The "Spitfire" & "Hurricane" Rolls-Royce Engines

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The Rolls-Royce Merlin

The Rolls-Royce Griffon

The Rolls-Royce Merlin

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By 1932 it was becoming apparent to Rolls-Royce that their best-selling engine, the 21.2 litre 745HP Kestrel was coming towards the end of its development life. A decision was made by Sir Henry Royce to develop a new engine using some of the experience of the Schneider Trophy winning 'R' engine. It retained the V12 configuration and geared supercharger of its predecessors, but was of 27 liters swept volume. It was anticipated initially that this engine would be able to reliably deliver around 1000HP. The engine was known initially as PV12 (Private venture, development initially entirely funded by Rolls-Royce). When in October 1933 the Air Ministry agreed to finance the development, it was named Merlin (Rolls-Royce piston engines were by convention named after birds of prey, jets after rivers). The firing order of the cylinders was 1A, 6B, 4A, 3B, 2A, 5B, 6A, 1B, 3A, 4B, 5A, 2B (where A is on the right viewed from the pilots seat- B on the left- and the rows are numbered with the front row being 1).

Ironically, in view of its later reputation of extreme reliability, the early development of the engine was plagued with problems, with gear train failures and persistent failures of the water jackets (the cooling mixture eventually became 30% glycol as antifreeze in water at +18PSI pressure). Eventually in July 1934 the Merlin passed its type testing and was rated at 790HP at 12 000 feet at 2500 RPM. The Merlin B was tried with a ramp head to the cylinder which had improved fuel mixing and flame propagation in Rolls auto engines, and in February 1935 delivered 950HP at 11000 feet equivalent. Based on their experiences, Rolls-Royce decided to make the crankcase and cylinder blocks as 3 separate castings, with bolt-on ramp heads to the cylinders. This engine was the Merlin C. By this time the promise of a low-profile aero engine of 1000HP had persuaded both RJ Mitchell and Sydney Camm to base their designs around this new untried engine. This engine still had problems, but after some modifications as Merlins E and F, a Merlin E passed a civil 50 hour Type Test at 955HP (maximum 1045HP). As an emergency measure it was decided to scale up the parallel cylinder head as used in the Kestrel to the larger engine (Merlin G). This engine easily passed its Type Test a month before the F (now released as Merlin I) and was then designated Merlin II. This engine weighed 1335lb and was rated at a maximum power of 1030HP at 3000RPM at 16250 feet, and ran on 87 octane fuel. It is worthy of note that in 1937 an attempt was made to break the World Landplane Speed Record, using a highly modified Spitfire I and a specially strengthened Merlin II. This engine actually generated 2160HP, and showed the potential for development of the engine. Most of the modifications developed for this engine eventually found their way into production Merlins. The Merlin III was adapted for the use of a constant-speed propeller and a constant-speed unit.
A variant of this engine with a higher supercharger gearing (providing up to 12.5lb boost) and a Coffman cartridge starter was termed the XII and marked the difference between the Spitfire I and II.

In 1935, after problems with supercharger gearing, Rolls-Royce decided to take out a license for the Farman 2-speed drive. The advantage of the 2-speed supercharger was that it could be run at low speed, using little energy, in the thick lower altitudes, while being available to enrich the air supply at altitude. There are supercharged engines providing zero extra boost at sea level being flown today. The first of these engines with a 2-speed supercharger was the Merlin X. This added significantly to the length of the engine.

In 1939 a decision was made to focus on 100 octane fuel for aero engines. This fuel permitted higher boost pressures and temperatures without detonation, and allowed the use of +12lb boost rather than the previous limit of +6lb.

The next major development of the Merlin came from Sir Stanley Hooker. It was realized in the development of the Merlin for the World Speed attempt that the efficiency of the Merlin supercharger was relatively poor. Hooker, a mathematician by trade, examined the supercharger from first principles, and markedly improved its efficiency. He also improved the flow characteristics of the air inlet, which improved the output power at altitude. Although the original installation was elongated even further, it was found that by turning the carburetor around the length was similar to the original installation. This new engine was the Merlin XX, and allowed power to be maintained at much higher altitudes (1175HP at 20 000 feet compared to 1160HP at 13 500 feet for the Merlin II). The single-speed supercharger Merlin 45 incorporated many of these modifications, and this engine, fitted to the Spitfire airframe, became the Mark V Spitfire.

