At the end of the last piece on the development of Aero engines we had just reached the water cooled V12 designs pioneered by Curtiss and later refined by Rolls Royce in the Kestrel and “R”. The Second World War would be dominated by these designs on both sides of the conflict – alongside a number of pre war radial designs. As with previous instalments this post takes a brief look at a selection of iconic engines from the conflict and how engine development progressed with a number of manufacturers.
Where else can you start with a Second World War engine post than Rolls-Royce. This legendary name had already been responsible for the pre war Kestrel which powered the great Hawker Biplane fighters of the 1930s as well as the “R” series that would power R.J Mitchell’s Supermarine S.6 to Schneider Trophy glory.
Merlin – 1935
Arguably the most iconic name in aero engines and an unmistakable sound. The Merlin first flew in February 1935 powering a Hawker Hart. This initial version of the engine, known as the PV-12 produced 740hp, only two of these original prototype engines were ever built. That first design was followed by a series of test Merlins each given their own identifying letter – The B, C and E were all development versions, with the latter powering the Prototype Spitfire, by now producing over 1,000hp.
The next model produced, the F, would later become known as the I and would become the first model to be used in a production aircraft, namely the Fairey Battle.
The story of the Merlin is unquestionably intertwined with that of the Spitfire so it makes sense to follow the development of this power plant alongside the Spitfire. Early Spitfires were powered by the Mk II Merlin, with the design progressing to the 1,150hp Mk XII by the time the Spitfire II came around. The last of the short Merlins, an as a result the “baby” Spitfires came with the Mk V which was powered by the Merlin 45, the engine was now producing 1,515hp.
By 1942 aircraft and aero-engine development was developing quickly, the Spitfire needed more power at higher altitudes to compete with the latest variants of the BF109 and FW190 fighters. This led to a two stage supercharger being added to the back of the engine. This addition created the Merlin 61 now capable of putting out 1,565hp across a range of altitudes.
The Merlin development ultimately led to the Merlin 266 which powered the Mk XVI Spitfire, providing 1,710hp, an impressively versatile design progressing from the original 740hp.
Rolls-Royce weren’t the only company to produce the Merlin engine during the war of course, Packard manufactured the engine under licence in the United States. This variant of the type powered the P-51 Mustang, creating another icon of the Second World War.
I’ve focused primarily on the Spitfire here as the Merlin and that design go hand in hand. I should also mention the other types that made use of this engine during the war including the Lancaster, Hurricane, Mosquito and many others.
Alongside the Rolls-Royce and Packard built V12s, the other main allied in-line power plant was the Alison V-1710. This engine was first run in 1930 and was designed to meet the new requirement for a liquid cooled engine capable of producing 1,000hp in order to power ever improving bomber and fighter designs. Despite being run as early as 1930 with a view to being used for the US Navy airships, the engine would not actually take to the skies until 1936.
The basic V-1710 was a 12 cylinder 28 litre unit. The production techniques utilised for this engine were revolutionary. The basic power unit was constructed separately allowing for the various gearbox, turbo/supercharger and propellor accessories to be added afterwards. This meant that one production line could churn out engines capable of being used on any of the aircraft that required them. The result was that even complex arrangements such as the counter rotating engine on the Lockheed P-38, designed to remove the effects of torque, could be applied to one engine, while the standard layout for a P-40 could be applied to the next. This resulted in incredible versatility.
While this versatility was much needed and appreciated, the engine was let down by its lack of high altitude supercharger. Other units such as the Merlin made use of this and the result was much higher performance at altitude. This of course led to the Alison being replaced for the P-51 Mustang. This also relegated the P-40 family to being largely used at lower levels of combat.
just like the other engines in this series, there was a considerable uplift in power by the time the final variants rolled off the production line. The final Alison V-1710s were rated up to 2,300hp.
The V-1710 saw use in aircraft such as the P-40, P-51a, P-38 and P-39 amongst others. In recent years the engine has proven to be a popular replacement for more elusive V12 arrangements. Alisons have replaced the original Russian power plants of the recent run of Yak-3/9 reproductions alongside the Mig-3 and Il-2 Sturmovik restorations.
