The Wright R-3350 Duplex-Cyclone is an American twin-row,

supercharge In theoretical physics, a supercharge is a generator of supersymmetry transformations. It is an example of the general notion of a charge in physics. Supercharge, denoted by the symbol Q, is an operator which transforms bosons into fermions, and v ...

d, air-cooled,

radial Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric) In mathematics, physics, and engineering, a Euclidean vector or simply a vector (sometimes called a geometric vector or spatial vector) ...

aircraft engine with 18

cylinders A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infini ...

displacing nearly . Power ranged from 2,200 to over 3,700 hp (1,640 to 2,760 kW), depending on the model. Developed before

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, the R-3350's design required a long time to mature before finally being used to power the

Boeing B-29 Superfortress The Boeing B-29 Superfortress is an American four-engined propeller-driven heavy bomber, designed by Boeing and flown primarily by the United States during World War II and the Korean War. Named in allusion to its predecessor, the B-17 Fl ...

. After the war, the engine had matured sufficiently to become a major civilian airliner design, notably in its

turbo-compound A turbo-compound engine is a reciprocating engine that employs a turbine to recover energy from the exhaust gases. Instead of using that energy to drive a turbocharger as found in many high-power aircraft engines, the energy is instead sent to ...

forms, and was used in the

Lockheed L-1049 Super Constellation The Lockheed L-1049 Super Constellation is an American aircraft, a member of the Lockheed Constellation aircraft line. The L-1049 was Lockheed's response to the successful Douglas DC-6 airliner, first flying in 1950. The aircraft was also produc ...

airliners into the 1990s. The engine is commonly used on

Hawker Sea Fury The Hawker Sea Fury is a British fighter aircraft designed and manufactured by Hawker Aircraft. It was the last propeller-driven fighter to serve with the Royal Navy, and one of the fastest production single reciprocating engine aircraft e ...

and

Grumman F8F Bearcat The Grumman F8F Bearcat is an American single-engine carrier-based fighter aircraft introduced in late World War II. It served during the mid-20th century in the United States Navy, the United States Marine Corps, and the air forces of other n ...

Unlimited Class Racers at the

Reno Air Races The Reno Air Races, officially known as the STIHL National Championship Air Races from 2016, is a multi-day event tailored to the aviation community that takes place each September at the Reno Stead Airport a few miles north of Reno, Nevada. A ...

. Its main rival was the ,

Pratt & Whitney R-4360 Wasp Major The Pratt & Whitney R-4360 Wasp Major is an American 28-cylinder four-row radial piston aircraft engine designed and built during World War II. First run in 1944, at , it is the largest-displacement aviation piston engine to be mass-produced in ...

, first run some seven years after the Duplex-Cyclone's beginnings.

Design and development

In 1927,

Wright Aeronautical Wright Aeronautical (1919–1929) was an American aircraft manufacturer headquartered in Paterson, New Jersey. It was the successor corporation to Wright-Martin. It built aircraft and was a supplier of aircraft engines to other builders in the g ...

introduced its famous "Cyclone" engine, which powered a number of designs in the 1930s. After merging with Curtiss to become

Curtiss-Wright The Curtiss-Wright Corporation is a manufacturer and services provider headquartered in Davidson, North Carolina, with factories and operations in and outside the United States. Created in 1929 from the consolidation of Curtiss, Wright, and v ...

in 1929, an effort was started to redesign the engine to the class. The new

Wright R-1820 Cyclone 9 The Wright R-1820 Cyclone 9 is an American radial engine developed by Curtiss-Wright, widely used on aircraft in the 1930s through 1950s. It was produced under license in France as the Hispano-Suiza 9V or Hispano-Wright 9V, and in the Soviet Uni ...

first ran successfully in 1935, and became one of the most-used aircraft engines in the 1930s and WWII, powering all frontline examples (the -C through -G models) of the

B-17 Flying Fortress The Boeing B-17 Flying Fortress is a four-engined heavy bomber developed in the 1930s for the United States Army Air Corps (USAAC). Relatively fast and high-flying for a bomber of its era, the B-17 was used primarily in the European Theater ...

heavy bomber aircraft serving in the war, each powerplant assisted by a

General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...

