomotive was working a Kings Cross to Doncaster service, which badly damaged one of the engines, and during March, the power plant, train-heating boiler, traction motors and control system was removed. It was planned to scrap the remaining shell, before the proposal to display it in the Science Museum was made – and fortunately this proposal was successful.

The table below gives the leading dimensions and other principal details of the 22 Deltic locomotives, in ‘as built’ condition.

* Although when introduced, all the Deltics were fitted with both air and vacuum brake equipment, the latter being required since a majority of the passenger stock was still vacuum-fitted. The air brake equipment was for loco use only, and in 1967-8, the entire class was fitted with train air brake equipment.

Mechanical Details

(1) Power Equipment and Transmission

The two engines fitted into each locomotive were high-speed two-stroke diesels, each of which developed 1,650hp from eighteen cylinders. The design comprised three banks of six cylinders arranged around the sides of an inverted equilateral triangle, with all the piston heads opposite one another. This meant that instead of having the main crankshafts in the conventional position at the base of the engine, they were positioned at the three apexes of the triangle.

This complex construction, as previously mentioned was a development of a design produced by Napier for the Admiralty. In fact, the rail traction version, designated type D18-25 maintained the same size cylinders as some of the more powerful marine types, which in the 1950s had reached outputs exceeding 4000hp. One benefit gained from the triangular arrangement was the almost complete balancing of the reciprocating forces.

The pistons themselves were oil-cooled with an aluminium alloy skirt, and a dished alloy crown, screwed and shrunk onto the skirt. Three separate camshafts were fitted to the outer faces of the crankcases, with the fuel injection pumps mounted on the camshaft casings. Lubrication of the engine was based on a ‘dry sump system’, and all bearings and gears were supplied with oil under pressure.
The engines were constructed from three separate cylinder blocks and crankcases, secured by high tensile steel bolts – a method of construction reckoned to give a very strong and rigid structure. At the generator end of each engine a set of phasing gears was provided to drive a common output shaft. From the phasing gearcase, two flexible shafts passed through the uppermost crankcases to drive a centrifugal, double entry scavenge blower. The 5 1/8 in bore cylinders were fitted with steel ‘wet’ type liners with nine exhaust ports arranged around part of the circumference at one end of the liner, and 14 inlet ports around the full circumference at the opposite end.

The generators attached to the output shaft of the phasing gearcase were self-ventilated DC machines, with a continuous rating of 1,650 amps at 660 volts. The phasing gearcase output shaft to which the armatures were attached rotated at 1,125rpm – the speed being stepped down from the crankshaft speed of 1,500 rpm. The auxiliary generators were mounted above the main generators and driven by a take off shaft from the phasing gearcase at 1 2/3 the crankshaft speed. The 110-volt supply was used for excitation of the traction generator field coils, lighting and various ancillary circuits.

With both engines in operation, the load was shared between the auxiliary machines, and the main generators were connected in series to supply the six traction motors. Should one power unit fail, the system was designed to provide full tractive effort, but at only half normal road speed. The six English Electric Type EE 538 traction motors were nose suspended, axle hung machines, driving the respective axles through a pinion mounted on the end of the motor armature shaft, and a gear wheel on the axle. The motors were force ventilated, from blowers mounted in each nose end, and electrically connected as three parallel groups of two motors in series.

In order to improve the speed characteristics over which full locomotive power was available, two stages of traction motor field weakening were provided. Engine cooling was by means of two roof mounted radiator fans, each engine having a pair of fans driven through gearboxes and cardan shafts with universal joints.

(2) Control systems

Control of engine speed was by means of air pressure actuators acting on the spring loading of the engine governors. Excitation of each main generator was altered through the load regulators – multi contact rotary switches. The opening and closing of the contacts was via the engine governor and oil driven vane actuator. This in turn varied the resistance in the main generator field circuit, keeping the respective engine at full load for that specific position of the power handle.

All auxiliary circuits were supplied at 110volts, for the operation of pumps, blowers, compressors, etc. An electrical control cubicle was provided behind each cab bulkhead, and housed all the principal circuit protection devices. General protection devices included automatic correction of wheel slip, which involved a slight reduction in traction motor voltage and application of sand.