Some of these engines were modified for low-altitude power, since most of the air combat was taking place around 6 000 feet. In these, the supercharger impellers were shortened, and the speed of the constant-speed unit increased. This gave a maximum power height of around 6 000 feet, and increased speed by around 22 mph at this height. If coaxed to higher altitudes, however, the engine suffered badly.

The development of high-altitude bombers required the development of an engine with a higher full-throttle height. Rather than move to turbochargers, Hooker suggested adding two superchargers in series. Since a high altitude supercharger of the right size had already been developed, the output from the Rolls-Royce Vulture supercharger was simply fed into the supercharger of a Merlin 46. The only modification required was the incorporation of a cooling stage after the two supercharger stages to prevent premature fuel detonation during compression in the cylinders. The new engine, the Merlin 60, had a full-throttle height of nearly 30 000 feet. A redesign changed the supercharger gearing and introduced a 2-piece cylinder block to produce the Merlin 61. This engine produced spectacular effects when fitted to a Spitfire. Although intended for the Mark VIII, it was possible to fit it to the Mark V airframe, and this became the Spitfire Mark IX/XVI series. The extra cooling necessary became evident by the enlarged radiator under the left wing.

As the specific power from the engines increased, the focus of much of the design was strengthening. An empirical approach was to run an engine at high power until something broke, then strengthen or redesign that part and carry on. The consequence of these developments was the Merlin 130 with a low level power of 2030HP, and an elevation of the height at which 1000HP was available from 16 000 to 36 000 feet. In late 1944 a Merlin was run for 15 minutes at 2640HP! After the difficult beginnings the ability of the Merlin to withstand abuse became a watchword. Few engines tolerate full power loads for any great period, but there are examples on record of Lancaster pilots losing one of their Merlins shortly after takeoff, but simply continuing the mission with all the remaining throttles pushed to the stops. The engines rarely failed.

The 500, 600, and 700 series Merlins were mostly post-War developments for civilian transports. In these the focus was not on absolute power but on component life. In total the production run on the Merlin was 168 040.

The Carburetor Design

One of the great problems as discerned by pilots was the tendency for the carbureted engine to cut out under negative 'g'. Luftwaffe pilots learned to escape by simply pushing the nose of their aircraft down into a dive, as their fuel- injected engines did not cut out under these circumstances. Many authors have criticized this aspect of the Merlin design. In reality, like most engineering, it resulted from a design compromise- the drop in temperature developed in a carburetor results in an increase in the density of the fuel-air mixture when compared to that of a fuel injection system. As a consequence the Merlin produced a higher specific power output (horse power per pound) that the equivalent German engine. It was felt that this gave a higher power to weight ratio for the fighter and (rightly or wrongly) that this outweighed the disadvantages. By 1941 Miss Tilly Shilling in Farnborough had developed a partial cure for the problem. A diaphragm across the float chambers with a calibrated hole (the infamous "Miss Shilling's orifice"!) allowed negative 'g' maneuvers, and was fitted as standard from March 1941. Sustained zero 'g' maneuvers were not sorted out until somewhat later. In 1942 an anti-g version of the SU carburetor was fitted to single and two-stage Merlins. 1943 saw the introduction of the Bendix-Stromburg carburetor which injected fuel at 5psi through a nozzle direct into the supercharger and was fitted to the Merlins 66, 70, 76, 77, and 85. The final development was the SU injection carburetor which injected fuel into the supercharger using a fuel pump driven as a function of crankshaft speed and engine pressures, which was fitted to the 100 series Merlins.

The Merlin engine was essential to Britain's war effort, it not only powered the Spitfire, but also the Hurricane, Lancaster and Mosquito. The Spitfires in the Battle of Britain were fitted with the Merlin III of 1,030 horsepower.

