The Development of the Rolls-Royce Griffon

Graham White

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 its 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 wheelcase. 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 engined 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 intercooling and aftercooling, 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. Carburation 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 carburation. 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.

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 moly 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 intercooled, aftercooled superchargers became standard, all of which were 60 series engines.

Supermarine Spiteful 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.

Martin Baker M.B.5

Another near miss was the Martin Baker (of ejector seat fame) M.B.5 single engined fighter. The MB5 was superficially similar to the P-51, but considerably larger and featuring different construction methods. A chrome moly tube fuselage covered with quickly detachable metal panels and a classic D spar wing with a laminated steel spar, a design feature of Martin Baker aircraft. Built only in prototype form, this promising project was cancelled

Paper Airplanes

If a little is good then more must be better right? This was the philosophy behind a scheme to install the Griffon into the P-51. Unlike the Griffon conversion of the Spitfire, the Griffon P-51 entailed a totally new design incorporating only the flying surfaces. An all-new fuselage featuring a mid engined layout with the pilot sitting in front of the engine driving a six bladed Rotol contra rotating prop would have made it new aircraft. Drive to the propeller was via transfer gears mounted at the front of the engine. The drive shaft ran under the cockpit terminating at the propeller reduction gears mounted in the nose. A torque tube mounted on the propeller reduction gear case at the front and on the engine at the rear enclosed the drive shaft thus alleviating the nose structure of the aircraft from the considerable torque reaction loads, which were instead transmitted back to the engine. Splines on both ends of the torque tube allowed for longitudinal float. Three early Allison powered Mustang I's, equivalent to Mustang A's were obtained to supply parts for the project. Substantial work had been completed when the project was cancelled for the usual reasons during this time frame, gas turbine development

The Red Baron RB-51

Complying with the hot rodders premise, there ain't no replacement for displacement, the Red Baron racing team produced a race plane that, unfortunately never reached it's true potential.

Based on a successful racing P-51D Mustang, Ed Browning, owner of the Red Baron Racing team purchased the aircraft in 1973. At this stage considerable airframe modifications had already been performed including clipping the wings and a highly modified cockpit canopy. Still retaining the Merlin for power, Browning campaigned the aircraft through 1974. At the end of racing for the year, Browning enlisted the help of Pete Law and Bruce Boland, two Lockheed engineers familiar with the unlimited racing scene, to modify the aircraft for Griffon power. A stockpile of former RAF Griffon 58's from Shackletons were purchased along with De Havilland/Rotol six bladed contra rotating propellers. Boland and Law totally redesigned the P-51 from the firewall forward incorporating new engine mounts cowling etc. Due to the additional length of the Griffon compared to the V-1650-9, the firewall was moved aft by 9 inches. This also helped preserve the correct centre of gravity without resorting to additional weight. Although the standard P-51 radiator ducting was retained, incorporating front to rear flow instead of the standard cross flow modified the radiator. Even with the improved radiator, heat rejection would have been inadequate therefore spray bars were incorporated. At high engine temperatures, water was sprayed onto the radiator, intercooler/aftercooler and oil cooler cores. This explains the steam trail issuing from most race planes. Starting out with a basic Griffon 58 from a Shackleton, Randy Scoville, the brilliant engine builder who built the Red Baron engines used a Griffon 64 crankshaft because of the additional counter weights on this unit, and Griffon 57 connecting rod and piston assemblies. It was felt that two stage supercharging would be essential. Consequently, a Griffon 64 blower was grafted onto the -58 crankcase. Severe space restraints would not allow the use of the -64 carburettor, therefore the intake elbow from a Mk. XIX Spitfire was modified and turned 180 degrees resulting in down draught induction. A Bendix PR-58 carburettor from a C series Pratt and Whitney R-2800 was mounted on top of the modified intake elbow. Thanks to experience working with this carburettor, it was not difficult to reflow the PR-58 for Griffon requirements. A large airscoop on top of the cowling supplied induction air. The camshafts were modified by grinding the base circle thus yielding additional lift although interestingly the timing was left stock. The profile was modified to allow a gentler lift off the seat and a similarly gentler closing for both intake and exhaust valves. Fuel was 115/145 PN with water/methanol ADI (anti detonation injection). ADI was injected at the rate of 1/2 pound for each pound of fuel burned.

Propeller modifications included removing 6 inches from the tip of each blade, re-twisting the blades and modified governor springs and bob weights for increased rpm. Test flying brought to the surface handling problems which were not satisfactorily resolved for several years. Worst among them was a serious dutch roll tendency at high speed. Resolution of this characteristic required the manufacture of a totally new vertical stabilizer. As can be expected engine problems also abounded including the failure of connecting rods, one being due to a faulty rod bolt. More seriously, persistent failure of the blower gears plagued the team. The gears were custom made units that could not stand the loads being imposed upon them; power requirements for the supercharger would be in excess of 400 horsepower. Loss of the blower drive would still allow the engine to run naturally aspirated and produce enough power to effect a safe landing.

By 1979 the aircraft was sufficiently well developed to make an attempt on the world's air speed record for piston driven aircraft. In August the aircraft was flown to Tonapah, Nevada but the hoped for 100 degree temperatures never materialized. The early attempts were frustrated by numerous problems including a failed connecting rod and turbulence. On August 14, 1979 conditions were far from ideal but as good as they were going to get in the foreseeable future. Steve Hinton, the well known, brilliant race pilot took the Red Baron out with an air temperature of 68 degrees and broke the existing record with an average 499.018 mph, frustratingly close to exceeding 500. With further engine development and ideal conditions, the RB-51 could have exceeded 525 mph.

