Packard X-2775: Difference between revisions
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Often called the '''Packard X-2775''', Packard's official designation for this engine was 1A-2775 in 1927 and 1928, and 2A-2775 in 1935. The engine was constructed as a single crankcase with four banks of six cylinders in what is close to an X-configuration. The engine was an upright 60 degree vee-12 and an inverted 60 degree vee-12 sharing a common crankcase. Although technically incorrect, the engine has been characterized as two Packard 1A-1500 V-12 engines coupled with a mutual crankcase. |
Often called the '''Packard X-2775''', Packard's official designation for this engine was 1A-2775 in 1927 and 1928, and 2A-2775 in 1935. The engine was constructed as a single crankcase with four banks of six cylinders in what is close to an X-configuration. The engine was an upright 60 degree vee-12 and an inverted 60 degree vee-12 sharing a common crankcase. Although technically incorrect, the engine has been characterized as two Packard 1A-1500 V-12 engines coupled with a mutual crankcase. |
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==Design and development== |
==Design and development== |
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Packard was founded in 1899 by two brothers, [[James Ward Packard]] (5 November 1863 – 20 March 1928) and [[William Doud Packard]] (November 3, 1861 - November 11, 1923) of Warren, Ohio who ran the [[Packard Electric Company]]. In 1926 about 20 New York business men, including James Packard, and a group of US Navy officers expressed an interest in building an airplane designed to break the standing air speed record. Navy officials agreed that they would finance the proposal when funds became available. The aircraft was to be completed in time to participate in the 1927 [[Schneider Trophy Race]], which would be held in Italy. |
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The 2A-2775's 1900 hp was impressive in 1935, and is rated at about what the USAAC wanted for their XBLR (the XB-15 and XB-16) Long Range Bomber project. |
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The engine was designed by Navy [[Captain Lionel Melville Woolson]], who was an aeronautical engineer at the [[Packard Motor Company]] of Detroit. The engine was an "X" configured design utilizing one upright and one inverted [[Packard 1A-1500]] engine mounted on the same crankshaft within a single crankcase. The 1A-1500 was a 12-cylinder liquid-cooled Vee piston aircraft engine with a 5⅜ in (136.5 mm) bore and 5½ in (140 mm) stroke, with a displacement of 1,498 in³ (24.5 L). In the new engine, it was necessary to shorten the stroke 1/2 inch due to internal clearances. With this 5⅜ in (136.5 mm) bore and 5 inch stroke, the resulting displacement was 2,775 in³. The engineering involved in the design of the crankshaft, single piece crankcase and the master/slave rod system was very complex. |
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The engine was taller than it was wide due to the 60 degree angle at the top and bottom vees. Angles of 60°/120°/60°/120°, with Under-square dimensions (stroke smaller than bore) and light for its horsepower. |
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The connecting rods were a master-slave design similar to that used on a radial engine. This resulted in the 5" stroke becoming slightly longer in three of four banks, and resulted in slightly more displacement than the theoretical 2,722.88 in³ produced by an engine of that bore and stroke. The engine produced 1,250 hp at 2,700 rpm and weighed 1,402 lb. |
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The crank cheeks were used as main bearing journals, and were 7 3/4" in diameter. This was necessary to keep the crankshaft length the same as the 1A-1500 engine so that A1-1500 components could be used, and to keep the weight as low as possible. The single piece crankcase was designed to save weight and give maximum strength, but made assembly of the engine difficult. The engine was finished by August of 1927. |
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Packard supplied a new and very powerful liquid-cooled engine for this project: the Packard X-2775 engine of 1250 hp. In fact this engine consisted of two 625 hp Packard V-1500 V-12 engines coupled with a mutual crankcase with one part upright and the other one inverted to form a 24-cylinder X-type engine with four rows of six cylinders. |
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The Navy's Bureau of Aeronautics ordered a second supercharged engine under their original contract No. 3224. It was equipped with a special Roots-type supercharger. It was ordered with a supercharger when it was discovered that it would be necessary to supercharge the engine in order to equal the reported speeds of the other contestants. |
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The new Kirkham-William racer was the most powerful biplane racer ever built for the Schneider Cup event. |
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The Bureau of Aeronautics analyzed the possibilities of the plane becoming a competitive race plane, and decided that the extra weight of the supercharger could be better put to use by installing an epicyclic reduction gear, for improved propeller efficiency, thereby providing greater improvement in performance than what the supercharged engine with a direct drive propeller could provide for the same weight. |
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The racing team was, however, not very lucky with the new racer since it only accumulated a very flew flying hours before the race in Venice. They asked the organizing committee for a time extension, but because this was not granted the entry for the race had to be withdrawn. It was later converted to a landplane with a fixed wheel undercarriage and managed to set a new world-speed record of 519 km/h but this record was never officially recognized. |
