Napier Deltic powered British Rail Class 55 Alycidon, at the National Railway Museum, York, UK

The term Deltic (meaning in the form of the Greek letter Delta) is used to refer to both the opposed piston high speed diesel engine designed and produced by Napier & Son, and the locomotives produced by English Electric using these engines, including their demonstrator locomotive named DELTIC and the production version for British Railways, who designated these as Class 55. Image File history File links Download high resolution version (2839x1833, 3147 KB) Napier Deltic, Alycidon, at the National Railway Museum, York. ... Image File history File links Download high resolution version (2839x1833, 3147 KB) Napier Deltic, Alycidon, at the National Railway Museum, York. ... British Rail assigned Class 55 to the twenty-two English Electric Type 5 express diesel locomotives built in 1961/2 and used for high-speed service on Britains East Coast Main Line between London Kings Cross and Edinburgh. ... Locomotives arranged around the turntable in the Great Hall. ... York is a city in northern England, at the confluence of the Rivers Ouse and Foss. ... For other uses, see Delta. ... Napier & Son were one of the most important English aircraft engine manufacturers in the early to mid 20th Century. ... English Electric was a 20th century British industrial manufacturer with a base in electric motors that expanded to include railway locomotives and aviation before eventual inclusion as part of GEC. // History The English Electric Company was formed in 1918 and, during that year and 1919, acquired control of Dick, Kerr... DP1, or DELTIC as it is more popularly known, was a demonstrator locomotive built by the English Electric company in 1955. ... British Railways (BR), later rebranded as British Rail, ran the British railway system, from the nationalisation of the Big Four British railway companies in 1948 until its privatisation in stages between 1994 and 1997. ... British Rail assigned Class 55 to the twenty-two English Electric Type 5 express diesel locomotives built in 1961/2 and used for high-speed service on Britains East Coast Main Line between London Kings Cross and Edinburgh. ...

History

An animated schematic of a Deltic engine. The inlet is coloured green and the outlet purple. Notice the bottom shaft contra-rotating with regard to the other 2 shafts, the lag between the exhaust and inlet ports opening and that ignition occurs when the pistons are not at equal positions in the cylinder.

The Deltic story began in 1944 when the British Admiralty commissioned Napier to design a diesel engine for their Motor Torpedo Boats and other lightweight, high speed craft. Hitherto in the Royal Navy, such boats had been driven by gasoline engines but this fuel is obviously highly flammable and made them very vulnerable to hostile fire, putting them at a disadvantage compared to their German opponents, the diesel-powered E-boats. Image File history File links Napier_deltic_animation. ... Image File history File links Napier_deltic_animation. ... The steert engine is a type of internal combustion engine; more specifically, it is a compression ignition engine, in which the fuel is ignited by being suddenly exposed to the high temperature and pressure of a compressed gas, rather than by a separate source of ignition, such as a spark... Motor Torpedo Boats (MTB) was the name given to fast torpedo boats by the US and Royal Navies. ... The Royal Navy of the United Kingdom is the senior service of the British armed services, being the oldest of its three branches. ... E-boat is the British and American name for the German Schnellboot (S-boot), a small, fast torpedo boat a little larger than the American PT boat and the British MTB. Specification Length - 34. ...

Up to this point, diesel engines were characterised by their poor power-to-weight ratio and their slow speed. However Napier had been working on various aviation diesel designs, licensed versions of the Junkers Jumo 204, prior to the start of the war. The Admiralty felt these would be a reasonable starting point for the larger design they required. Power-to-weight ratio is a measure commonly used when comparing various vehicles (or engines), including automobiles, motorcycles and aircraft. ... The Junkers Jumo 205 aircraft engine was the most famous of a series of diesel engines that were the first, and for more than half a century, the only successful diesel aircraft engines. ...

The original Napier Culverin was an opposed piston design, meaning that instead of each cylinder having a single piston and being closed at one end with a cylinder head, the elongated cylinder would contain two opposing pistons driving in opposite directions toward the middle. This led to a fairly "flat" engine that was originally intended to be buried in the wings of large aircraft. The Admiralty required a much more powerful engine, however, so for the added power Napier took three of their original Culverins and "bolted them together". This article is about existing engine designs. ...

