Rolls-Royce Griffon
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The Rolls-Royce Griffon was a 2,239.33 in³ (36,696.00 cc), 6.0" bore x 6.6" stroke 60-degree V-12 aero-engine. The usual assumption still prevails that the 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.[1]
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[edit] Development
Design work on the Griffon was started in 1939 and the design process was relatively smooth compared with that of the earlier Merlin. The new design was originally intended 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[2] in 1940. 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 1,649 in³ (27 litre) 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 2,239 in³ (36 litre). 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 being 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[3] and to 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.
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 RG 2SM on 27 November 1941.
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 (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 a contra-rotating propeller as standard, thus negating airscrew torque.
[edit] 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. A. C Lovesey a Rolls-Royce engineer who was a central figure in the development of the Merlin and Griffon said in 1946:
Coming now to specific development items we can, for convenience, divide them into three general classes:
- (a) Improvement of the supercharger.
- (b) Improved fuels.
- (c) Development of mechanical features to take care of the improvements afforded by (a) and (b).
Dealing with (a) it can be said that the supercharger determines the capacity, or in other words the output, of the engine. 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. This applies equally to any engine but the engine has to be capable of dealing with the greater mass flows with respect to cooling, freedom from detonation and capable of withstanding high gas and inertia loads...During the course of research and development on superchargers it became apparent to us that any further increase in the altitude performance of the Merlin engine necessitated the employment of a two-stage supercharger.[4]
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.
The Griffon was also used in the Avro Shackleton maritime patrol aircraft, also with contra-rotating propellers.
[edit] Variants
Note: The Griffon was a "left-hand tractor" engine, i.e. the propeller rotated to the left when viewed from behind.
- 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
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[edit] Specifications (Griffon 65)
General characteristics
- Type: 12-cylinder supercharged liquid-cooled 60° Vee aircraft piston engine
- Bore: 6 in (152.4 mm)
- Stroke: 6.6 in (167.6 mm)
- Displacement: 2,239 in³ (36.7 L)
- 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 updraft carburetor 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, pressurized
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)
- Power-to-weight ratio: 1.03 hp/lb (1.69 kW/kg)
[edit] References
[edit] Notes
- ^ Rolls-Royce Griffon 65 pdf file Retrieved 5 February 2008
- ^ 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 showed a large amount of oil streaking from the engine cowlings to aft of the wing.
- ^ Lecture by Rolls-Royce Engineer A. C Lovesey, 1946.Retrieved: 21 May 2008
[edit] Bibliography
- Bridgman, L, (ed.) (1998) Jane's fighting aircraft of World War II. Crescent. ISBN 0-517-67964-7
- Quill, J. (1983) Spitfire - A Test Pilot’s Story. Arrow Books. ISBN 0-09-937020-4
- 1 Spitfire society
[edit] External links
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