Manic Motors

The astounding Napier Deltic Opposed-Piston Engine

This amazing device is perhaps nearing the top of the list for complex, intricacies in engine design. It is a prime example if what can happen when a designer stays up too late and fiddles with a concept until it is truly over the top. The only thing that surpasses the wildness of the concept is the fact that members of a board of governors in a major industrial corporation decided this deserved to go into production. Despite its complexity and “outside-the-box” thinking, the fantastic Deltic went on to power both boats and railway trains and was rather successful! 

A Bit of Background

The Deltic was an opposed-piston engine (note: not an opposed cylinder engine, although they generally can share a similar basic layout). This idea came about in the early days of reciprocating piston engine development and was thought to offer some advantages. Among these were the elimination of a cylinder head and the accompanying valve train with all its complexities. There was also the idea that two power strokes could be combined by linking the opposing pistons within a single cylinder.

With the idea of reducing complexity, this format lent itself best to the two-stroke diesel engine and one of the earliest proponents was the German Junkers Aircraft Company.

With a solid engineering background, the Junkers designers came up with a powerful design that could work well within the confines and lightweight requirements of aviation applications. The Junkers Jumo engine and its variants saw service in transport and military aircraft and performed reliably and was surprisingly efficient.

Taking Things Further

With the success of the opposed-piston, single cylinder concept, Junkers went on to add cylinders and pistons but continued to use the proven, vertical layout. At least until someone decided there could be an alternative and designers began thinking about even more crankshafts and cylinder-pairings. Of course, tying all these spinning and reciprocating components together into something that could produce a useful rotating output shaft required an assemblage of gears or chains or some other method that assured the motion and timing of everything would work out.

Junkers came up with a massive central gear that harnessed the power of the multiple crankshafts and brought everything together in a central output shaft. When coupled with an amazing rectangular layout of adjoining 90° Vee’s they birthed the incredible Junkers Jumo 234 engine. Believe it or not, it actually worked and found its way into aircraft!

Meanwhile, on the other side of the English Channel…

Back in Britain, there was a requirement for a powerful and compact diesel engine to power offshore patrol craft and smaller minesweeping vessels and some bright bulb decided the opposed-piston diesel was the perfect choice. The always creative Napier company had extensive experience in building unusual powerplants and despite their unorthodox designs, they were quite successful at making these things work. When someone at the firm came up with a set of 60° “Vees” with opposed-pistons and no less than 3 crankshafts, well the folks at the top were mightily impressed and figured the power produced by such a device would fill the marine powerplant bill perfectly. A single row, six-piston prototype was built to refine and prove the concept and it wasn’t long until multiple “rows” of cylinders and pistons were added to the mix. From two-row, 12-piston, six-cylinder versions all the way up to massive six-row, 36-piston, 18-cylinder engines were developed. There seemed to be no limit. Like the idea for increasing the power of radial aircraft engines, if you wanted more power and had the room, you just kept adding rows of cylinders!

The resulting triangular-formed engine was christened the Deltic due to its delta-shaped layout. In testing it showed promise and after some development, versions found their way onto British motor-torpedo and patrol boats. Advantages of the Deltic opposed-piston design included the previously mentioned deletion of the cylinder head along with all its associated valves and timing gear as well as the massive amount of power and torque that could be created from this relatively lightweight and compact engine. This proved to also be especially useful in the marine and rail applications. The drawbacks of the design were the excessive amount of smoke put out by these oil-burners and the complexity of the internal gearing required to keep the 3 crankshafts all spinning in proper time. Once sorted out however, the Deltics proved themselves to be the darlings of the Royal Navy’s fast patrol boat and minesweeping fleet. Deltic engines were used in these craft right up until the early 1980s and several ships including some of the Hunt Class minesweeping vessels are still running with Deltic powerplants.

In the early 1950s the British railways were also looking to update their steam-powered locomotives with more efficient and more powerful technology and the Napier Deltic engines aroused a lot of interest. The concept of high-speed rail transit in the U.K. meant a change in the basic technology was needed.

It was during the early post-war period when British Rail looked at the Napier Deltic and decided this powerful and compact engine could have a future powering some of the upcoming locomotives being developed to replace the coal and oil-fired steam engines of the day. With blessings from the higher powers, Napier went on to design and develop the Deltic rail engines. These came into widespread usage in the U.K. on the newest generation of high-speed trains introduced in the mid-1950s and served through their final showings in regular service in the early 1980s. It should also be pointed out that although the Deltic locomotives were removed from regular service in the early 80s, several were rescued from the scrap heap, restored for museums and pressed into service as luxury rail-tour locomotives. There were even a couple of Deltics that resumed regular service, albeit on privately-owned railway lines. To this day, there is a dedicated following of enthusiasts for these fascinating locomotives, and it is said there is nothing that sounds quite like a Deltic engine, especially when running at full chat! For those who would like to experience the glorious noise there are videos online. You can watch one below.

Check out the full article and photos in the Moto/ology Flip/book!