This arrangement for controlling wheel slip was also in experimental use in 1961 on the 2000hp English Electric Type 4 No D255.

In the event of high cooling water temperature, or low lubricating oil pressure, the engine affected was shut down automatically. Faults such as these would be indicated on the control desk in the driving cab, together with boiler shut down and general fault lights. The general fault light was linked to secondary fault indication lights in the engine compartment detailing particular faults, such as traction motor blower failure, low water or fuel level. The low fuel level indicator meant that enough fuel for only 50 miles of running remained.

(3) Bogies, Running Gear -General Constructional Features

The bogie main frames and bolsters were fabricated assemblies with the headstocks riveted to them. The general arrangement was similar to the prototype locomotive, though the wheelbase at13ft 6in, equally divided, was shorter. Underhung equalising beams of forged steel were fixed to stirrups incorporated in the axlebox assembly, with the stirrups and equalising brackets being provided with manganese steel liners. Similarly, liners were fitted to the wearing faces of the roller bearing axlebox guides, bolsters, side bearers and centre pivots. The load was transmitted to the bogie through the bolster side bearers and four nests of coil springs to two spring planks suspended by swing links from the bogie frame. Dampers were fitted between the bolster and spring planks. Four pairs of coil springs distributed the load from the solebar to the equalising beam.

This design of swing bolster bogie was also fitted to the English Electric Type 3Co-Co locomotives, and in June 1961,fractures were discovered in the transom webs of two locos, and as a result all locos with this type of bogie were withdrawn whilst a modification was made. This involved the provision of thicker gauge steel for the particular component, and no further trouble was experienced from this source on either the Type 3s or the Deltics. An interesting arrangement of ducting for traction motor cooling air was used, involving a flexible connection to two of the motors through the hollow bogie centre via the bolster, with similar ducting and flexible connections to the third motor. Clasp type brake rigging was fitted, and could be operated directly through the driver’s air brake valve, or operation of the vacuum brake on the train would cause a proportional application of the loco’s brakes to be made. In1967-68 all the Deltics were equipped with a train air brake system for working the latest stock, including air conditioning.

The underframe and body framing was designed as a load bearing structure, built up from cold formed steel sections and carried on two centrally positioned longitudinal members, and rolled steel channel solebars. A steel plate decking was welded to the top of the underframe with wells under the engine/generator units. All exterior and interior panelling was welded with joints ground flush. Fibreglass insulation was provided between the bodyside panels and in the cab, reducing noise and temperature variation. A more than usual proportion of fibreglass was used in the Deltics, with sections being adapted for battery and sand boxes, main cable ducts, instrument panels, cab and equipment compartment doors. The underslung fuel and boiler feed water tanks were welded up from light alloy sheet, and carried between the bogies. Water tanks were insulated and fitted with heating coils. A characteristic steam locomotive fitting was also provided on these advanced diesel locomotives – a water pick up scoop for use on troughs fitted between the rails.

Basically, the body could be divided into five compartments, which were as follows: No 1 end cab, engine room, boiler compartment, engine room, No 2 end cab. In front of each cab, a nose compartment housed various items of equipment. At the No 1 end these included two exhausters, CO₂ fire extinguishers and a traction motor blower and air filter. The nose end in front of the No 2 cab – in addition to the traction motor blower and fire fighting appliances – also housed a toilet and the air compressor. In each case, in view of the height of the nose, both Driver and Second man’s positions were on a raised platform within the cab proper, which was provided with an access door on either side. Due to the restriction of space caused by the intrusion of part of the control cubicle into the cab, the two outer doors were sliding, whilst the engine room access doors opened into the cab.

The engines were positioned in. the engine compartments so that the generators faced outwards, ie, towards the cab, and separated by the train-heating boiler. This latter occupied a space12ft I Din in length at the mid-point of the locomotive. It was a Spanner ‘Swirlyflow’ Mk II, with a steaming capacity of 15001b/hr.

Follow this link for Part 2 – Build & Operations

Further reading & Useful Links:

British_Rail_Class_55  (Wikipedia)

The Deltic Locomotives of British Rail – Brian Webb.  Pub. David & Charles 1982; ISBN 0-7153-8110-5

The Deltic Preservation Society

 

 

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