Developed as a replacement for the Kestrel engine that had powered the RAF's graceful Fury Biplanes in the `30s, and whose development had been spurred by the American Curtiss engines, it is perhaps surprising that the Merlin was designed at all. When the Merlin was on the drawing board a simple development of the Kestrel called the Peregrine promised to be very successful, and a 24 cylinder variant called the Vulture was hoped to give 1,700 horsepower. There was also the chance that the "R" engine that had powered the Supermarine S6 could be developed as a production engine (the Griffon). Thus the Merlin was seen as something of a stop-gap to fill the void between the Vulture and the Kestrel. It is just as well the Merlin existed, the Vulture engine had a very troubled time in development and two aircraft programs based on it, the Avro Manchester bomber and the Hawker Tornado fighter had to be cancelled. The Peregrine overcame some early problems, but simply did not have the development potential of the Merlin, and the excellent Whirlwind fighter that was powered by a pair of Peregrines was only produced in small quantities. The Griffon only became available in quantity during the last two years of the war. Of course there was another manufacturer of in-line engines in Britain, D. Napier and Sons, but again both of their major engine projects, the Dagger of 1,000 hp and the Sabre of 2,000 hp, had problems. Napier persevered with the Sabre, but it was only during 1942 that they became available in any numbers to power the Hawker Typhoon. Thus it was the Merlin that had to meet all Britain's in-line aero engine needs for the early war years.

The Merlin was at first designed to have a novel cooling system. Evaporative cooling was to be provided by condensers in the wings with a small retractable radiator for use at low speeds and when taxiing. Then Rolls-Royce adopted Ethylene Glycol as a coolant, which is more efficient than water, a radiator for the new coolant could be much smaller than those used with water-cooled engines, the wing condensers were then done-away with. The cooling system was vulnerable to damage by gunfire, particularly as the header tank was situated at the very front of the aircraft. A hit here by the rear gunner of a German bomber would cause a Spitfire pilot to have to break off his attack and land before the engine overheated. Even worse, pure Ethylene Glycol is flammable and added to the risk of the engine catching fire.

Designed by Rolls-Royce as a private-venture, the Merlin was able to take advantage of the new 100 octane fuel developed in the U.S.A. The Merlin only had one disadvantage when compared with German engines, the latter were fitted with fuel injection to deliver a precise charge of petrol to the combustion chamber. The Merlin still used a carburetor, which had the advantage of being much simpler and needing much fewer components, but it did cause the Merlin to "conk-out" if negative G forces were applied. Thus a German pilot with a Spitfire on his tail could simply pull negative G nosing into a dive and the Spitfire would fall behind until the engine picked up, only a matter of a second or two, but that second was all the German needed. Spitfire pilots developed a way around this by doing a half-roll before following into a dive. This meant that the force of gravity acted in the opposite direction and the Merlin was unaffected. In 1941 a carburetor modification, developed by Miss Tilly Shilling, enabled the Merlin to carry on working with short periods of negative G, a vital stop-gap until the introduction of true negative G carburetors in 1943.

Merlin development might have stagnated after 1940, any further increases in power needed a more efficient means of transferring the heat away from the engine. Rolls Royce responded with a mixture of water and Ethylene Glycol which was put under pressure. This mixture also reduced the fire risk associated with using pure Ethylene Glycol. This system was first used in the Merlin XII used in the Spitfire Mk II. The rapid introduction of this system was only made possible by everything Rolls Royce had learnt about pressurized cooling when developing the Goshawk and early Merlin condenser systems.

As piston engines get higher, they lose power because the air gets thinner. What is needed is a fan to suck more air into the engine and improve combustion, just like bellows in a furnace. Such a device is called a supercharger. It was the introduction of a more powerful two-stage supercharger to the Merlin that produced the leap in performance of the Mark VIII and IX Spitfires.

The Merlin was produced under license in America by the Packard company. These engines were used in the Spitfire XVI, but they also found use as the power plant that enabled the P51 Mustang to be transformed from a low altitude army cooperation fighter into the long range, high altitude nemesis of the Luftwaffe.

One thing that is often forgotten is that the capacity of the Merlin was quite small when compared to the opposition. The Merlin had a capacity of 27 litres, whereas the DB601 of the Messerschmitt was 39 litres and the BMW801 engine of the Focke-Wulf 190 had 42 litres. The superiority of the later Merlin engine Spitfires (ie Mk IX) over these Luftwaffe aircraft is all the more remarkable when this is remembered.

The Rolls-Royce Merlin Engine.

