| Rolls-Royce Griffon | |
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| Preserved Rolls-Royce Griffon with cutaway sections. | |
| Type | Piston V-12 aero engine |
| Manufacturer | Rolls-Royce |
| First run | November 1939 |
| Major applications | Supermarine Spitfire Avro Shackleton |
| Number built | 8,108 |
The Rolls-Royce Griffon is a British 37-litre (2,240 cu in) capacity, 60-degree V-12, liquid-cooled aero engine having a similar general configuration to its smaller capacity stablemate, the Merlin. Design work on the Griffon started in 1933, but development was temporarily put on hold to concentrate efforts on the smaller Merlin and the engine did not go into production until the early 1940s.
The Griffon was the last in the line of V12 aero engines to be produced by Rolls-Royce Limited with production ceasing in 1955.[1] Griffon engines remain in Royal Air Force service today with the Battle of Britain Memorial Flight and also power the last remaining airworthy Avro Shackleton.
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Design and development
Design work on the Griffon was started in 1933.[2] The design process was relatively smooth compared with that of the earlier Merlin and an experimental engine, a derated version of the 'R', was up and running shortly after. The new design was originally intended to be interchangeable with the Merlin, and to be used as a low-altitude engine for naval aircraft such as the Fairey Firefly, but a formal suggestion to fit a Griffon in a Spitfire was made by Supermarine's chief design engineer Joe Smith in 1940.[3] However, 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 (1,649 cu in) Merlin which had already surpassed the output achieved with the early Griffon.
Compared with earlier Rolls-Royce designs, the Griffon engine incorporated several advances which meant it would be physically only slightly larger than the Merlin, in spite of its larger capacity of 37 L (2,240 cu in). For example, the camshaft and magneto drives were incorporated into the propeller reduction gears at the front of the engine rather than being driven directly from the back of the crankshaft. This allowed the overall length of the engine to be reduced, as well as making it more reliable and efficient. Earlier engines, including the Merlin, had large numbers of external oil lines. In service these caused continual problems, being prone to leakage[4] and fractures, which could drain the engine in seconds. They were also vulnerable to battle damage. The Griffon engine incorporated extensive oil galleries which were cast into the cylinder block and cylinder heads; although commonplace in modern engine design this was a big step forward in the late-1930s. The internal oil flow was not only more efficient in terms of lubrication, it also required less maintenance.
An assumption prevailed that the production Griffon was derived from the Rolls-Royce R racing engine used in the Schneider Trophy races. However, apart from some commonality in bore and stroke, the only component of the Griffon which had any direct links was the crankshaft.[5]
When the development work on the Griffon was resumed, it was decided to fit the engine to a Spitfire. The first example of this was a single Spitfire Mk.IV (DP845) a modified clipped-wing Mk.III which flew with a Griffon IIB on 27 November 1941 with Jeffrey Quill at the controls.[6]
Basic component overview (Griffon 65)
From "Jane's":[7]
- Cylinders
- Twelve cylinders consisting of high-carbon steel liners set in two, two-piece cylinder blocks of cast aluminium alloy having separate heads and skirts. Cylinder blocks mounted with an included 60-degree angle onto inclined upper faces of a two-piece crankcase. Cylinder heads fitted with cast-iron inlet valve guides, phosphor bronze exhaust valve guides, and renewable "Silchrome" steel-alloy valve seats. Two diametrically opposed spark plugs protrude into each combustion chamber.
- Pistons
- Machined from "R.R.59" alloy forgings. Fully-floating gudgeon pins of hardened nickel-chrome steel. Two compression and one drilled oil-control ring above the gudgeon pin, and another drilled oil-control ring below.
- Connecting rods
- H-section machined nickel-steel forgings, each pair consisting of a plain and a forked rod. The forked rod carries a nickel-steel bearing block which accommodates steel-backed lead-bronze-alloy bearing shells. The "small-end" of each rod houses a floating phosphor bronze bush.
- Crankshaft
- One-piece, machined from a nitrogen-hardened nickel-chrome molybdenum steel forging. Statically and dynamically balanced. Seven main bearings and six throws. Clockwise rotation when viewed from rear.
