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, which was never flown, 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 Griffon 37.V.12 was originally developed to meet Fleet Air Arm requirements specifically, to give high powers at low altitudes and thus to be suitable for installation in torpedo-bombers. The decision to go ahead with it was taken in December 1939, and it was recognized that the same basic engine should be suitable for installation in existing fighters, then powered with the Merlin.
On 8 November 1939 N E Rowe of the Air Ministry suggested fitting the Griffon in a Spitfire. Three weeks later permission was given to Supermarine to explore the possibilities of adapting the Griffon to the Spitfire; in response Supermarine issued 'Specification 466' on 4 December. This decision led to a change in the disposition of the engine accessories to reduce the frontal area of the engine as much as possible. As a result the frontal area of the bare Griffon engine was 7.9 square feet (0.73 m2) compared with 7.5 square feet (0.70 m2) of the Merlin. This redesigned engine first ran on 26 June 1940 and went into production as the Griffon II.
In early-1940, on the orders of Lord Beaverbrook, Minister of Aircraft Production, work on the new engine had been halted temporarily to concentrate on the smaller 27 L (1,650 cu in) Merlin and the 24 cylinder Vulture which had already surpassed the output achieved with the early Griffon.
Relative frontal areas were 7.5 sq ft and 7.9 sq ft. "It would seem well-nigh impossible," Flight remarked, when describing the Griffon for the first time, "that with such similarity of overall dimensions in two engines of the same basic type the swept volume of one should be 35.9 per cent larger than that of the other. Piston area of the Griffon is 23 per cent greater than that of the Merlin, this having been achieved by increasing the cylinder bore to 6in."
Though following Merlin lines, the Griffon differed very extensively in detail design. A prominent innovation was the taking of the camshaft and magneto drives from the front; this was decided upon in order to reduce torsional vibration in the camshaft drive. By interpolating a semi-floating coupling between the crankshaft and the driving wheel of the reduction gearing, and, in addition, by taking the cam drives from the airscrew-driving gear, angular variations in crankshaft speed were greatly reduced in their transmission to the camshafts.
A feature of the crank assembly is that the main bearings and big ends are all lubricated from the hollow interior of the shaft.
In 1938 the Fleet Air Arm approached Rolls-Royce and asked whether a larger version of the Merlin could be designed. The requirements were that the new engine have good power at low altitude and that it be reliable and easy to service. Work began on the design of the engine soon afterwards. The design process was relatively smooth compared with that of the Merlin, and the first of three prototype Griffon Is first ran in the Experimental Department on 30 November 1939.
Compared with earlier Rolls-Royce designs, the Griffon engine featured several improvements which meant it was physically only slightly larger than the Merlin, in spite of its 36% larger capacity of 37 litres (2,260 cu in). One significant difference was the incorporation of the camshaft and magneto drives into the propeller reduction gears at the front of the engine, rather than using a separate system of gears driven from the back end of the crankshaft; this allowed the overall length of the engine to be reduced as well as making the drive train more reliable and efficient. The Griffon was the first Rolls-Royce production aero engine to use a hollow crankshaft as the means of lubricating the main and big end bearings, providing a more even distribution of oil to each bearing. In another change from convention, one high efficiency B.T.H-manufactured dual magneto was mounted on top of the propeller reduction casing; earlier Rolls-Royce designs using twin magnetos mounted at the rear of the engine.
First run in November 1939, early Griffons-the II, III and IV-had two-speed, single stage blowers, and gave a maximum power of 1,735 h.p. at 16,000 ft and 1,495 h.p. at 14,500 ft. For take-off 1,720 h.p. was available. These engines differed in reduction gear ratio, the II and III being geared 0.451:1, and the 4, 0.510:1. Until superseded by the Griffon XII the series II engine was installed in the Firefly I and II; the Griffon III and IV were mounted in the clipped-wing Spitfire XII specially developed to tackle the Fw 190 at low and medium levels. By increasing boost pressure to 15 lb/sq in the take-off power of the Griffon VI was raised to 1,815 h.p., an increment of importance in that this engine powered the Seafire XV and XVII carrier-borne fighters. The Griffon XII resembled the VI except in supercharger and reduction gear ratios; it delivered 1,645 h.p. at 11,500 ft.
The system of designating the two-stage supercharged Merlins with series numbers beginning with 6 was also adopted for the Griffon range. For a weight increase of 290 lb, accounted for by the new blower system, the Griffon 61 delivered 2,035 h.p. at 7,000 ft and 1,820 h.p. at 21,000 ft; its most famous application was in the Spitfire 21. Identical in all but reduction gear, the Griffon 65 powered the Spitfire XIV, and the Griffon 66 was again similar but had a cabin supercharger for P.R. work in the Spitfire XIX. Griffons 64 and 67 were derived, respectively, from the 61 and 64, and gave no less than 2,375 h.p. at 1,250ft, and 2,145 h.p. at 15,500 ft; the 64 powered the Spitfire 21 and Seafire 46, and the 67 appeared in the Spitfire XIV.