Type - Twelve Cylinder 60 Degree Upright V Liquid Cooled Internal Combustion Engine.

Bore x Stroke - 5.4in x 6in (137.3mm x 152.5mm)

Displacement - 1,647 cu in (27 liters)

The Merlin III

Take Off Power: 880 HP AT 3,000 RPM

International Rating: 990 Hp AT 2,600 RPM At 12,250 Ft.

Max Power: 1,440 Hp At 3,000 RPM At 5,500 Fi.

Weight: 1,375 Lbs.

The Merlin 66

Take Off Power: 1,315 Hp Ay 3,000 RPM

Max Power: Over 1,650 Hp.

Weight: 1,650 Lbs.

The Development Lines

Single Stage, single speed supercharger

Merlin I

Merlin II

Merlin 45/46

Single Stage, two speed supercharger

Merlin X

Merlin XX

Two Stage, two speed supercharger

Merlin 61/64

Merlin 66/67/76/85

Merlin 100 series

Merlin 130

Merlin 140

The Rolls - Royce Griffon Engine

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The Rolls-Royce Griffon Engine

The first Griffon was built in 1934, and was effectively a de-rated engine of "R"-type, as was used in the Schneider- Trophy winning Supermarine S6 aircraft. As such it was a V12 liquid-cooled engine of 37 litters swept volume. Much of the design philosophy for the Griffon was to keep the overall dimensions close to those of the Merlins, to allow interchangeability. It is unfortunate that this engine was never developed to the degree that the Merlin was, and never exceeded it in overall power development. The major differences for the pilot was a less-smoothly running engine and one that rotated the propeller the opposite way to the Merlin. The standard anti- torque actions applied at takeoff power also needed to be the opposite way round to prevent a rapid departure off the side of the runway! This resulted from a decision by a committee of The Society of British Aircraft Constructors to aim for a "universal power plant". The rationale was that any aircraft with a power plant of around 2000HP should be able to have virtually any available comparable engine replaced should the original fail. Consequently direction of rotation of the Griffon had to change to match the engines of Bristol, Napier and Armstrong-Siddley (the Merlin, which was in widespread use at that time, especially by the USA- whose aero engines all turned the same way as the Merlin- stayed as it was). The cylinder firing order was changed to produce less resonance in the crankshaft and reduce the risk of failure. By June 1940 the Griffon II was rated at 1720HP with 1495HP at 14 500 feet. The First Griffon-powered production Spitfires were the Mk XII with a 1815HP Griffon VI. All Griffons had a Coffman cartridge starter.

By 1943 the two-speed two stage Griffon 60 series were introduced. The Griffon 65 was rated at 2035HP at 7000 feet, while the Griffon 66 included a blower for cabin pressurization in the Spitfire PRXIX. Griffon 72 and 74 were produced for the Firefly at 2245HP at 9250 feet, while the Griffon 83 to 88 had gear trains for contra-rotating propellers. The ultimate Griffon was the Griffon 101 with a three-speed supercharger which was rather temperamental, but also pushed the Spiteful at 494 MPH, and was never put into production. The last military Griffons flying were the Griffon 58 of the Shackleton, designed to deliver 2455HP at low level with water/methanol injection into the supercharger and 25lb boost, driving contra-rotating propellers. On the retirement of the Shackletons, some of the engines have been converted for driving the Griffon-engine PRXIX of the BBMF. Even more interestingly, an ex-Shackleton Griffon with the contra-rotating prop mechanism retained has been fitted to a PRXIX in the USA.

The Development of The Rolls-Royce Griffin

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The Rolls-Royce Griffon

Development of the Griffon Engine began at Derby, England 1939 when Harry Cantrill was assigned to develop a conventional V-12 scaled up from the 1650 cu-in Rolls-Royce Merlin. The engine was intended to produce more than 1,500 HP at low altitudes for naval torpedo bombers. For maximum utility, it was decided to keep the engine as compact as possible so it could replace the Merlin in some applications. The resulting design had approximately the same frontal area as the Merlin and was actually shorter. The bore and stroke was the same as the Rolls-Royce "R" Schneider Cup race engines of 1929 and 1931, which were direct ancestors to the Griffon, resulting in an displacement of 2,240 cubic inches.. The Merlin proportions of the Griffon were partially achieved by moving the camshaft drives and magneto to the front of the engine.