The result was an inverted triangle, the cylinder banks forming the sides of the triangles, tipped by three crankshafts, one at each corner of the triangle. The crankshafts were connected together with phasing gears to drive one output shaft. Various models of Deltic engine could be produced with varying numbers of such three-cylinder banks, though nine and eighteen cylinders were the most common models, being of three and six cylinders per bank respectively. Crankshaft, pistons, and flywheel Continental engine marine crankshafts, 1942 For the comic strip about an old, curmudgeonly bus driver, see Crankshaft (comic strip). ...

Perhaps one of the more interesting features of this engine was the clever way the crankshaft phasing was arranged to allow for exhaust port lead and inlet port lag in the gas-flow of the engine. These engines are called 'uniflow' designs because the flow of gas into and out of the cylinder is one-way, and is assisted by some mild supercharging to improve cylinder scavenge.

Napier Deltic engine at the National Railway Museum, York, UK

Also of interest, was that prior attempts at designing such an engine had failed, as it appeared to be impossible to arrange the pistons to move in the correct manner, for all three cylinders in one delta. Napier realised that this problem could be solved by gearing the crankshafts such that one of them rotated in the opposite direction to the other two. Image File history File links Download high resolution version (2661x1824, 2703 KB)Napier Deltic Engine at the National Railway Museum, York. ... Image File history File links Download high resolution version (2661x1824, 2703 KB)Napier Deltic Engine at the National Railway Museum, York. ... Locomotives arranged around the turntable in the Great Hall. ... York is a city in northern England, at the confluence of the Rivers Ouse and Foss. ...

In an opposed piston design with no inlet or exhaust valves, and no ability to vary the port positions, the deltic design arranged each crankshaft to connect two adjacent pistons operating in different cylinders in the same plane, using forked connecting rods, one an 'inlet' piston used to open and close the inlet port, and an 'exhaust' piston in the adjacent cylinder to open and close the exhaust port.

However, crankshaft connecting-rod journals were so arranged that the exhaust piston 'led' the inlet piston by 20 degrees of crankshaft rotation. This meant that in any one cylinder, the exhaust piston reached its top-dead-centre position before the inlet piston in the same cylinder, and that the exhaust piston was on its way down the cylinder before its inlet piston mate reached its top-dead-centre position.

This clever arrangement allowed the exhaust port to be opened well before the inlet port, and allowed the inlet port to be closed after the exhaust port, which led both to good scavenging of the cylinder of combustion gas residues, and good volumetric efficiency for the fresh air charge. However, the arrangement suffered from the disadvantage that the two pistons did not contribute equally to the power output.

The first Deltic unit was produced in 1950, and by January 1952 six engines were available, enough for full development and endurance trials. An ex-German E-Boat, powered by three Mercedes-Benz diesel engines, was selected for these trials, since its power units were of approximately equal power to the new 18-cylinder Deltic engines. Two of the three Mercedes-Benz engines were replaced with Napier Deltics, the compactness of the Deltic graphically shown here - they were half the size of the original engines. E-boat is the British and American name for the German Schnellboot (S-boot), a small, fast torpedo boat a little larger than the American PT boat and the British MTB. Specification Length - 34. ...

Proving successful, the Deltic diesel engine became a commonly used powerplant in small, fast naval craft. The Royal Navy used them first in the Dark Class Fast Attack Craft, and subsequently in a number of other smaller attack and minesweeper classes. Napier Deltic engines are still in service in Hunt Class Mine Countermeasure Vessels. The Royal Navy of the United Kingdom is the senior service of the British armed services, being the oldest of its three branches. ... For the World War I minesweepers, see Hunt class minesweeper. ...

In addition, Deltic diesels served in MTBs and PT Boats built for other navies; particularly notable being the Norwegian built Tjeld (Nasty) class, which were also sold to Germany, Greece, and even the United States Navy. PTF Nasty class boats served in the Vietnam War in largely a covert ops role. PT boats in line A PT boat was a motor torpedo boat (hull classification symbol PT, for Patrol Torpedo), a small, fast vessel used by the United States Navy in World War II to attack larger surface ships. ... The United States Navy (USN) is the branch of the United States armed forces responsible for conducting naval operations around the globe. ...

While the Deltic engine was certainly successful and amazingly powerful for its size and weight, it was also a highly-strung beast, requiring a lot of care and maintenance. This was made much simpler by a policy of maintaining by unit replacement rather than repair in place - rather ahead of its time. Deltic engines were also easily removed should they break down, generally being sent back to the manufacturer for repair.

External links

• Deltic technical details.
• The Deltic Preservation Society.
• Hunt Class deltic powered Mine Countermeasure Vessel.