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ENGINEERING IS a process, not a result. An excellent example of this is development of the Rolls-Royce Merlin aircraft engine, renowned for powering the Avro Lancaster, de Havilland Mosquito, Hawker Hurricane, Supermarine Spitfire, and 39 others of the world’s aircraft.
The PV-12 stood for “Private Venture, 12-cylinder,” its PV indicating that Rolls-Royce received no government funding for development. Nor was it a straightforward success: As one example, the engine’s innovative evaporative cooling proved to be unreliable. Once U.S. ethylene glycol became available, the PV-12 was converted to conventional liquid cooling because of its efficiency.
The first Hawker Hurricanes and Supermarine Spitfires, entering production in 1936, were PV-12-powered. Government funding followed.
The Merlin I and its successors are given a detailed description in Classic World War II Aircraft Cutaways, by Bill Gunston, in association with The Aeroplane and Flight magazines, Osprey Aerospace, 1995. This book contains many period photographs as well as stunning cutaway drawings by J.H. Clark of The Aeroplane and Max Millar of Flight.
Gunston notes, “Many on the Allied side would say the Rolls-Royce Merlin was the greatest aero engine of World War 2. It was certainly the most famous. Incidentally, though in wartime RAF slang anything really good was called ‘wizard,’ and Merlin was a famous wizard, the engine was named after a bird of prey, like its predecessors.” The merlin is a small Northern Hemisphere falcon (Falco columbarius).
The Merlin was a V-12 with its vee aligned upward, unlike, for example, the Benz DB 601’s inverted-vee as installed in the Messerschmitt Bf 109. Gunston notes, “In the earliest drawings and mock-up, the engine was inverted, which has much to commend it (for example, in a single-engine aircraft it gives the pilot a better view when taxiing), but this arrangement was eventually considered un-British.”
This upright vee design had a set of reduction gears to translate the crankshaft’s rotation up to propeller height. Originally a double-helical gear, it was soon replaced with plain spur gears.
Engineering Refinements Continue. The Merlin had four valves per cylinder, two intake and two exhaust, actuated by a single overhead camshaft per bank. Though the engine featured one of the best superchargers in the world, its initial engineering displayed oddities of compressed air flow and other less- than-optimal ducting. An aerodynamicist, “Doc” Stanley Hooker, was charged with bringing things right with the supercharger and its intake ducting.
Also, notes Guston, “The carburettor float chambers incorporated the simple pierced diaphragms invented by Miss Tilly Shilling at Farnborough so that the engine kept running smoothly under negative-G (so that a [Messerschmitt] Bf 109 pilot couldn’t get away so easily by simply pushing the nose of his fighter over and diving for the deck—the favourite evasive maneuvre since the invasion of Poland.”
Just-in-Time Engineering. The result of these and other engineering refinements was the Merlin XX, which entered production in July 1940. The Battle of Britain commenced on July 10 of that year.
Guston notes, “Just in time for the Battle of Britain, 100-octane fuel became available, enabling boost pressure in combat power to be doubled, from 6 lb/sq in to 12 lb/sq in, raising power to over 1300 hp. This made a vital difference to the results of one-v-one combats against the Bf 109E.”
Hats off to “Doc” Stanley Hooker and Miss Tilly Shilling. And also to cutaway artist extraordinaire James H. Clark. ds
© Dennis Simanaitis, SimanaitisSays.com, 2018