Rolls-Royce Eagle

Eagle
Rolls-Royce Eagle VIII at the Canada Aviation Museum
Type	Piston V-12 aero-engine
Manufacturer	Rolls-Royce Limited
First run	February 1915
Major applications	Airco D.H.4 Vickers Vimy
Number built	4,681
Developed into	Rolls-Royce Falcon

The Rolls-Royce Eagle was the first aero engine to be developed by Rolls-Royce Limited. Introduced in 1915 to meet British military requirements during World War I, it was used to power the Handley Page Type O bombers and a number of other military aircraft.

The Eagle was the first engine to make a non-stop trans-Atlantic crossing by aeroplane when two Eagles powered the converted Vickers Vimy bomber on the Transatlantic flight of Alcock and Brown in June 1919.

At the outbreak of World War I in August 1914, the Royal Aircraft Factory asked Rolls-Royce to develop a new 200 hp air-cooled engine. Despite initial reluctance they agreed on condition that it be cooled by water rather than air, as this was the company's area of expertise.

Development of the new 20 litre engine was led by Henry Royce from his home in Kent. Based initially on the 7.4 litre 40/50 Rolls-Royce Silver Ghost engine, and drawing also on the design of a 7.2 litre Daimler DF80 aero engine used in a 1913 Grand Prix Mercedes that had been acquired, the power was increased by doubling the number of cylinders to twelve and increasing their stroke to 6.5 inches, although their bore remained at 4.5 inches of the 40/50. The engine was also run faster, and an epicyclic reduction gear was designed to keep the propeller speed below 1,100 rpm. To reduce inertia and improve performance the valvetrain design was changed from sidevalves to a SOHC design, closely following the original "side-slot" rocker arm design philosophy used on the contemporary German Mercedes D.I, Mercedes D.II and Mercedes D.III straight-six aviation powerplants.

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