Rolls-Royce R

1929 British aero engine

The Rolls Royce R is a British aero engine that was 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 (2,240 cu in) capacity, supercharged V 12 capable of producing just under 2,800 horsepower (2,090 kW), and weighed 1,640 pounds (770 kg). 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 (640 km/h). 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. The experience gained by Rolls Royce and Supermarine designers from the R engine was invaluable in the subsequent development of the Rolls Royce Merlin engine and the Spitfire. A de rated R engine, known as the Griffon, was tested in 1933, but it was not directly related to the production Rolls Royce Griffon of 1939, of the same exact bore/stroke and resultant displacement figures as the "R" design. Three examples of the R engine are on public display in British museums as of 2014.

Rolls Royce realised that the Napier Lion engine used in the 1927 Supermarine S.5 Schneider Trophy winner had reached the peak of its development, and that for Britain's entrant in the next race to be competitive a new, more powerful engine design was required. The first configuration drawing of the "Racing H" engine, based on the Buzzard, was sent to R. J. Mitchell of Supermarine on 3 July 1928, allowing Mitchell to start design of the new S.6 Schneider Trophy seaplane. Shortly after this the engine's name was changed to R for "Racing". An official British Government contract to proceed with the project was not awarded until February 1929, leaving Rolls Royce six months to develop the engine before the planned Schneider Trophy competition of that year.|group=nb

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;

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. 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.

Cooling this large engine whilst minimising aerodynamic drag posed new challenges for both the Rolls Royce and Supermarine design teams. Traditional cooling methods using honeycomb type radiators were known to cause high drag in flight; consequently it was decided to use the surface skins of the S.6 wings and floats as heat exchangers, employing a double skinned structure through which the coolant could circulate. Engine oil was cooled in a similar manner using channels in the fuselage and empennage skins. The S.6 was described at the time as a "flying radiator", and it had been estimated that this coolant system dissipated the equivalent of 1,000 hp (745 kW) of heat in flight. However, even with this system in use, engine overheating was noted during the race flights, requiring the pilots to reduce the throttle setting to maintain a safe operating temperature. A not so obvious cooling measure was the deliberate use of a rich fuel mixture, which accounts for the frequent reports of black smoke seen issuing from the engine exhaust stubs. Although this robbed the engine of some power, it increased reliability and reduced the possibility of detonation in the cylinders. By comparison the maximum boost of the earlier Rolls Royce Kestrel design was +6 lb (0.4 bar), this figure not being achieved until 1934. The high boost pressures initially caused the spark plugs to fail on test, and eventually the Lodge type X170 plug was chosen as it proved to be extremely reliable. The development of special fuel was attributed to the work of "Rod" Banks, an engineer who specialised in fuels and engine development. After using neat benzole for early ground test runs, a mixture of 11% aviation petrol and 89% benzole plus 5 cubic centimetres (cc) of tetra ethyl lead per Imperial gallon (4.5 L) was tried. This blend of fuel was used to win the 1929 Schneider Trophy race, and continued to be used until June 1931. It was discovered that adding 10% methanol to this mixture resulted in a 20 hp (15 kW) increase, with the further advantage of reduced fuel weight – particularly important for aircraft use – due to its lowered specific gravity. For the 1931 airspeed record attempt acetone was added to prevent intermittent misfiring; the composition of this final blend was 30% benzole, 60% methanol, and 10% acetone, plus 4.2 cc of tetra ethyl lead per gallon. The engine was further tested and cleared for limited sprint racing at 2,783 hp (2,075 kW) at 3,400 rpm and +21 lb (1.45 bar) of boost, but this capability was not used due to concerns with the S.6B's airframe not being able to withstand the power, and the inability of the aircraft to lift the extra fuel required to meet the increased consumption.

The first run of engine R1 took place at Rolls Royce's Derby factory on 7 April 1929 with R7 running the next day. while considerably more trouble than expected occurred with valve springs; at one time two or three would be found broken after a 10 minute run,

Ground testing of the R involved the use of three Kestrel engines: one to simulate a headwind or airspeed, one to provide ventilation of the test area, and another to cool the crankcase. Superchargers could be tested on a separate rig that was driven by another Kestrel engine. Eight men were required to run a test cell, led by the "Chief Tester" who had the tasks of logging the figures and directing the other operators. One of these chief testers was Victor Halliwell who later lost his life whilst on board the water speed record contender Miss England II. The conditions in the test cell were particularly unpleasant; deafness and tinnitus lasting up to two days were experienced by test personnel even after plugging their ears with cotton wool. During pre race scrutineering tests, metal particles were found on two of the engine's 24 spark plugs indicating a piston failure which would require an engine re build or replacement. The competition rules did not allow an engine change, but due to the foresight of Ernest Hives, several Rolls Royce engineers and mechanics that were familiar with the R had travelled down to Southampton to witness the trials, and with their assistance one cylinder bank was removed, the damaged piston replaced and the cylinder refurbished. This work was completed overnight and allowed the team to continue in the competition. Engine starting was achieved by a combination of compressed air and a hand turned magneto; however, starting problems were encountered during pre race testing at Calshot due to moisture in the air and water contamination of the fuel. A complicated test procedure was devised to ensure clean fuel for competition flights since more than 0.3% water content made it unusable. As expected, minor engine failures continued to be experienced, and to counter this engines and parts were transported at high speed between Derby and Calshot using an adapted Rolls Royce Phantom I motor car. Travelling mostly after dark, this vehicle became known as the Phantom of The Night.