While the displacement of the Griffon increased by 36% over the Merlin, power did not increase proportionally. This was because the piston speed of both engines is limited to about the same value (3,000 ft/min) reducing the maximum RPM of the Griffon compared to the Merlin, and also because the Griffon's larger cylinder size did not allow as much boost pressure without destructive detonation as the smaller Merlin. The Griffon 57's 2,450 HP is limited by the maximum permissible boost of 25 psig (pounds per square inch gauge, equivalent to 39.7 psi or 81" hg absolute) -vs- 2,270 HP for the V1650-11 Merlin at 29.5 psig. The Griffon turns at 2,750 RPM produces 23 power strokes/sec, and the brake mean effective cylinder pressure (BMEP) is 315 psi -vs- the Merlin's 3,000 RPM producing 25 power strokes/sec with a 360 psi BMEP. Please note that US and British boost specifications use different conventions with respect to absolute or gauge pressure, so we append a g for gauge or an a for absolute to applicable pressure measurements.

The Griffon began with a single-stage supercharger which could run at two different speeds -- the medium-speed (MS) ratio was used at sea-level, and the full-speed (FS) ratio at altitude. As the Griffon evolved two-stage supercharging was introduced, implemented with a clever compact design which combined both impellers in a single partitioned housing -- this was dramatically smaller than the "auxiliary" second stages used for both Merlin and Allison V-1710 engines which consisted were essentially stand-alone units linked by a drive-shaft to the engine. Eventually two-stage three-speed superchargers were used for prototype altitude-rated engines which provided high performance over a wide range of operating altitudes.

The Griffon was initially developed at the request of the British Navy, the Fleet Air Arm or FAA. Navy aircraft tend to be larger and heavier than their land based counterparts, which obviously puts greater demand on the engine if performance is to be maintained. To meet this demand Rolls reverted back to the concept of the Schneider Trophy "R" engine. The Griffon, essentially a modernized Merlin was a 60 degree V-12 with 6.0 inch bores and 6.6-inch stroke giving a 2,239 cubic inch displacement, same parameters as the "R". But this was a totally new engine featuring many design updates. Development started in 1939 and compared with the Merlin development went quite smoothly. Several deviations were made from previous Rolls-Royce V-12 practice. The camshaft and magneto drives were taken from the front offering two advantages. Firstly, the critical timing function of the valves and the ignition would not be left to the mercy of the torsional excursions of the crankshaft. Secondly, the length of the engine was reduced, thus satisfying one of the requirements of the Griffon that it should be capable of retrofitting in existing Merlin powered aircraft. The magneto and camshaft drive gears tapped of the propeller reduction gear for their drive requirements along with the starter. Early development Griffons also drove the supercharger from the front via a long quill shaft which ran under the crankshaft. Due to problems, this promising idea was quickly dropped. Instead, the supercharger took it's drive in a similar way to the Merlin via a quill shaft splined into the rear of the crankshaft. Early engines featured single stage, two speed supercharging again copying Merlin practice but beefed up to take the heavier loads imposed upon it. The crankshaft, also like the Merlin was a 120 degree forged unit supported in seven cross bolted main bearings. However, the firing order was different from the Merlin. A 60 degree V-12 with a 120 crank and paired throws has a number of permutations on ideal firing order, no one being superior to another provided the intake system is "tuned" for the firing order chosen. However, the exhaust note will vary. This gave the Griffon its classic "Griffon Growl" exhaust sound, not as sweet as the Merlin but still impressive!! Different valve timing contributed to the difference in exhaust note. The Griffon had a relatively modest 28 degrees of overlap and 248 degrees of cam duration compared to the Merlin's more radical 43 degrees of overlap and 263 degrees of duration. Later Merlins had 70 degrees of overlap and 288 degrees of duration. A further refinement was made to the propeller reduction gear pinion drive by incorporating a floating ring at the crankshaft end featuring male and female splines. This was an effort to further isolate the pinion gear from the torsional vibration of the crankshaft. After the debacle with the ramp head on the Merlin the Griffon featured the by now ubiquitous and well-proven Kestrel based cylindrical combustion chamber with zero degrees included valve angle. Incorporation of end-to-end crankshaft lubrication was another lesson learned from Merlin experience. Furthermore, this feature proved so successful, all subsequent Rolls-Royce piston engines employed it after it's introduction in the 100 series Merlin. One of the design peculiarities of the Merlin, which dated it to the 1930’s, was the extensive use of external oil lines rather than the more modern internal oil galleries. These external oil lines tended to be maintenance headaches at times being major contributors to oil leaks and the occasional fracture resulting in serious engine damage. By comparison the Griffon was a clean design with few external oil lines. Accessories required for aircraft systems such as electric generators, hydraulic pumps, vacuum pumps etc., took their drive from a remotely mounted gearbox driven from a power take off tapped off the wheel case. The Merlin on the other hand had accessories cluttering the exterior of the engine with the vacuum pump and propeller governor mounted on the front, the tachometer generator or tachometer drive, air compressor, and hydraulic pump were mounted on the cylinder heads driven off the camshafts. The lower crankcase also offered a drive take off for a hydraulic pump, overall a somewhat disorganized arrangement. Interestingly, the Griffon rotated in the opposite direction to a Merlin. No advantages exist for either direction of rotation.