Griffon – 1939
Two iconic engines come to mind when you think of Rolls-Royce in WW2, the Merlin and the Griffon. Many naturally assume that the Griffon was a development of the Merlin, it’s roots can actually be traced much further back. The need for the Griffon came from a requirement for the Royal Navy and Rolls-Royce returned to the Schneider “R” engine which had powered RJ Mitchell’s racing seaplanes to victory in the late 20s.
The basic Griffon design consisted of a 60 degree V arrangement with a capacity of 37 litres, early versions, fitted with a single stage supercharger could provide 1,735hp while later models with a two stage supercharger resulted in power in excess of 2,000hp (2,375hp in the 60 series engines).
As well as extensive use in the later incarnations of the Spitfire the Griffon also powered the Shackleton, Firefly and has powered a number of Reno unlimited racers over the years.
Daimler Benz is certainly the iconic aero engine name for the Luftwaffe in WW2, it powered many of the German aircraft from the conflict, notably the BF109 under many different models. The DB600 series started with a model of the same name in the 1930s.
DB601 – 1935
The 601 provided a fair match to the Merlin early in the war; a liquid cooled inverted V12 design, the first production example provided over 1,000hp. This initial variant had a slight power advantage over the British engines of the time but the big advantage was that the engine benefited from Fuel Injection, the first engine to have this, allowing the engine to keep running under negative G, something that the Merlin did not have.
The 601 had a capacity of 33 litres and features the distant exhaust layout thanks to the inverted design with comparison to other V12 engines of the era. This gives the 109 its distinctive cowling arrangement with the exhaust stacks at the bottom of the cowling.
The DB601 led to a new world speed record, when the Messerschmitt 209, a racing aircraft in the hands of Fritz Wendel reached a speed of 469mph in April 1939. This record was not broken by a single engined piston aircraft until 1969. An example of the fuselage of this impressive aircraft can be found at the Polish Aviation Museum in Krakow.
DB605 – 1940s
The ‘605 was the next logical step from the ‘601. This new engine saw larger displacement, with the cylinders being bored out further to provide greater performance. This engine also saw the introduction of a new, more powerful Supercharger. This took the power from 1,300hp to nearer 1,500hp.
The ‘605 was not without problems, with engine fires being fairly common. Despite these issues it proved to be a popular and widely used engine just like its predecessor. Its most famous uses would have been the ME110 and ME109G. Examples of this engine can be seen in the air today powering EADS Buchon conversion “Red 7” amongst other 109/Buchon hybrids under restoration.
Much like the Merlin and a Spitfire the distinctive growl of the Daimler Benz goes hand in hand with the sight of a Messerschmitt 109, especially as that gentle supercharger whine kicks in.
801 – 1939
During the 1930s BMW had acquired to licence to produce Pratt & Whitney Radial Engines in Germany. This line of engines powered a number of notable types including the Junker JU52. The 801 is perhaps best known as powering the Focké-Wulf 190, one of the most renowned German aircraft from the Second World War.
The early variant of the 801 came about following early testing of the Fw190 which had been using the BMW 139. Engine cooling was becoming a real problem and BMWs solution was simply to design an entire new engine. While this new design featured a number of outdated features, such as a single stage supercharger, it was also ahead of its time. The new 801 benefited from what was known as a Kommandogerät, this basically meant that with any movement of the throttle, all the key settings (such as mixture and propellor pitch), were adjusted accordingly. This was revolutionary and would have given pilots much more time to focus on the challenges of combat, rather than keeping the engine running.
This initial design was a seven cylinder radial which provided 1,500hp initially, eventually extending to 2,400hp by the end of the war, proving the 801 to be another engine that undoubtedly played a key part in the development of the war.
Much like the famous Daimler Benz powerplants, the 211 was an inverted V12. The engine saw great success in a number of German bomber aircraft. The 211 was first unveiled in 1935 and featured direct injection, providing 990hp. This first example was soon followed by the 211a in 1937 which saw performance improved to 1000hp with a number of different supercharger options available depending on high or low altitude use.
Once the war had begun, in 1940, the 211 needed a real improvement in order to compete with the Daimler Benz units used by the Messerschmitt fighters. These changes resulted in the 211F, able to run at much higher speeds and provide 1,400hp. It is no surprise given that junkers built a number of the notable German bomber aircraft, that the 211 saw extensive use in early war bombers. Ultimately the Jumo probably benefited from the fact that demand was so high and the DB options were far more suitable for single engined, high speed use.
