Rolls-Royce R

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.

Origin
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.

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 oil scraper 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.

Cooling
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.

Supercharger and fuel
The keys to the R engine's high power-to-weight ratio were its supercharger design, ability to run at high revolutions due to its structural strength, and the special blends of fuel used. The double-sided supercharger impeller was a new development for Rolls-Royce: running at a ratio of almost 8:1, it could supply intake air at up to 18 pounds per square inch (psi) (1.24 bar) above atmospheric pressure, a figure known as "boost" and commonly abbreviated as "+x lb". 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.

On an early test run the R engine produced 1,400 hp (1,040 kW) and was noted to idle happily at 450 revolutions per minute (rpm). With increased boost ratings and fuel developed by Banks, the R engine ultimately developed 2,530 hp (1,890 kW) at 3,200 rpm; well over double the maximum power output of the Buzzard. 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.

Ground testing
The first run of engine R1 took place at Rolls-Royce's Derby factory on 7 April 1929 with R7 running the next day. Many mechanical failures were experienced during bench testing including burnt valves, connecting rod breakages and main bearing seizures, 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, but the continual redesigning and testing of components reduced all these problems. Unknown to Royce himself, the engineers had also fitted "Wellworthy" pistons that were better able to withstand the 13 tons "pressure" of each firing stroke.

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. Development time was short and the deafening sound of three Kestrels and an R engine running at high power for 24 hours a day took its toll on the local population. The Mayor of Derby stepped in and asked that the people endure the noise for the sake of British prestige; subsequently testing continued for seven months.

In the course of a 25-minute test an early R engine would consume 60 Imperial gallons (gal) (270 L) of pre-heated castor oil. The majority of this was spat out of the exhaust ports and smothered the test cell walls, milk being given to staff to minimise the effects of this well-known laxative. Up to 200 gal (900 L) of the special fuel blend had to be mixed for each test, 80 gal (360 L) of which were used just to warm the engine to operating temperature. The same coarse-pitch propeller used for flight trials was fitted throughout these tests.

Flight testing
Overseen by Cyril Lovesey, flight testing commenced on 4 August 1929 in the new Supermarine S.6 at RAF Calshot, a seaplane and flying boat station on Southampton Water in Hampshire. 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.

Relationship to the Griffon and Merlin
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, was used for "Moderately Supercharged Buzzard development" (which was not proceeded with until much later), and bore no direct relationship to the volume-produced Griffon of the 1940s.

The pre-production Griffon I shared the R engine's bore and stroke, 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:

"Quite simply the R-type engine was far ahead of its time, a marvel of British skill and ability."

- Steve Holter

Schneider Trophy use
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 328.63 mph, 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 400 hp to 2300 hp. 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 Flight" was wound up within weeks of the 1931 win as there were to be no more Schneider Trophy contests. 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.

World speed record use
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.

Airspeed record
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. 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.
 * Supermarine S.6
 * Supermarine S.6B

Land speed record
Sir Malcolm Campbell, and later his son Donald, used R engines from 1931 to 1951. At Sir Malcolm's knighthood ceremony in February 1931, King George V expressed great interest in the R and asked many questions about its fuel consumption and performance.
 * Campbell-Railton Blue Bird

In 1932, Campbell stated that he "... was fortunate in procuring a special R.R. Schneider Trophy engine" for his land speed record car to replace its Napier Lion. Lent to him by Rolls-Royce, this engine was either R25 or R31. By February 1933 the car, named Blue Bird had been rebuilt to accommodate the larger engine and was running at Daytona.

In late 1933 Campbell bought engine R37 from Rolls-Royce; and had also been lent R17 and R19 by Lord Wakefield, and R39 by Rolls-Royce. He then lent R17 to George Eyston. Once he had achieved the 300 mi/h record on 3 September 1935 at the Bonneville Speedway, Campbell retired from further land speed endeavours.