- Crankcase
- Two aluminium-alloy castings joined together on the horizontal centreline. The upper portion bears the wheelcase, cylinder blocks and part of the housing for the airscrew reduction gear; and carries the crankshaft main bearings (split mild-steel shells lined with lead–bronze alloy). The lower half forms an oil sump and carries the main pressure oil pump, supercharger change-speed operating pump and two scavenge pumps. It also houses the main coolant pump which is driven through the same gear-train as the oil pumps.
- Wheelcase
- Aluminium-alloy casting fitted to rear of crankcase. Carries the supercharger; and houses drives to the supercharger, auxiliary gearbox coupling, engine speed indicator, airscrew constant-speed unit, intercooler pump and fuel pump, as well as the oil and coolant pumps in the lower half crankcase.
- Valve gear
- Two inlet and two exhaust poppet valves of "K.E.965" steel per cylinder. Exhaust valves have sodium-cooled stems. "BrightRay" (nickel-chromium) protective coating to the whole of the combustion face and seat of the exhaust valves, and to the seat only of the inlet valves. Each valve is held closed by a pair of concentric coil springs. A single, seven-bearing camshaft, located centrally on the top of each cylinder head operates 24 individual steel rockers; 12 pivoting from a rocker shaft on the inner, intake side of the block to actuate the exhaust valves, the others pivoting from a shaft on the exhaust side of the block to actuate the inlet valves.
Engine capacity and mass flow
Although it is common practice to compare different piston engines and their performance potential by referring to the engine displacement or swept volume this does not give an accurate reading of an engine's capabilities. According to A C Lovesey, who was in charge of the Griffon's development:
The impression still prevails that the static capacity known as the swept volume is the basis of comparison of the possible power output for different types of engine, but this is not the case because the output of the engine depends solely on the mass of air it can be made to consume efficiently, and in this respect the supercharger plays the most important role.[8]
Rolls-Royce applied the advances in supercharging used on the Merlin to the Griffon, and later Griffon versions featured two-stage supercharging and finally a two-stage, three-speed supercharger. This, the Griffon 101, was fitted to the two Supermarine Spiteful XVIs (re-engined production Mk.XIVs) with one of these aircraft, RB518, achieving a maximum speed of 494 mph (795 km/h) with full military equipment.
Pilot conversion
Pilot conversion from Merlin- to Griffon-engined Spitfires was not without teething troubles, the most common problem being the ingrained habit of applying a starboard trim to the aircraft's rudder to offset the tremendous torque produced at takeoff power. As the Griffon's crankshaft rotated in the opposite direction to the Merlin [9] (a legacy of its intended use for naval aircraft, where it is desirable for aircraft to swing to port, away from the superstructure), a starboard bias increased, instead of compensating for, the undesirable effects of torque. This problem was never fully overcome in land-based Spitfires, although the Seafire FR.47 and the occasional Spitfire 21 or 24 were fitted with contra-rotating propellers as standard, thus negating airscrew torque.[10] The Griffon was used in the Avro Shackleton maritime patrol aircraft, also employing contra-rotating propellers.
Variants
The Griffon was produced in approximately 50 different variants, the Griffon 130 being the last in the series. Details of representative variants are listed below:
- Griffon II
- 1,730 hp (1,290 kW) at 750 ft (230 m) and 1,490 hp (1,110 kW) at 14,000 ft (4,270 m); used on Firefly Mk.I fighter
- Griffon VI
- Increased maximum boost pressure, 1,850 hp (1,380 kW) at 2,000 ft (610 m); used on Seafire Mk.XV and Mk.XVII
- Griffon 57
- 1,960 hp (1,460 kW); used on Avro Shackleton
- Griffon 61
- Introduced a two-speed two-stage supercharger with aftercooler similar to that on Merlin 61; 2,035 hp (1,520 kW) at 7,000 ft (2,135 m) and 1,820 hp (1,360 kW) at 21,000 ft (6,400 m); used on Spitfire Mk.21
- Griffon 65
- Similar to Griffon 61 with different propeller reduction gear; used on Spitfire Mk.XIV
- Griffon 72
- Increased maximum boost pressure to take advantage of 150-grade fuel; 2,245 hp (1,675 kW) at 9,250 feet (2,820 m)
- Griffon 74
- Fuel-injected version of Griffon 72; used on Firefly Mk.IV
- Griffon 83
- Modified to drive contra-rotating propellers; 2,340 hp (1,745 kW) at 750 ft (230 m) and 2,100 hp (1,565 kW) at 12,250 ft (3,740 m)
- Griffon 85
- 2,375 hp (1,770 kW); used on Spiteful Mk.XIV
- Griffon 89
- 2,350 hp (1,755 kW); used on Spiteful Mk.XV
- Griffon 101
- 2,420 hp (1,805 kW); used on Spiteful Mk.XVI
Applications
Note:[11]
Survivors
The Griffon engine continues to be used in restored later mark Spitfires worldwide. The Royal Air Force Battle of Britain Memorial Flight is a notable current operator of the Griffon.
