THE ROLLS-ROYCE MERLIN
EVERY BOY WHO EVER READ A WAR COMIC OR WAR STORY HAS READ OF THIS MOTOR
THE MOTOR THAT FOUGHT FOR FREEDOM
A motor that was built to protect our freedom. Seventy-five years ago and more it had won dominance of the skies and was powering aircraft that were protecting the troops on the Normandy beaches.
Ithis t’s manufactured from aluminium alloy; has overhead cams; has 12 cylinders in a 60-degree V-formation, each with four valves; produces prodigious horsepower; and has an unmistakable sound, yet it’s not in an Italian supercar.
is the 27-litre Rolls-royce-designed engine, and, rightly or wrongly, it is often termed ‘the motor that won the war’.
Development
Rolls-royce had already made its mark in the aero-engine world with a V12 that had powered various aircraft to various records, but, by 1933, it wanted to build something more powerful for what it perceived as a market that was bound to grow in the near future. Germany was rearming, and there was a need to at least keep up with it in the arms race.
The directors of Rolls-royce christened this development ‘Project PV-12’, with ‘PV’ referring to ‘private venture’ (no government money) and the ‘12’ to the number of cylinders. A V-formation of the cylinder layout — therefore, liquid cooled — was chosen, as this gave major advantages aerodynamically. Speed was what Rolls-royce was after, for a fighter aircraft.
Early versions of the engine produced massive power, but it took more than a few prototypes to iron out problems such as oil and coolant leaks, and cylinder-head, gear, and other component failures. Eventually, though, there was a version that was very reliably producing over 1000hp (746kw).
This coincided with the British Government’s Air Ministry call for a fighter aircraft capable of at least 310mph (499kph).
Early test models of both the Hurricane and the Spitfire flew with versions of the now ‘Merlin’-monikered engine. Aircraft were ordered from these companies, and Rolls-royce was finally awarded government money to further bankroll the project. Rolls-royce had a tradition of naming its engines after birds, and ‘Merlin’ was an ideal name for this new engine, as the merlin is described as a swift flyer and able hunter, something for which the engine would become famous.
Production
Design work for the engine began in the early ’30s, and the first engine was tested in 1933. With the shadow of war spreading, the British Government began ordering the engines, so the Rolls-royce factory at Derby was converted to Merlin production. A second factory was immediately built at Crewe, and then another massive factory was constructed in Glasgow. The first production examples of the engine were being built in 1936, and, by 1939 — only one month after the outbreak of World War II — all three Rolls-royce factories were dedicated to turning out the Merlin.
Rolls-royce continued development of the motor and used its own labs to develop alloys for the engine’s construction. ‘Rolls-royce 50’ was a special aluminium alloy developed by the company. It was used in the engine blocks, casings, and heads. Various alloys for bearings were also created using bronze, lead, bronzesilver, and bronze-iridium mixes.
The scale of this motor project was audacious, to say the least. At the factory sites, thousands of homes were constructed to house the workers. In Crewe, 1000 new houses were built for some of the 16,000 workers, while the new Glasgow factory created a need for 1500 new homes. There were 14,000 employees at the Ford plant in Trafford Park, Manchester.
Ford UK had joined the team in making these motors in Britain, but, in the US, Henry Ford had his reasons for refusing to join the war effort at that stage. Rolls-royce shipped motors to the Packard company in the US, and it began a very successful project in manufacturing these motors under license to Rolls-royce. The Packard motors were essentially the same as the British ones, although they were manufactured in the US and not just assembled there.
The Battle of Britain was fought and won with exclusively Uk-made motors; the Packard versions were fitted to aircraft after that. Of course, post-war legends have built up as to which factory produced the best motors, but in light of today’s research, it seems that all these motors performed admirably.
The war effort took its toll on the availability of the male workforce, so women stepped in and staffed the benches. Wartime Britain was still unionized and even then showing its prowess at industrial action. For a brief period after the outbreak of war, the Rolls-royce workers ‘withheld their labour’ because women had taken ‘skilled’ positions in the workforce. Eventually, women accounted for about 50 per cent of Rolls-royce’s workforce during the war.