Lord Wakefield arranged for a replica of the Rolls-Royce R to be exhibited at the 1933 Motor Show, held at Olympia, London. A press report from the event provides an insight into the public perception of the engine:

"Of the size only of an office desk ... this 12-cylinder supercharged racing engine is more powerful than an express locomotive. Its design is stated to be so valuable that it is still on the Government's secret list."

- Press report

Blue Bird is now on display at the Daytona International Speedway. During the mid-1930s, George Eyston set many speed records with his Speed of the Wind car, powered by an unsupercharged Rolls-Royce Kestrel. In 1937 he built a massive new car, Thunderbolt, powered by two R engines to attempt the absolute land speed record. At first Eyston experienced clutch failure due to the combined power of the engines. Nevertheless, he took the record in November 1937, reaching 312 mph (502 km/h), and in 1938 when Thunderbolt reached 357.5 mph (575 km/h). When first built at Bean Industries in Tipton, the nearside engine fitted to Thunderbolt was R27 which had powered S1595 when it set the air speed record in 1931. The other was R25, used by the same aircraft to win the Schneider Trophy two weeks earlier. Eyston had also borrowed R17 from Sir Malcolm Campbell and, with the continuing support that Rolls-Royce extended to both Campbell and Eyston, he also had the option of using R39.
 * Thunderbolt

Water speed record
Two R engines, R17 and R19, were built for Sir Henry Segrave's twin-engined water speed record boat Miss England II, this craft being ready for trials on Windermere by June 1930. On Friday 13 June, Segrave was fatally injured and a Rolls-Royce technical advisor, Victor Halliwell, was killed when Miss England II capsized at high speed after possibly hitting a log. Shortly before his death Segrave learnt that he had set a new water speed record of just under 100 mph (160 km/h). On 18 July 1932, Kaye Don set a new world water speed record of 119.81 mph on Loch Lomond in a new boat, Miss England III, which also used engines R17 and R19.
 * Miss England II and III

In late 1935, Sir Malcolm Campbell decided to challenge the water speed record. At that point he had two Napier Lions and one Rolls-Royce R engine, R37 at his disposal, and it was decided to install the R engine in Blue Bird K3. During trials on Loch Lomond in June 1937 the engine was "slightly damaged ... because of trouble with the circulating water system". In August 1937 Blue Bird K3 was taken to Lake Maggiore in Italy where "the modified [circulation] system worked perfectly with a second engine", R39.
 * Blue Bird K3

R39 was again used in 1939 in Blue Bird K4. In 1947 Campbell unsuccessfully converted K4 to jet power using a de Havilland Goblin engine. After Campbell's death from natural causes in 1948, Donald Campbell bought K4 for a nominal sum as well as the 1935 record car when his father's effects were auctioned. He also purchased R37 back from a car dealer and reinstalled it in K4. Attempts on the record were made in 1949, and again in 1951 when R37 was "damaged beyond any immediate repair" by overheating. Another attempt was made later in the year using R39, but K4 suffered a structural failure and sank in Coniston Water. It was recovered and broken up on the shore.
 * Blue Bird K4 and the work of Leo Villa

The care and maintenance of the Campbell's R engines was entrusted to Leo Villa, a Cockney born to a Swiss father, who was described as "the man behind the Campbells" and a central figure who "fitted the first nut to the first bolt". Villa learnt his trade of "aircraft mechanic" in the Royal Flying Corps; his first job was fitting Beardmore 160 hp engines to airframes. After World War I he worked for a motor racing company and participated as co-driver and mechanic in several races.

Villa was first employed by Malcolm Campbell in 1922, and continued in the service of Donald Campbell until 1967, when Campbell was killed during a record attempt on Coniston Water. He was the chief caretaker of their R engines until the last R-powered record attempt in 1951, after which his responsibilities centred on Campbell's jet engines. Villa's many responsibilities included installing and removing the engines, repairing and tuning them, and operating the compressed air and magneto for starting them. During the World War II years, he was responsible for the upkeep of Blue Bird K4 and the spare R engines, but unknown to him they had been sold along with K3. Villa eventually took the three R engines to Thomson & Taylor at Brooklands for long-term storage.