110 inches manifold pressure at a modest 2,850 rpm was used for the record attempts. The engine was potentially capable of 3,900 horsepower. Steve Hinton related to me that each additional 50 rpm yielded another 5 inches of manifold pressure. Coolant temperature was held to 100 degrees C and oil was kept at 80 degrees C.

With the record in hand the aircraft was prepared for Reno, '79. During the final Gold Race with Steve Hinton in second place the old nemesis of blower gear failure occurred. This time however things went from bad to worse to catastrophic. Broken pieces of gear jammed the pressure oil pump resulting in rapid engine failure due to a failed rod. Steve could not get the prop feathered resulting in the contra prop acting as a massive air brake. The ensuing crash landing in the desert resulted in a huge fireball and total destruction of the aircraft but miraculously, Steve came out of it alive albeit seriously injured. Thus the final chapter was written on an aircraft that never saw it's true potential realized.

Special thanks to: Steve Hinton and Randy Scoville for their assistance on the Red Baron piece

From The Web

I thoroughly enjoyed the Avro Shackleton website, but may I correct a minor error in the history of the plane? The Rolls-Royce Griffon was not, as is popularly assumed, a development of the Merlin, but rather is a direct descendant of both the Buzzard (1925-33) and the R-Type racing powerplant (1929-31).

While the Griffon benefited from technical developments rightfully attributed to the Merlin, the Griffon was of considerably different block architecture (thanks to the Buzzard and R-type DNA) and rotated in the opposite direction to the Merlin. Additionally, bore and stroke were also identical to that of the Buzzard and the R-type. The first Griffon to be built and test-run on an engine stand was, in fact, a de-rated R-type. Mind you, this was in 1933.

Hawker and Supermarine work with the PV-12 (later Merlin) placed more need to develop that engine for the upcoming generation of new monoplane fighters for the RAF (thank God), so Griffon development was placed on the back burner till about 1939 when the engine was reengineered (heavily) as the Griffon II.

I'll be the first person to point out that I'm being pretty pedantic about all this, but being a long time Shack fan, I figured the pages - and the plane - deserved getting things straighter. If only incrementally.

Bob Hall Rose Bay, NSW



Neil Cairns.

Back in the early 1940's, one very clever engineer was busy developing a very large version of the famous Vee 12 series of four stroke, petrol, piston engines, that Rolls Royce had become world renowned for. In 1940 A.A. Rubbra had become the Rolls Royce Chief Designer, after joining them in 1925 as an assistant engine tester. Arthur Rubbra, in true RR tradition, used well-tried engineering and the best materials to produce the early versions of the Griffon aeroengine. Today, this is almost sixty years ago, and to many just a bit of distant history, to those born since the late 1950's, it seems of no consequence at all.

The actual ancestral line of the Griffon engine runs even further back, to a derated,'' ( detuned,) version of a very famous RR engine indeed. The first experimental Griffon was about in 1933 and up and running, and was a close relative of the 'R' engine used in the Schneider Cup air races of 1929 and 1930. There was a whole series of Vee 12 RR engines about at this time, and the Griffon version was actually shelved in 1933 to be left in case it was needed in later years. That is exactly what happend, because by 1939 the drawings had been dusted off, and the Griffon Mk 1 ran on the test bed as an experimental engine. By 1942 the Griffon was in production, using the original bore and stroke of the racing 'R' engine, being termed a Griffon Mk 2. It was fitted to the Firefly fighter, and drove a single propeller.

The years passed by and the Griffon went through much development and updating, gaining a two-speed supercharger and a contra-rotating propeller for Spitfire and Spiteful use in the Naval carrier role. Fuel injection into the eye of the supercharger came along during the war, and improved the performance. The development followed that of the smaller Merlin Vee 12 aeroengine though behind it; though the Griffon had improvements like end-feed oil lubrication for the crankshaft first. By the time the Griffon found its way into the Shackleton four engined maritime reconnaissance aircraft it was well up the 'mark' range, Mk 54 onto Mk. 54A in fact.

So after WW2 by the time the Shackleton was flying with its four Griffons, the engines had been about a long time. In terms of power and performance the contra-rotating propellers were need to absorb all that power, and to keep the prop-disc a reasonable size. Years rolled past, and the Shackleton with its ancient engines became folklore, remaining in use an unprecedented number of years, well past its sell-by date in modern terms. The men and women who serviced and flew it once drove Austin Seven side-valve motor cars, then onto overhead-valve Morris 1000's and Mini's, and ohv Ford Cortina's, onto VW Golfs, then onto Vauxhall/Opel Astra's, to today's super quiet super-mini's with multi-valve heads, fuel injection, turbos, etc.

But wait a minute, the Griffon engine had four valves per cylinder all those years ago, and it had fuel injection, and a supercharger, (a turbo is only an exhaust powered supercharger after all.) Do today's modern car drivers ever consider that their engine shares so much with the Griffon, in that both have cast aluminium heads/blocks/sumps, four valves per cylinder, fuel injection, nimonic exhaust valve seats and valve head, exhaust valve stems filled with sodium to aid cooling, stellited valve tips to reduce wear, the twin overhead camshafts, engine sections held together with long through bolts, an engine management system, (though the Griffons was mechanical not solid-state,) sealed cooling systems with special anti-corrosive/anti-freeze coolant mixture, anti-interference ignition leads; infact there is only the extra cylinders, the propeller and magneto missing!

I wonder if they (you,) do. There is nothing new under the Sun; someone will have tried it sometime, somewhere, somehow. It took your1990's car over 50 years to catch up with the Griffon, first seen in 1933!