Amberley Publishing - Transport, Military, Local and General History

The Merlin: The Engine That Won the Second World War by Gordon A. A. Wilson

The name sure conjures up a strong mysterious presence from a bygone age and that is what the Rolls-Royce Merlin is; not an ancient wizard from mediaeval times but a high-performance aircraft engine from another century. Over eighty years ago Frederick Henry Royce sat at his desk and further developed in concept some previous successful engines into the very successful Vee shaped twelve-cylinder liquid cooled aircraft engine.

C.S. Rolls. (c. Rolls-Royce Heritage Trust, The Merlin, Amberley Publishing)

The Royal Air Force fighters and bombers would never be the same after the introduction of the Rolls-Royce engine into their airframe. Names such as the Hawker Hurricane, Supermarine Spitfire and de Havilland Mosquito fighters and the Avro Lancaster bomber became synonymous with Britain’s victory in World War Two. The aircraft manufacturers provided the body, but it was Rolls-Royce that provided the heart to ensure that each aircraft, depending on its role, performed to the maximum at both very high or very low altitudes, and everything in between.

The finest example of this was when the Merlin engine replaced the Allison engine in the North American Mustang. It turned the technically superior airframe into arguably the best all round fighter/fighter escort of the war. The addition of jettisonable, ‘drop’, fuel tanks allowed the Mustang to escort the Boeing B-17 Flying Fortress all the way to Berlin and back and be a very effective fighter escort.

 

F.H. (Henry) Royce. (c. Rolls-Royce Heritage Trust, The Merlin, Amberley Publishing)

The name Rolls-Royce itself brings an understanding of precision, performance and unmistakeable beauty. Henry Royce started his innovative engineering by trying to build a better mousetrap, notably to improve his own twin cylinder Decauville. This he succeeded in doing and then followed up by developing his own car, a 10 Horsepower twin cylinder model. Joined by Charles Rolls in 1906 the partnership flourished. The backroom boffin and the aristocratic salesman adventurer, how could it fail? It did not, and the foundation was set for a company which today is known throughout the world.

The Rolls-Royce cars continued to improve for the next eight years and then the First World War intervened, production stopped except for some chassis conversions to armoured cars. Lawrence of Arabia comes immediately to mind driving his Rolls-Royce in the desert. The government immediately approached Rolls-Royce about building the Renault V8 and RAF 1a engines. As before, Royce, after examining these engines, immediately set out to design his own. He did, and it was called the Eagle. Royce had taken his experience with a V12 liquid cooled engine into the air. Twelve years from the road to the air. Aero engine development would accelerate rapidly for the next 100 years and Rolls-Royce was leading and competing with the ‘big boys’ of the aviation world.

The Eagle was followed by the Falcon, Hawk and Condor. All names conjuring up powerful birds freely soaring at will in the sky that they owned. Immediately after the war two Eagle engines proved themselves by powering a Vickers Vimy, under the command of John Alcock and Arthur Brown, non-stop across the Atlantic. The Kestrel and Buzzard engines maintained the company’s momentum until the entry of Rolls-Royce to win and capture for perpetuity the Schneider Trophy.

Rolls-Royce Eagle, the first aero engine. (c. Rolls-Royce Heritage Trust, The Merlin, Amberley Publishing)

The Buzzard was taken and developed to produce horsepower with little or no restraint for longevity, to last just long enough to complete the course at maximum horsepower. This was the ultimate learning foundation for the Merlin which would follow soon after. Streamlining, weight, special fuel and maximum supercharger performance was the total, only, demand of the R engine. Rolls-Royce succeeded by winning the 1931 contest, third time in a row. The Trophy now resides in the Science Museum, London.

The Goshawk appeared off the drawing boards using an evaporative or steam cooling system. The condensers changing the steam to liquid were bulky, inefficient and susceptible to damage. Its only claim to fame, before it was cancelled, was its installation in the Supermarine Type 224, which became the Spitfire. Something else was needed and that something was the Merlin.

1933 was in the middle of the transition of the biplane to the monoplane. Reduce the lift in half by removing a wing and it required the remaining wing to travel faster to achieve the same lift. Faster speed required more power and efficiency from the engine and the propeller. During this important transition and demand on engine design and performance the engineering heart of Rolls-Royce died in April 1933, Frederick Henry Royce passed away.

Supermarine Spitfire Mark IX. (c. Geoffrey Pickard, The Merlin, Amberley Publishing)

The momentum of his engineering foresight and guidance resulted in the personnel of Rolls-Royce to produce and run the Merlin for the first time in 1933. Twenty years from the Eagle to the Merlin. Changes to cylinder heads and block castings followed looking for the perfect balance of performance and ease of construction. This was an all risk situation for the company. If the Air Ministry was not interested in the Private Venture 12 engine, all the Rolls-Royce resources would have been for nothing and it would have been a very costly venture.

The Air Ministry loved the engine and to keep up with the demand had the engine built under licence in the USA. The biggest improvement for the engine came from the speeds and stages of the supercharger attributed to Stanley Hooker. The Merlin continued to develop from 740 to over 2,000hp in the Merlin 133/134.

In 2019 the eighty-six-year-old engine still can be heard in the skies of the world. Flying Avro Lancasters in Britain and Canada thrill the aviation enthusiasts with the sound of four Merlins at air shows. Ground running Lancasters in Lincolnshire, England and Alberta, Canada thrill the crowds. Add to this the sights, who can not admire the elliptical wing of the Supermarine Spitfire, of the Hawker Hurricane, the de Havilland Mosquito and the North American Mustang.

It is not the sight of the aircraft alone that thrills the audience but the unmistakeable sound of the twelve cylinders of the Merlin. Can you imagine the sound of the Merlins at the Reno air races in the USA? I look forward to the 100th anniversary, it is only 16 years away. I cannot wait!

Gordon A. A. Wilson's new book The Merlin: The Engine That Won the Second World War is available for purchase now.