Shoehorning the Griffon into a relatively light single engine aircraft such as the Spitfire created some handling difficulties primarily due to the enormous torque reaction which could amount to a very significant 4,700 pounds feet at take-off power. Designing a gear reduction unit for a contra rotating propeller turned out to the definitive answer after various aerodynamic attempts such as enlarged vertical stabilizer area only presented partial solutions. The 80 series were the first Griffons to receive dual rotating propeller drives and were introduced just prior to the end of World War II. This was accomplished by having two pinions and two reduction gears. The front pinion was of a smaller diameter than the rear and drove an additional idler gear resulting in opposite rotation for the propeller reduction gear. The reduction gears drove co-axial, contra rotating propeller shafts. Contra rotating props were essential for the Navy version of the Griffon Spitfire, known as the Seafire due to the extremely hazardous nature of carrier landings particularly during a go-around when maximum power needed to be applied at low altitude and low air speed. Torque reaction pulled a Griffon Spitfire with a single prop to the right, towards the carrier island, obviously a very s situation. Other internal features of the engine followed Merlin practice.

Early Griffons entered service with two speed, single stage superchargers rated at 1,735 hp at 16,000 feet which soon gave way to two speed, two stage superchargers with inter-cooling and after-cooling, again similar to Merlin practice, rated at 2,350 horsepower which was achieved with the extremely high manifold pressure of 25 psi or 80 inches of mercury.

The two speed supercharger shifting was automatic, relying on atmospheric pressure via an aneroid switch to shift to the appropriate blower speed. Centrifugal bob weights mounted on the blower clutches add to the drive capability of the clutches, i.e., the faster it spins, the harder the clutch grabs. When the blower shifts, a small degree of clutch slip is built in; otherwise the accelerating forces would damage and possibly strip the blower drive gears. The clutches also absorb some of the torsional vibration emanating from the crankshaft, this design feature may help explain why no Rolls-Royce piston engines except for the Eagle 22 last of the piston engine developments required no dynamic crankshaft counter weights.

A few examples of the 100 series Griffon were built with three speed, two stage supercharging, the only application being the Supermarine Spiteful, a development of the Spitfire featuring laminar flow wings. The two stage two speed Griffons, the "60" series, were typically rated at 2,375 hp at 1,250 feet in low blower of "M.S." (moderate speed) and 2,130 hp at 15,500 feet in "F.S." (full speed). All horsepower ratings were at 2,750 rpm. Carburetion could be via a three-barrel injection carburettor built by Rolls-Royce based on the Bendix injection unit. Alternatively, a single Point Rolls-Royce injection unit based on the speed density principle pioneered in the United States accomplished carburetion. Like the Bendix unit, atomized fuel was sprayed into the eye of the first stage impeller.

