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| V-1650 Merlin | |
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| Packard V-1650-7 Merlin | |
| Type | Liquid-cooled V-12 piston engine |
| National origin | United States |
| Manufacturer | Packard |
| First run | August 1941 |
| Major applications | P-51 Mustang P-40F/L Kittyhawk |
| Number built | 55,523 |
| Developed from | Rolls-Royce Merlin |
The Packard V-1650 was a liquid cooled 27 litre (1649 in3) 60° V12 piston aircraft engine variant of the Rolls-Royce Merlin produced under licence (in the United States) by the Packard Motor Car Company.[1]
Contents |
Design and development
In June 1940, Henry Ford had offered to manufacture 1,000 aircraft a day if the Government would let him do it his way, and during a discussion with Secretary of the Treasury Henry Morgenthau Jr. regarding what the Ford company might produce, Ford's son Edsel tentatively agreed to make 6,000 Rolls-Royce liquid-cooled engines for Great Britain and 3,000 for the U.S.[2] However, at the beginning of July Henry Ford stated that he would manufacture only for Defense, not for Britain, and the entire deal was declared off. Members of the Defense Advisory Commission subsequently began negotiations with other manufacturers in an effort to place the $130,000,000 Rolls-Royce order,[2] and Packard Motor Car Company was eventually chosen because the parent British company was impressed by its attention to high-quality engineering. Agreement was reached in September 1940, and the first Packard-built engine, designated V-1650-1, ran in August 1941.[3]
The first American version of the Merlin was the Packard Merlin 28 (Mark XX). This engine used a single stage, two speed supercharger. As the Merlin 28, it was used for the Avro Lancaster bomber. The USAAF version of this engine was used in the P-40Fs. The initial Packard modifications were done on this engine by changing the main bearings from a copper lead alloy to a silver lead combination and featured indium plating. This had been developed by General Motors' Pontiac Division to prevent corrosion which was possible with lubricating oils that were used at that time. The bearing coating also improved break-in and load-carrying ability of the surface. British engineering staff assigned to Packard were astonished[citation needed] at the suggestion but after tear-down inspections on rigidly tested engines were convinced the new design offered a decided improvement.
The real improvement Packard incorporated into the Merlin was adopting the Wright supercharger drive quill. This modification was designated the V-1650-3 and became known as the "high altitude" Merlin destined for the P-51. The two speed, two stage supercharger section of the -3 featured two separate impellers on the same shaft which were normally driven through a gear train at a ratio of 6.391:1. A hydraulic gear change arrangement of oil operated clutches could be engaged by an electric solenoid to increase this ratio to 8.095:1 in high speed blower position. The high speed gear ratio of the impellers was not as great as the ratio used in the Allison but speed of the impeller alone was not the factor that increased the engine performance at altitude.[clarification needed] The double staging of the compressed fuel/air mixture provided the boost pressure through a diffuser to the intake manifolds which increased the critical altitude of the power plant.
The ability of the supercharger to maintain a sea level atmosphere in the induction system to the cylinders allowed the Packard Merlin to develop 1,210 horsepower (900 kW) at 25,800 feet (7,900 m). The two stage impeller created extreme heating of the fuel/air mixture during the compression process and in order to prevent detonation of the compressed charge, it was necessary to cool the mixture prior to entry into the cylinders. This cooling was accomplished by the casting of an intercooler passage into the wheelcase housing between the first and second stage impellers.
Ethylene glycol coolant was circulated by a pump through this passage to carry off the excess heat generated by the impellers. Without the intercooler the temperature of the charge could be as high as 400 °F (204 °C). The intercooler in itself was not adequate to deal with the high temperature and an additional cooling fin and tube core was placed between the outlet of the blower and the induction manifold to the cylinders. This radiator was known as an aftercooler and served as a reservoir for the system.[clarification needed] The glycol mixture used for the supercharger cooling was independent of the main engine cooling system and used a centrifugal pump driven by the engine to circulate the coolant through an aircraft radiator system at a rate of 30 gallons[clarification needed] per minute.
This combined system reduced the charge temperature to suitable levels. The throttle valves in the updraft carburettor throat were controlled by an automatic boost control through the pilot's linkage to maintain the selected manifold pressure during changes in altitude. These valves were only partially open during ground and low level operation to prevent overboosting of the engine. As air density decreased with an increase in altitude, the throttle valves were moved to an open position by boost pressure corresponding to aircraft altitude. This system provided full power within engine boost limitations up to the critical altitude of 26,000 feet (7,900 m). This was the improvement Packard brought to the Merlin.
When the first of the Packard-built Merlins arrived in Britain, the engineers at Rolls-Royce stripped it down and were amazed to find the production-line built Packard engine, far from being as bad as they expected it to be for component tolerances, was actually better.[citation needed] Up until then, R-R Merlins were virtual works of art, with every critical bearing surface being finished off by hand by highly-skilled and experienced craftsmen, and this time-consuming and expensive process placed great strain on the production capability of the workforce involved in the manufacture of these engines. The Packard engine changed many minds, although there were still some at R-R who remained unconvinced of the quality of the American engine, produced as it was by a largely unskilled or semi-skilled workforce (many of whom were female). In the end, the Packard engine's performance removed any doubts about its quality and workmanship.[citation needed]
Following testing of the Merlin in a P51 airframe by the British, the Allison V-1710 was replaced in the North American P-51 Mustang by Packard Merlins, which then became one of the best fighters of the war. It was also incorporated into some models of the Curtiss P-40, specifically the P-40F and P-40L. Packard Merlins powered Canadian-built Hurricane, Lancaster, and Mosquito aircraft, as well as UK-built Spitfires in the shape of the Mark XVI, otherwise the same as the Mark IX with its British-built Merlin.