According to Arthur Rubbra's memoirs, a de rated version of the R engine, known by the name Griffon at that time, was tested in 1933. This engine, R11, but was otherwise a completely new design that first ran in the Experimental Department in November 1939. Although this single engine was never flown, the production version, the Griffon II, first flew in 1941 installed in the Fairey Firefly. A significant difference between the R and the production Griffon was the re location of the camshaft and supercharger drives to the front of the engine to reduce overall length. Another length reducing measure was the use of a single magneto (the R had two, mounted at the rear), this again was moved to the front of the engine. Further possible development work on the R engine was discussed in The National Archives' file AVIA 13/122, which contains a proposal from the Royal Aircraft Establishment dated October and November 1932, to test four engines to destruction. This document states that there were five engines available for test purposes, the fifth to be used for a standard Type Test at high revolutions. Although not directly related to the Spitfire, the Supermarine engineers gained valuable experience of high speed flight with the S.5 and S.6 aircraft, their next project being the Rolls Royce Goshawk powered Supermarine Type 224 prototype fighter aircraft. Technological advances used in the R engine, such as sodium cooled valves and spark plugs able to operate under high boost pressures, were incorporated into the Rolls Royce Merlin design. The author Steve Holter sums up the design of the Rolls Royce R with these words:

The Schneider Trophy was a prestigious annual prize competition for seaplanes that was first held in 1913. The 1926 race was the first where all the teams fielded pilots from their armed forces, the Air Ministry financing a British team known as the High Speed Flight drawn from the Royal Air Force. Sometimes known simply as The Flight, the team was formed at the Marine Aircraft Experimental Establishment, Felixstowe, in preparation for the 1927 race in which Supermarine's Mitchell designed, Napier Lion powered Supermarine S.5s placed first and second. 1927 was the last annual competition, the event then moving onto a biannual schedule to allow more development time between races. During the 1929 race at Cowes between Great Britain and Italy, Richard Waghorn flying the Supermarine S.6 with the new Rolls Royce R engine retained the Schneider Trophy for Great Britain with an average speed of , and also gained the 50 km and 100 km (31 mi and 62 mi) world speed records. The records were subsequently beaten when Richard Atcherley later registered higher speeds when he completed his laps of the circuit. The Italian team placed second and fourth using Fiat AS.3 V 12 powered Macchi M.52 aircraft. Another racing seaplane, the Fiat C.29 powered by the AS.5 engine attended the contest but did not compete. More comparable to the R engine was the Fiat AS.6 engine developed for the 1931 contest; effectively a coupled, double AS.5 that suffered from technical problems. With the assistance of Rod Banks, the AS.6 powered the Macchi M. C.72 to a new speed record for piston powered seaplanes in 1934 of 440.6 mph (709.2 km/h), a record that still stands as of 2009. In 1931 the British Government withdrew financial support, but a private donation of £100,000 from Lucy, Lady Houston allowed Supermarine to compete on 13 September using the R powered Supermarine S.6B. For this race the engine's rating was increased by to The Italian and French entrants however, failed to ready their aircraft and crews in time for the competition, and the remaining British team set both a new world speed record at 379 mph (610 km/h) and, unopposed, won the trophy outright with a third consecutive victory. The original Trophy is on display in the London Science Museum along with the S.6B that secured it, as well as the R engine that powered this aircraft for the subsequent airspeed record flight.

New airspeed records were set after the 1929 and 1931 Schneider Trophy contests, both achieved using the R engine. In the two decades before World War II, the quest to break the land speed record was hotly contested, particularly so in the early 1930s. Aero engines were often used to power wheeled vehicles to ever higher speeds, chosen because of their high power to weight ratios: the Liberty engine, Napier Lion and the Sunbeam Matabele were among the engine types used in the 1920s. The Rolls Royce R was the latest development in high powered aero engine design at the time, and was chosen by several makers of land speed record contending cars; the engine was also chosen for powerboats attempting the water speed record. One car and two boats successfully used the combined power of two R engines.

Supermarine S.6
Immediately after the 1929 Schneider Trophy contest Squadron Leader Augustus Orlebar, commanding officer of the High Speed Flight, set a new airspeed record of 355.8 mph (572.6 km/h) using Supermarine S.6, N247. Supermarine S.6B
On 29 September 1931, barely two weeks after the British team had secured the Schneider Trophy outright, Flight Lieutenant George Stainforth broke the world airspeed record in a Rolls Royce R powered Supermarine S.6B, serial S1595, reaching an average speed of 407.5 mph (655.67 km/h). It had been intended to also use the identical sister aircraft, S1596, for the attempt but Stainforth had capsized it on 16 September whilst testing a propeller.