Fairey Firefly

The Fairy Firefly, a carrier based Fleet Air Arm torpedo bomber was the first recipient of the Griffon. Initially fitted with single stage two speed Griffon II's, later Firefly's were upgraded with two stage, two speed engines. One of the first missions flown by Fireflys was the attack in November 1944 on the Tirpitz

No new ground was broken in the design of the Firefly, being a low wing stressed skin design featuring manual wing folding. Early Fireflys used a “chin” type radiator mounted under the engine. With the introduction of the two stage powered aircraft, the radiators and oil coolers were relocated to the wing leading edge

The Griffon Spitfire

In early 1941, the Focke Wulfe 190 menace appeared over England for the first time. It created havoc with it's superior performance over anything the British could throw against it at the time. Immediately plans were put in place to shoe horn the Griffon into the Spitfire - this was not an easy task. The finished product was a masterpiece of engineering incorporating the state of the art technology for engine installation at that time. From the firewall forward everything was new. The oil tank was relocated from it's previous position under the engine to the firewall. A fabricated sheet aluminium mount, similar in concept to the P-51, replaced the previous chrome molly tabular mount. Three bumps at the front of the cowl accommodated the valve covers and the single large magneto. Due to the much greater heat rejection requirements of the Griffon, the familiar under wing radiators now grew, having far greater depth for additional radiator capacity. Spitfire XII's were the first recipient of the Griffon powered by the Mk. III or IV variants with single stage, two speed supercharging. A number of subsequent Spitfires retained Merlin power but towards the end of Spitfire production all were powered by Griffons. Starting with the Spitfire XIV, two-stage, two-speed inter-cooled, after-cooled superchargers became standard, all of which were 60 series engines.

The Supermarine Spitfir and Seafang

Designed to Air Ministry Specification F.1/43 and Navy specification N.5/45 as the Seafang. Under development throughout most of World War II the final and ultimate Spitfire variation, the Spiteful along with the Navy derivative, the Seafang, did not see action during World War II. Essentially a brand new design with a lot of Spitfire influence, it was the first Supermarine aircraft to feature lamina flow flying surfaces. Other design refinements included less drag producing, wide slim radiators mounted under the wings and wide track, inwardly retracting landing gear, correcting one of the Spitfires few faults, that of poor ground handling. First flown June 30th. 1944 the new design looked promising although shortly afterwards the prototype was destroyed in an accident, killing the test pilot. This set the program back and finally the Spiteful/Seafang faded away into history with only a small handful of aircraft being built which did not enter squadron service. Initially powered by a Griffon 65, later versions had this engine replaced by a Griffon 85, essentially the same engine but driving a six bladed contra rotating propeller. An interesting footnote is the fact that Spiteful flying surfaces were used as the basis for Supermarines first jet powered aircraft, the Attacker.

Rolls-Royce Griffon

Although the Griffon entered service long after the Merlin, in many ways it is an older design, being based on the Buzzard which first ran in 1928 and which itself was a scaled up version of the Kestrel. The big Buzzard ran at only 2,000 rpm and was mostly used to power flying boats, but was developed into the "R" engine that ran at 3,400rpm for short periods. The "R" powered the Supermarine S6 to it's Schneider wins in 1929 and 31. A de-rated version of the "R" was being developed in 1933 but this was dropped so that Rolls Royce could concentrate on the Merlin. It is perhaps surprising that work on the Griffon did not start again in earnest until 1939, 10 years after the "R" engine flew. However, once restarted, work on the Griffon proceeded at a fantastic rate and the new engine was put to good use in the Spitfire. The Griffon ran at 2,750 rpm, a remarkably high speed for such a big engine.

The first Griffons had single-stage superchargers, and were fitted to the Spitfire MK XII. These aircraft arrived just in time to take on the Focke-Wulf 190 "Tip and Run" fighter bombers that were attacking England's South Coast. Their impressive low-level performance was used to good effect.

For high altitude a two-stage supercharger was needed and these arrived in the Spitfire XIV and XVIII. This enabled the Spitfire to stay in the forefront of fighter performance until the end of the war.

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The Rolls-Royce Merlin and Griffon Engines

Single Stage, single speed supercharger

Single Stage, two speed supercharger

Two Stage, two speed supercharger

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The Rolls-Royce Merlin	The Rolls-Royce Griffon

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Spitfire Mk IX, with the markings of Wing Commander Douglas Bader	A Spitfire Mk II from No 65 Sqdn, seen here at Kirton-in-Lindsey in 1941.