The Griffon 61 series introduced a two stage supercharger and other design changes: the pressure oil pumps were now housed internally within the sump and an effort was made to remove as many external pipes as possible. In addition, the drive for the supercharger was taken from the crankshaft at the back of the engine, via a short torsion shaft, rather than from the front of the engine, using a long drive shaft as used by earlier Griffon variants.
Though early examples of the Vickers-Supermarine Spiteful had the Griffon 61, the production model had the Griffon 69, the maximum power of which exceeded that of the earlier two stage Griffons by some 300 h.p., with no increase in weight. Official maximum powers were 2,375 h.p. at 1,250ft in M.S. gear, and 2,130 h.p. at 15,500 ft in F.S. gear. Boost pressure was plus 25 lb/sq in, made possible by 150 grade fuel.
Griffons 72 and 74 were further developments of the 65 for the Fleet Air Arm; they delivered 2,245 h.p. at 9,250ft. The 74 was distinguished from the 72 in having a Rolls-Royce injection pump instead of the Rolls-Royce Bendix/Stromberg carburettor. These engines were, respectively, the power plants of the prototype Firefly IV and production Fireflies of the same mark.
Basic component overview - Griffon 65
An innovation of more than usual interest was the adoption, on the Griffon 85, of a drive for contra-rotating airscrews; this engine appeared in the Spitfire XIV, 21 and Seafire 45. The Griffon 87 was a further development, rated at 2,145 h.p. maximum at 15,500 ft, and the 88 differed only in having an injection pump. "Contraprop" Griffons, of the 85, 87 and 88 series, were mounted in the Spitfire XIV and 21, and Seafire 45 and 47.
For the Barracuda V Rolls-Royce developed the Griffon 37, with a modified two-speed, single-stage blower, maintaining 18 lb/sq in boost in either gear. Though the Barracuda was provided with 2,055 h.p. at 2,250 ft, only Merlin powered machines of this type went into squadron service.
The most impressive of all Griffon developments was the three-stage supercharger incorporated in the 101 series, together with Rolls-Royce fuel injection. The new blower made possible an output of over 2,000 h.p. up to 20,000 ft with no increase in dimensions. Weight rose by 40 lb.
Notable among post-war developments is the Griffon 67, for use in long-range Service aircraft and having provision for contra-rotating airscrews. On this engine water/methanol injection is automatically brought into play when the boost pressure for the standard fuel approaches maximum value. The controlling unit works in conjunction with the boost control and progressively increases the flow of water methanol with boost pressures from 18.5 to 25 lb/sq in. Contraprop Griffons power the Avro Shackleton maritime-reconnaissance aircraft. Other variants of the Griffon are serving in the numerous marks of Fairey Firefly.
Unlike the Merlin, the Griffon was designed from the outset to use a single-stage supercharger driven by a two-speed, hydraulically operated gearbox; the production versions, the Griffon II, III, IV, and VI series, were designed to give their maximum power at low altitudes and were mainly used by the Fleet Air Arm. The Griffon 60, 70, and 80 series featured two-stage supercharging and achieved their maximum power at low to medium altitudes. The Griffon 101, 121, and 130 series engines, collectively designated Griffon 3 SML, used a two-stage, three-speed supercharger, adding a set of "Low Supercharger (L.S)" gears to the already existing Medium and Full Supercharger (M.S and F.S) gears. Another modification was to increase the diameters of both impellers, thus increasing the rated altitudes at which maximum power could be generated in each gear. While the 101 continued to drive a five-blade propeller, the 121 and 130 series were designed to drive contra-rotating propellers. In 1946 a Griffon 101 was fitted to the Supermarine Spiteful XVI, RB518 (a re-engined production Mk.XIV); this aircraft achieved a maximum speed of 494 mph (795 km/h) with full military equipment.
The Griffon was the last in the line of V-12 aero engines to be produced by Rolls-Royce with production of the aero version ceasing in December 1955 after 8,108 were built, the Griffon 130 being the last in the series. Griffon engines remained in Royal Air Force service with the Battle of Britain Memorial Flight and power the last remaining airworthy Avro Shackleton.
A marine version, the Sea Griffon, continued to be produced for the RAF's High Speed Launches.
Several North American Mustangs raced in the Unlimited Class races at the Reno Air Races have been fitted with Griffons. These include the RB51 Red Baron (NL7715C), "Precious Metal" (N6WJ) and a Mustang/Learjet hybrid "Miss Ashley II" (N57LR). In all cases, Griffons with contra-rotating propellers, taken from Avro Shackleton patrol bombers were used in these aircraft. The RB51 Red Baron is noteworthy for holding the FAI piston-engine 3-kilometer world speed record from 1979 to 1989.
In 1965, SFR Yugoslavia used Griffon engines as the main power unit for their first domestically produced self-propelled artillery system, the S65, but the system was withdrawn from service in the early 1980s, because of poor fuel economy.
The 1980 Miss Budweiser Unlimited Hydroplane dominated the race circuit with a Rolls-Royce Griffon engine. It was the last of the competitive piston-engined boats, before turboshaft powerplants took over.
In modern day tractor pulling, Griffon engines are also in use, a single or double, rated each at 3,500 hp (2,600 kW).
Type: 12-cylinder supercharged liquid-cooled 60° Vee aircraft piston engine