His relationship with Malcolm Campbell was strained at times: Campbell, with no engineering background, would often question Villa's intimate knowledge of the R engine, but his relations with Donald Campbell were much better, as they were of a similar age. At Lake Garda in 1951 Villa noted the willingness of "Don" to help with engineering tasks, and the difficulties of working on the R engine:

"I was in the workshop stitching the old R37 back together and had the long job of lapping in all 48 valves. It was a terrible job because the engine was two monoblocs, which meant that you couldn't just lift off the heads, you had to lift what amounted to two separate engines and even then getting the valves in was no easy task. But old Don just rolled up his sleeves and mucked in."

- Leo Villa

World speed record summary


Note:
 * Air speed record
 * Supermarine S.6: 8 September 1929 – 355.8 mph (572.6 km/h)
 * Supermarine S.6B: 29 September 1931 – 407.5 mph (656 km/h)


 * Land speed record
 * Blue Bird: 3 September 1935 – 301 mph (484 km/h)
 * Thunderbolt: 16 September 1938 – 357.5 mph (575 km/h)


 * Water speed record
 * Miss England II: 9 July 1931 – 110.28 mph (177.48 km/h)
 * Miss England III: 18 July 1932 – 119.81 mph (192.82 km/h)
 * Blue Bird K3: 17 August 1938 – 130.91 mph (210.67 km/h)
 * Blue Bird K4: 19 August 1939 – 141.74 mph (228.11 km/h)

Production summary
Nineteen R engines were produced at Derby between 1929 and 1931, all given odd serial numbers. This was a Rolls-Royce convention when the propeller rotated anticlockwise when viewed from the front, but an exception was made for R17, the sole clockwise-rotation R engine. There is some confusion as to whether 19 or 20 R engines were produced. In his notes Leo Villa refers to an R18 engine, but according to Holter this may have been R17 converted to clockwise rotation at the request of Malcolm Campbell rather than an additional example. There was no R13 as Rolls-Royce never used the number 13 in any of their designations. A summary production list is given below:


 * 1929 Development engines
 * R1, R3 and R5


 * 1929 Schneider Trophy engines
 * R7, R9 and R15


 * 1930 Development engine
 * R11


 * 1930 Wakefield order for Miss England II
 * R17 and R19


 * 1931 Schneider Trophy engines
 * R21, R23, R25, R27, R29 and R31


 * 1931 Development/factory spare engines
 * R33, R35, R37 and R39

Applications

 * Aircraft
 * Supermarine S.6
 * Supermarine S.6A
 * Supermarine S.6B
 * Cars
 * Campbell-Railton Blue Bird
 * Thunderbolt
 * Boats
 * Blue Bird K3
 * Blue Bird K4
 * Miss England II
 * Miss England III

Engines on display
The Royal Air Force Museum London at Hendon has a Rolls-Royce R on display (museum number 65E1139) that came to the museum in November 1965 from RAF Cranwell. According to the museum's records, before that it was with George Eyston as one of Thunderbolt's record engines. Its data plate states that it is R25 under Air Ministry contract number A106961 which makes it the second 1931 race engine delivered to RAF Calshot. The London Science Museum has an R engine on display which is catalogued as a stand-alone item, inventory number 1948-310. This is R27, the second sprint engine prepared for the successful air speed record attempt, and later used in Thunderbolt. The Science Museum also has S.6B, S1595, (winner of the 1931 race and the final air speed record aircraft) on display. The Filching Manor Motor Museum has R37 which is destined to be fitted in its restoration of the Blue Bird K3 water speed record boat.
 * R25
 * R27
 * R37

These three engines are the only ones listed by the British Aircraft Preservation Council/Rolls-Royce Heritage Trust. The Solent Sky museum's S.6A, N248, (a competing aircraft in the 1929 race as an S.6, and stand-by for the 1931 race, modified as an S.6A) does not contain an R engine.