However, Rolls-Royce's Stanley Hooker (then head of supercharger development) ascribes this improvement in tolerances and true mass-production standards to the involvement of Ford of Britain. After redrafting all the Merlin drawings to their higher standards, Ford were able to produce 400 Merlin engines a week at their factory in Trafford Park, Manchester.[4]
A common misconception is that Packard Merlin engines were used in American PT boats; the engine used was in fact a Packard V-12 engine, a modification of the Liberty L-12, totally unrelated to the Merlin. The possibility is that these engines were also used by British MTBs and MGBs.[5]
Measurement of Boost Pressure
The British measured boost pressure as lbs./sq.inch (or psi). The normal atmospheric pressure at sea level is 14.5 psi, so a reading of +6 means that the air/fuel mix is being compressed by a supercharger blower to 20.5 psi before entering the engine; +25 means that the air/fuel mix is now being compressed to 39.5 psi. The Americans measured their boost ratings using inches of Mercury (" Hg). One pound of boost equals 2.04 inches (52 mm) of Mercury (Hg).
| Inches of Mercury (" Hg) | Pounds of Boost[6] |
| 80" of mercury= | +25 lb boost |
| 67" of mercury= | +18 lb boost |
| 61" of mercury= | +15 lb boost |
| 46" of mercury= | +8 lb boost |
| 44.5" of mercury= | +6 lb boost |
Variants
- V-1650-1: 1,390 hp ( kW); Based on Merlin 28, used in P-40 Kittyhawk and Curtiss XP-60 fighters
- V-1650-3: 1,280 hp ( kW); Based on Merlin 63.
- V-1650-5: 1,400 hp ( kW); Experimental.
- V-1650-7: 1,315 hp ( kW); Similar to Merlin 66.
- V-1650-9: 1,380 hp ( kW); Water methanol injection.
- V-1650-9A: 1,380 hp ( kW);
- V-1650-11: 1,380 hp ( kW); Modified fuel system.
- V-1650-21: 1,380 hp ( kW); Opposite rotation for P-82 Twin Mustang
- V-1650-23:
- V-1650-25:
Applications
- Avro Lancaster
- Bell XP-63
- Curtiss YP-60
- de Havilland Mosquito
- North American XP-78
- P-40F/L Kittyhawk
- P-51 Mustang
- F-82 Twin Mustang
Specifications (V-1650)
General characteristics
- Type: 12-cylinder supercharged liquid-cooled 60° "Vee" piston aircraft engine
- Bore: 5.4 in (137.2 mm)
- Stroke: 6 in (152.4 mm)
- Displacement: 1,648.96 in³ (27.04 L)
- Length: 88.7 in (225.3 cm)
- Width: 30.8 in (78.1 cm)
- Height: 40 in (101.6 cm)
- Dry weight: 1,645 lb (746.5 kg)[7]
Components
- Valvetrain: Overhead camshaft-actuated, two intake and two exhaust valves per cylinder, sodium-cooled exhaust valve stems
- Supercharger: Two-speed two-stage, boost pressure automatically linked to the throttle, water-air aftercooler installed between the second stage and the engine.
- Fuel system: Twin-choke updraft carburettor with automatic mixture control
- Fuel type: 100 Octane from mid 1944 100/150 Grade Aviation fuel
- Oil system: Dry sump with one pressure pump and two scavenge pumps.
- Cooling system: 70% water and 30% ethylene glycol coolant mixture, pressurized.
Performance
- Specific power: 0.95 hp/in³ (43.3 kW/L)
- Compression ratio: 6:1
- Power-to-weight ratio: 0.80 hp/lb (1.76 kW/kg) take-off; 1.21 hp/lb (2.69 kW/kg) 100/150 grade fuel/MS gear.
See also
Related development
Comparable engines
Related lists
References
Notes
- ^ Gunston. Page 144.
- ^ a b Time Magazine (8 July 1940) – Business: Ford's Rolls-Royces. Retrieved: 26 August 2009
- ^ Lumsden 2003, pp. 215–216.
- ^ Not Much Of An Engineer, Sir Stanley Hooker, Airlife Publishing, ISBN 1853102857.
- ^ Packard V-12 PT boat engineRetrieved 7 March 2008
- ^ Gruenhagen 1980 p. 191.
- ^ No coolant or fuel.
Bibliography
- Bridgman, L. (ed.) Jane's fighting aircraft of World War II. London: Crescent, 1998. ISBN 0-517-67964-7
- Fozard, John W (editor).Sydney Camm and the Hurricane; Perspectives on the master fighter designer and his finest achievement. Shrewsbury, Shropshire, UK: Airlife, 1991. ISBN 1-85310-270-9
- Gunston, Bill.World Encyclopaedia of Aero Engines (3rd edition). Sparkford, Somerset, UK: Patrick Stephans Limited, 1995. ISBN 1-85260-509-X
- Hooker, Stanley Not Much of an Engineer London: Airlife, 1984. ISBN 1-85310-285-7
- Harvey-Bailey, A. The Merlin in Perspective - the combat years. Derby, England: Rolls-Royce Heritage Trust, 1983. ISBN 1-872922-06-6
- Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.
- Rubbra, AA. Rolls-Royce piston aero engines: A designer remembers. Derby, England: Rolls-Royce Heritage Trust, 1990. ISBN 1-872922-00-7
External links
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