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It was further planned to increase the compression ratio of the engine, improving its performance with no increase in weight, but needed to secure dynamometer data on the supercharged engine to make a final decision. The dynomometer tests indicated the power output was only 1,300 hp @ 2,800 rpm due to the large impeller clearance that allowed only 7.7 in Hg. boost. After reducing the impeller clearances, the supercharger then produced 9.6 in Hg of boost and the engine produced 1,500 hp @ 2,700 rpm. |
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After the failure of the Kirkham-Williams biplane racer to perform in the 1927 Schneider Cup race, the Americans made a last attempt for the 1929 race at Calshot, U.K. The original biplane racer was totally redesigned into a mid-wing monoplane racer with an even more powerful Packard X- 2775 engine producing 1500 hp. It was named Mercury I. The work was done by the Naval Aircraft Factory at Philadelphia under great secrecy. Racing Pilot Al Williams was again a leading individual in this project. Great care was taken for aerodynamic shaping of the racer using wind-tunnel data from tests with scale models and the result was an extremely good-looking racer. |
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The first engine later received a epicyclic propeller reduction gear made by Allison, an increase in its compression ratio, a Scintilla magneto ignition, and the new design cylinder banks of the 3A-1500 inverted engines, a design that had both spark plugs on the outside for easier maintenance. |
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Upon completion, Al Williams did the initial flight- testing with the lower rated engine from the biplane racer near the Santee Wharf of the Annapolis Military Academy. Because the both floats were buried very deep in the water, and the torque of the big Packard engine produced a tendency for the left wing to dig into the water he hardly managed to become airborne in the plane because the use of full rudder and ailerons to keep the plane on a straight course produced too much drag. He was also troubled by water spray hitting the propeller and fuselage. He finally managed to make a short hop with the Mercury but because of a fuel pressure drop he had to land on the water again, resulting in bending the propeller. In spite of these problems, the Mercury was a very promising type and the disappointment of Williams’s group must have been great when the U.S. Navy declined a request to transport the Mercury by vessel to the U.K! |
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Official Packard photographs of this engine are marked "model 2A-2775", and photographs of the earlier versions are marked "not to be released to the press — hereafter only 2A-2775 are to be released — per Capt. Woolson." Most of the published photographs are of this engine. In spite of Captain Woolson's note, it was identified as either a 1A-2775 or the "Packard X engine." |
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Compare Buzzard/R with later Griffon in terms of weight. 1140lb/517kg for the Buzzard, 1640lb/744kg for the R (including that massive supercharger with double sided impeller) and the Griffon 65 at 1980lb/900kg. |
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The engine was advertised as being available "built-to-order" as late as September of 1930 at $35,000 each. No orders were received, and because only two engines were built, both for the Navy as X-2775s, the Packard model designation of 2A-2775 never came into public use. |
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Engine No. 2 also received the new style cylinder banks and was tested both with and without the reduction gear. The direct drive and reduction gear units were interchangeable, and were switched between the two engines as needed. |
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Engine No. 1 in its most modified version, with high compression, reduction gear and late type cylinder banks, was used in the "Mercury" racing plane with engine 1A-2775, Serial No. 1, Bureau No. 10960, as a U. S. entry in the 1929 Schneider Trophy. |
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Engine No. 1 is the only known 1A-2775 survivor and it was given by the Navy to the Smithsonian in 1971. It is in the same configuration as it was when used in the Mercury racer. |
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The 2A-2775 Engine |
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Packard apparently built a third engine some time after 1931 when the Navy had stopped testing its engines. No photographs of this engine have been found, but engineering data dated in early 1939 show a 2A-2775 with an output of 1,900 hp @ 2,800 rpm. BMEP was listed as 196 and would indicate the engine was supercharged. |
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Revision as of 03:39, 20 July 2011
| Packard 1A-2775 | |
|---|---|
| Type | 24-cylinder liquid cooled X-configured piston engine |
| National origin | USA |
| Manufacturer | Packard Motor Car Company |
| First run | 1927 |
| Produced | 1927-1935 |
| Number built | 3 |
| Developed from | 1A-1500 |
Often called the Packard X-2775, Packard's official designation for this engine was 1A-2775 in 1927 and 1928, and 2A-2775 in 1935. The engine was constructed as a single crankcase with four banks of six cylinders in what is close to an X-configuration. The engine was an upright 60 degree vee-12 and an inverted 60 degree vee-12 sharing a common crankcase. Although technically incorrect, the engine has been characterized as two Packard 1A-1500 V-12 engines coupled with a mutual crankcase.
Design and development
Packard was founded in 1899 by two brothers, James Ward Packard (5 November 1863 – 20 March 1928) and William Doud Packard (November 3, 1861 - November 11, 1923) of Warren, Ohio who ran the Packard Electric Company. In 1926 about 20 New York business men, including James Packard, and a group of US Navy officers expressed an interest in building an airplane designed to break the standing air speed record. Navy officials agreed that they would finance the proposal when funds became available. The aircraft was to be completed in time to participate in the 1927 Schneider Trophy Race, which would be held in Italy.