The 211 will often be overshadowed by the DB series of engines when anyone mentions inverted V12s, but any engine that powered such notable machines such as the HE111 and Stuka cannot be ignored.
Perhaps the most famous of the Japanese aero engines is the Nakajima Sakae, well known as the power plant for the famous “Zero” fighter that cause US forces in the Pacific so many problems. The Sakae first ran in 1939 and was a 14 cylinder, twin row radial that could produce up to 1,130hp. While the power may have been down compared to other engines in the conflict the Zero was an irreducibly lightweight fighter and this meant the Sakae provided plenty of performance.
This engine actually came from a much earlier design, the Ha5, which has roots stretching back to the First World War, when Nakajima first started producing aeroplanes. By 1920 they had their own aero engine factory though this only began with very basic two cylinder units. With the worldwide progression from rotary to radial Nakajima acquired the license to produce the Bristol Jupiter and later studied the Pratt & Whitney Wasp. These studies would lead to the production of the the first all Japanese produced engine in 1930, the Kotobuki. Following the success of this 9 cylinder engine work began on a higher power 14 cylinder unit which would be designated the Ha5, first running in 1933. One notable use for this engine was powering the Mitsubishi KI-21 as pictured below.
The original variants of the Ha5 produced only 650hp but by the end of its production line it was nearing 3,000hp – an impressive design range for any product. This engine would provide power for a great number of Japanese fighters during the war.
As with aircraft designs, the final piston engine developments before the jet age really pushed the boundaries of performance. One engine that any British warbird enthusiast will be familiar with, especially when paired with a Hawker Sea Fury, is the Bristol Centaurus.
The Centaurus is a two-row, 18 cylinder radial engine, capable of providing 3,000hp from a sleeve valve design. For a design perceived as one of the final developments of piston engines, it’s origins actually date back to the late 1910s and the first prototype ran in 1938. Following those early runs, production started in 1942. It would take some time for aircraft design to catch up with the power that the new Bristol unit would provide. Ultimately the Centaurus would not see active service until the war was almost over, with notable use in the Hawker Tempest II.
The Bristol design did go on to see a great deal of use following the war though. The Sea Fury is a notable airframe to benefit from this impressive unit as a well as a number of post war airliners and transport types such as the Airspeed Ambassador and Blackburn Beverley.
In recent years UK airshow enthusiasts have been treated to the unique sound of the Centaurus in the air, propelling a number of Hawker Sea Fury and Fury designs through the skies. Though the engine appears to have had a troubled past in civilian hands there is no denying the incredible power the machine provides, not to mention that wonderful sound.
Perhaps one of the most ambitious piston engines produced during the Second World War was the Napier Sabre. This engine featured 24 cylinders in an “H” arrangement. Napier had made a name for themselves during the 1920s and 30s with a number of their products powering flying boats alongside a number of British entries in the schnieder trophy races. Much like the Bristol radial engines of the period, the Sabre made use of Sleeve Valves – something which was pioneered by Harry Ricardo in the late 1920s.
The first prototype of this ambitious engine ran in 1938 and initially produced 1,300hp. By the end of 1940 this same design was delivering in excess of 2,000hp, an extraordinary figure for the time.
Once the engine was lined up for production, the story changed in tone. Following the carefully assembled prototypes it was found that the Sabre represented a significant challenge for mass production. Early production examples were plagued by problems with sleeves failing leading to seized cylinders. A number of other smaller issues were also commonplace, though it is unclear how much of this was the lack of instruction amongst mechanics on the finer points of this highly tuned machine. The Sabre V (2,400hp) powered iconic fighters later in the war such as the Hawker Typhoon and Tempest V. Impressively the Sabre was subject to further development following the war which resulted in one engine being tested at 5,500hp.
The Sabre’s unique design resulted in increased performance for the capacity of engine and even after American radial designs caught up in terms of horsepower, they were far larger units. Hopefully as part of the Hawker Typhoon Restoration Project, it may not be too long before we hear a Sabre growling again!
By the time engines such as the Griffon, Sabre and Centaurus had reached their full potential, the path had already been set for the last days of the highly tuned piston engine. The Military aviation world would soon be taken over the inevitable start of the jet age. These early jets will form the basis of the final part of this series.
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