page_title: Rolls-Royce R
section_title: Description
hierarchical_section_title: Rolls-Royce R / Design and development / Description
caption_attribution_description: English: Sectioned view of the Rolls-Royce Merlin aero engine cylinders and valve gear. Taken at Royal Air Force Museum Cosford.
context_page_description: The Rolls-Royce R was a British aero engine designed and built specifically for air racing purposes by Rolls-Royce Limited. Nineteen R engines were assembled in a limited production run between 1929 and 1931. Developed from the Rolls-Royce Buzzard, it was a 37-litre capacity, supercharged V-12 capable of producing just under 2,800 horsepower, and weighed 1,640 pounds. Intensive factory testing revealed mechanical failures which were remedied by redesigning the components, greatly improving reliability.
  The R was used with great success in the Schneider Trophy seaplane competitions held in England in 1929 and 1931. Shortly after the 1931 competition, an R engine using a special fuel blend powered the winning Supermarine S.6B aircraft to a new airspeed record of over 400 miles per hour. Continuing through the 1930s, both new and used R engines were used to achieve various land and water speed records by such racing personalities as Sir Henry Segrave, Sir Malcolm Campbell and his son Donald, the last record being set in 1939. A final R-powered water speed record attempt by Donald Campbell in 1951 was unsuccessful.
context_section_description: The R was a physically imposing engine designed by a team led by Ernest Hives and including Cyril Lovesey, Arthur Rowledge and Henry Royce. The R shared the Buzzard's bore, stroke and capacity, and used the same 60-degree V-12 layout. A new single-stage, double-sided supercharger impeller was designed along with revised cylinders and strengthened connecting rods. The wet-liner cylinder blocks, crankcase and propeller reduction gear castings were produced from "R.R 50" aluminium alloy; and because of the short life expectancy of these engines, forged aluminium was used to replace bronze and steel in many parts. 
  To make the R as compact as possible, several design modifications were made in comparison to the Buzzard: the propeller reduction gear housing was reshaped, and the camshaft and rocker covers were modified to fair into the shape of the aircraft's nose, the air intake was positioned in the vee of the engine (which also helped to avoid the ingress of spray), and beneath the engine the auxiliaries were raised a little to reduce the depth of the fuselage. The engine's length was minimised by not staggering its cylinder banks fore and aft, which meant that the connecting rods from opposing cylinders had to share a short crankshaft bearing journal known as the "big end". This was initially achieved by fitting one connecting rod inside the other at the lower end in a blade and fork arrangement; however, after cracking of the connecting rods was found during testing in 1931, the rod design was changed to an articulated type.
  The introduction of articulated connecting rods was regarded as a "nuisance" by Arthur Rubbra, a Rolls-Royce engine designer, as there were inherent problems with the arrangement. The complicated geometry meant that a pair of rods had different effective lengths, giving a longer stroke on the articulated side; consequently the cylinder liners on that side had to be lengthened to prevent the lower piston ring from running out of the cylinder skirt. Articulated rods were used in the Goshawk engine, but were not embodied in the later Rolls-Royce Merlin, for which Arthur Rowledge had designed a revised blade and fork system.
  Later production R engines featured sodium-filled exhaust valve stems for improved cooling, while additional modifications included a redesigned lower crankcase casting and the introduction of an oil scraper ring below the piston gudgeon pin; a measure that was carried over to the Merlin engine. A balanced crankshaft was introduced in May 1931, and the compression ratio on the "sprint" engines prepared for that year was raised from 6:1 to 7:1.
  The ignition system consisted of two rear-mounted, crankshaft-driven magnetos, each supplying one of a pair of spark plugs fitted to each cylinder. This is common practise for aero engines, as it ensures continued operation in the case of a single magneto failure, and has the advantage of more efficient combustion over a single spark plug application.
caption: Sectioned view of a Rolls-Royce Merlin featuring wet-liner cylinders and lower oil scraper rings, both originally developed for the R engine
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