The legend
Although the Merlin motor is synonymous with the Hurricane, the Spitfire, the Lancaster, and the Mosquito, it was actually fitted to more than 40 types of aircraft. It was the Lancaster, using four per aircraft, that was the most common user of this power unit. The Mosquito twin-engined bomber followed that, then the Spitfire and the Hurricane. The American P-51 Mustang was originally fitted
The motor was a technical marvel: more than 11,000 individual parts, created from tens of thousands of hand-drawn blueprints, all out of the Rolls-royce design office
with an Allison motor, and it was only after it was repowered with the Merlin that it gained its reputation as one of the best fighter aircraft of the war.
The motor was a technical marvel: more than 11,000 individual parts, created from tens of thousands of hand-drawn blueprints, all out of the Rolls-royce design office. During its lifetime, it more than doubled its horsepower rating. The early versions produced just over 1000hp (746kw); by the end of the war, an increase in the fuel octane rating from 87 to 100, plus various developmental changes to the motor, meant that it was reliably producing 1600hp (1193kw). The development of a two-stage supercharger enabled a significant power increase to just over 2000hp (1491kw). Spitfires equipped with this motor were more than 62mph (100kph) faster than the earlier models. Rolls-royce eventually extracted 2640hp (1969kw) from test versions. Time between overhauls stretched to 650–800 hours from an original 50, although wartime aircraft often had a life of even less than that. During some of the worst times of the war, the average service life of a Lancaster was approximately 40 hours.
That supercharger was a part of the motor that was continually developed during the production life of the Merlin. The version that carried most aircraft through the war was a single-stage two-speed system. The aircraft would use the lower gear to spin the rotor at take-off and lower altitude, but would engage the higher gear at over 10,000 feet (3048m). The rotor speed was then about 25,000rpm, and the peripheral edge of the rotor was spinning faster than the speed of sound.
Flying like this, each motor was gulping 30 gallons of fuel an hour (136 litres per hour) and a bus full of air every minute. The flattened, or ‘fishtail’, exhaust ports were then exiting the gases at over 1243mph (2000kph). Early on, Rolls-royce found that these produced a significant jet thrust that, if directed rearwards, added 10mph (16kph) to the aircraft’s top speed.
The development of a two-stage supercharger enabled a significant power increase to just over 2000hp (1491kw). Spitfires equipped with this motor were more than 62mph (100kph) faster than the earlier models
The legacy
By war’s end, 150,000 Merlin motors had been produced, with more than 50 variants being developed, and the motor had entered the halls of fame for its dependability. Lancaster crews were often able to return to their base with one engine shot out and the remaining three on full power for up to four hours without further mechanical issues. Rolls-royce continued production of the motor until 1956.
The engine was used in both military and civilian aircraft; one of the final installations was with the Spanish Air Force’s Messerschmitt 109s. At the time, these aircraft were being built in Spain, but the supply of Daimler-benz engines had dried up, so the Merlin was used instead. It is ironic that the first and last versions of the greatest enemy of the Hurricane and the Spitfire, the ME 109, were both Rolls-royce powered — prototype ME 109s were developed with the Rolls-royce Kestrel motor.
There was also a marine version and a nonsuper-charged version. In the later of these two versions, some of the aluminium was replaced with cast iron. They became the Rolls-royce ‘Meteor’, which was used as a tank engine.
Post–world War II, Rolls-royce shifted its attention to jet engines, but today there are still plenty of these old Merlins flying. In the UK, the Battle of Britain Memorial Flight flies aircraft powered by these motors. They are regularly seen above London and other British cities. Here in New Zealand, there are also a number of Merlin-powered aircraft still operating. Auckland company Avspecs has rebuilt a Mosquito bomber and Spitfires, and happily provided us with access to a motor and aircraft for this article.
Familiarize yourself with the sound of the motor: a deep, harsh roar that offered comfort, or fear, to both those above and those below during the war; you will still get the chance to see and hear these marvels for many years yet.