The engine was designed by Navy Captain Lionel Melville Woolson, who was an aeronautical engineer at the Packard Motor Company of Detroit. The engine was an "X" configured design utilizing one upright and one inverted Packard 1A-1500 engine mounted on the same crankshaft within a single crankcase. The 1A-1500 was a 12-cylinder liquid-cooled Vee piston aircraft engine with a 5⅜ in (136.5 mm) bore and 5½ in (140 mm) stroke, with a displacement of 1,498 in³ (24.5 L). In the new engine, it was necessary to shorten the stroke 1/2 inch due to internal clearances. With this 5⅜ in (136.5 mm) bore and 5 inch stroke, the resulting displacement was 2,775 in³. The engineering involved in the design of the crankshaft, single piece crankcase and the master/slave rod system was very complex.
The connecting rods were a master-slave design similar to that used on a radial engine. This resulted in the 5" stroke becoming slightly longer in three of four banks, and resulted in slightly more displacement than the theoretical 2,722.88 in³ produced by an engine of that bore and stroke. The engine produced 1,250 hp at 2,700 rpm and weighed 1,402 lb.
The crank cheeks were used as main bearing journals, and were 7 3/4" in diameter. This was necessary to keep the crankshaft length the same as the 1A-1500 engine so that A1-1500 components could be used, and to keep the weight as low as possible. The single piece crankcase was designed to save weight and give maximum strength, but made assembly of the engine difficult. The engine was finished by August of 1927.
The Navy's Bureau of Aeronautics ordered a second supercharged engine under their original contract No. 3224. It was equipped with a special Roots-type supercharger. It was ordered with a supercharger when it was discovered that it would be necessary to supercharge the engine in order to equal the reported speeds of the other contestants.
The Bureau of Aeronautics analyzed the possibilities of the plane becoming a competitive race plane, and decided that the extra weight of the supercharger could be better put to use by installing an epicyclic reduction gear, for improved propeller efficiency, thereby providing greater improvement in performance than what the supercharged engine with a direct drive propeller could provide for the same weight.
It was further planned to increase the compression ratio of the engine, improving its performance with no increase in weight, but needed to secure dynamometer data on the supercharged engine to make a final decision. The dynomometer tests indicated the power output was only 1,300 hp @ 2,800 rpm due to the large impeller clearance that allowed only 7.7 in Hg. boost. After reducing the impeller clearances, the supercharger then produced 9.6 in Hg of boost and the engine produced 1,500 hp @ 2,700 rpm.
The first engine later received a epicyclic propeller reduction gear made by Allison, an increase in its compression ratio, a Scintilla magneto ignition, and the new design cylinder banks of the 3A-1500 inverted engines, a design that had both spark plugs on the outside for easier maintenance.
Official Packard photographs of this engine are marked "model 2A-2775", and photographs of the earlier versions are marked "not to be released to the press — hereafter only 2A-2775 are to be released — per Capt. Woolson." Most of the published photographs are of this engine. In spite of Captain Woolson's note, it was identified as either a 1A-2775 or the "Packard X engine."
The engine was advertised as being available "built-to-order" as late as September of 1930 at $35,000 each. No orders were received, and because only two engines were built, both for the Navy as X-2775s, the Packard model designation of 2A-2775 never came into public use.
Engine No. 2 also received the new style cylinder banks and was tested both with and without the reduction gear. The direct drive and reduction gear units were interchangeable, and were switched between the two engines as needed.
Engine No. 1 in its most modified version, with high compression, reduction gear and late type cylinder banks, was used in the "Mercury" racing plane with engine 1A-2775, Serial No. 1, Bureau No. 10960, as a U. S. entry in the 1929 Schneider Trophy.
Engine No. 1 is the only known 1A-2775 survivor and it was given by the Navy to the Smithsonian in 1971. It is in the same configuration as it was when used in the Mercury racer.
The 2A-2775 Engine
Packard apparently built a third engine some time after 1931 when the Navy had stopped testing its engines. No photographs of this engine have been found, but engineering data dated in early 1939 show a 2A-2775 with an output of 1,900 hp @ 2,800 rpm. BMEP was listed as 196 and would indicate the engine was supercharged.
Variants
- 1A-2775
- rated at 1200 hp (894 kw) at 2600 rpm and max of 1250 hp (932nbsp;kw)at 2700 rpm Weight 1513 lb (691 kg)
- 1A-2775
- rated at 1400 hp (1044 kW) at 2600 rpm and max of 1500 hp (1119 kW) at 2700 rpm - Weight: 1635lb (742 kg) - Supercharged (1928)
- 2A-2775
- rated at 1900 hp (1417 kW) at 2800 rpm-Weight: 1722lb/781kg- Supercharged (1935)
Specifications (variant)
General characteristics
- Type: 24-cylinder, liquid-cooled, X-configured, piston engine
- Bore: 5 3/8 in (136.525 mm)
- Stroke: 4 in (127 mm)
- Displacement: 2723 in³ (44.6 L)
- Dry weight: 1635 lb (742 kg)
Components
- Valvetrain: 4-valve, overhead-cam
- Supercharger: Gear-driven supercharger
Performance
- Power output: 1400 hp (1044 kW) at 2600 rpm
- Specific power: .50 hp/in³
- Power-to-weight ratio: .85 hp/lb
References
External links