The sole remaining airworthy Avro Shackleton is based at the South African Air Force Museum.[13]
Engines on display
Preserved Griffon engines are on public display at the:
Specifications (Griffon 65)
Data from Lumsden[14]
General characteristics
- Type: 12-cylinder supercharged liquid-cooled 60° Vee aircraft piston engine
- Bore: 6 in (152.5 mm)
- Stroke: 6.6 in (167.6 mm)
- Displacement: 2,240 in³ (36.7 L)
- Length: 81 in (2057 mm)
- Width: 30.3 in (770 mm)
- Height: 46 in (1168 mm)
- Dry weight: 1,980 lb (900 kg)
Components
- Valvetrain: Two intake and two exhaust valves per cylinder with sodium-cooled exhaust valve stems, actuated via an overhead camshaft.
- Supercharger: Two-speed, two-stage centrifugal type supercharger, boost pressure automatically linked to the throttle, water-air aftercooler installed between the second stage and the engine
- Fuel system: Triple-choke updraught carburettor with automatic mixture control
- Oil system: Dry sump with one pressure pump and two scavenge pumps
- Cooling system: 70% water and 30% ethylene glycol coolant mixture, pressurised
Performance
- Power output:
- 2,035 hp (1,520 kW) at 7,000 ft (2,135 m)
- 1,820 hp (1,360 kW) at 21,000 ft (6,400 m)
- Specific power: 0.91 hp/in³ (41.4 kW/L)
- Compression ratio: 6:1
- Power-to-weight ratio: 1.03 hp/lb (1.69 kW/kg)
See also
Comparable engines
Related lists
Media
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References
Notes
- ^ Lumsden 2003, p.218.
- ^ Rubbra 1990, p.118.
- ^ Smith had taken over as Chief Designer at Supermarine after R. J. Mitchell's death in June 1937.
- ^ The Merlin, especially early versions which used 100% glycol cooling system, was notorious for losing oil. Photographs of the undersides of Spitfires in flight often show a large amount of oil streaking from the engine cowlings to aft of the wing.
- ^ Flightglobal archive - Rolls-Royce Griffon 65 pdf file Retrieved: 5 February 2008
- ^ Price 1986, p.187.
- ^ Bridgman 1989, pp. 279–280.
- ^ Lovesey 1946, p. 218.
- ^ Lumsden 2003, p.217. The Griffon was a "left-hand tractor" engine, i.e. the propeller rotated to the left when viewed from behind.
- ^ Gunston 1989, p.143.
- ^ Generic types given only, the Griffon was not the main powerplant for some of these aircraft
- ^ (Beaufighter II, Griffon IIB) Lumsden 2003, p.217.
- ^ SAAF 1722 - Avro Shackleton Retrieved: 29 July 2009
- ^ Lumsden 2003, pp.216-219.
Bibliography
- Bridgman, L, (ed.) (1989) Jane's fighting aircraft of World War II. Crescent. ISBN 0-517-67964-7
- Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
- Lovesey, Cyril. "Development of the Rolls-Royce Merlin from 1939 to 1945". Aircraft Engineering magazine. London: July 1946
- Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.
- Price, Alfred. The Spitfire Story: Second edition. London: Arms and Armour Press Ltd., 1986. ISBN 0-85368-861-3.
- Rubbra, A.A. Rolls-Royce Piston Aero Engines - a designer remembers: Historical Series no 16 :Rolls Royce Heritage Trust, 1990. ISBN 1-87292-200-7
Further reading
- Quill, J. (1983) Spitfire - A Test Pilot’s Story. Arrow Books. ISBN 0-09-937020-4
External links
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