-designed

turbocharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

for maximum power output at high altitudes. By 1931

Pratt & Whitney Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of Raytheon Technologies. Pratt & Whitney's aircraft engines are widely used in both civil aviation (especially airlines) and military aviat ...

had started a development of their equally famous single-row,

Wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. Th ...

nine-cylinder design into a larger and much more powerful fourteen-cylinder, twin-row design — the

R-1830 Twin Wasp The Pratt & Whitney R-1830 Twin Wasp is an American air-cooled radial aircraft engine. It displaces and its bore and stroke are both . The design traces its history to 1929 experiments at Pratt & Whitney on twin-row designs. Production began ...

— of a nearly identical 30-liter displacement figure, that would easily compete with this larger, single-row Cyclone. In 1935 Wright followed P&W's lead, and developed much larger engines based on the mechanics of the Cyclone. The result was two designs with a somewhat shorter stroke, a 14-cylinder design of almost 43 liters displacement that would evolve into the

Wright R-2600 Twin Cyclone The Wright R-2600 Cyclone 14 (also called Twin Cyclone) is an American radial engine developed by Curtiss-Wright and widely used in aircraft in the 1930s and 1940s. History In 1935, Curtiss-Wright began work on a more powerful version of their ...

, and a much larger 18-cylinder design that became the R-3350. A larger twin-row 22-cylinder version, the

Wright R-4090 Cyclone 22 The R-4090 Cyclone 22 was an experimental radial piston engine designed and built in prototype form in the United States during the 1940s. Design and development During the 1940s, Wright Aeronautical Corporation was constantly in competition wit ...

, was experimented with as a competitor to the 71.5 liter-displacement four-row, 28-cylinder

, but was not produced. With Pratt & Whitney starting development of their own 46 liter-displacement 18-cylinder, twin-row high-output radial as the

Pratt & Whitney R-2800 Double Wasp The Pratt & Whitney R-2800 Double Wasp is an American twin-row, 18-cylinder, air-cooled radial aircraft engine with a displacement of , and is part of the long-lived Wasp family of engines. The R-2800 saw widespread use in many important A ...

in 1937, Wright's first R-3350 prototype engines — itself having a nearly 55 liter displacement figure — were initially run in May of the same year. Continued development was slow, both due to the complex nature of the engine, as well as the R-2600 receiving considerably more attention. The R-3350 did not fly until 1941, after the prototype

Douglas XB-19 The Douglas XB-19 was a four-engined, piston-driven heavy bomber produced by the Douglas Aircraft Company for the United States Army Air Forces (USAAF) during the early 1940s. It was the largest bomber built for the USAAF until 1946, and was or ...

had been redesigned from the

Allison V-3420 The Allison V-3420 was a large experimental piston aircraft engine, designed in 1937 by the American Allison Engine Company. Design and development In 1937, at the behest of the United States Army Air Corps, the Allison Engine Company agreed t ...

to accept the R-3350. Things changed dramatically in 1940 with the introduction of a new contract by the

USAAC The United States Army Air Corps (USAAC) was the aerial warfare service component of the United States Army between 1926 and 1941. After World War I, as early aviation became an increasingly important part of modern warfare, a philosophical r ...

to develop a long-range bomber capable of flying from the US to Germany with a 20,000 lb (9000 kg) bomb load. Although smaller than the Bomber D designs that led to the

, the new designs required roughly the same amount of power. When preliminary designs were returned in the summer of 1940, three of the four designs were based on the R-3350. Suddenly the engine was seen as the future of army aviation, and serious efforts to get the design into production started. In 1942

Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automoti ...

started the construction of the

Dodge Chicago Plant The Dodge Chicago Aircraft Engine Plant was a World War II defense plant that built the majority of the B-29 bomber aircraft engines used in World War II. The plant design was initiated by automotive plant designer Albert Kahn and his company. Th ...

and the new factory, designed by Albert Kahn, was in full operation by early 1944. Wright R-3350 Cyclone Engine 1

By 1943 the ultimate development of the new bomber program, the Boeing B-29 Superfortress, was flying. The engines remained temperamental, and showed an alarming tendency for the rear cylinders to overheat, partially due to minimal clearance between the cylinder baffles and the cowl. A number of changes were introduced into the Superfortress' production line to provide more cooling at low speeds, with the aircraft rushed into operational use in the Pacific in 1944. This proved unwise, as the early B-29 tactics of maximum weights, when combined with the high temperatures of the tropical airfields where B-29s were based, produced overheating problems that were not completely solved, and the engines having an additional tendency to swallow their own valves. Because of a high

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

content in the potentially combustible crankcase alloy, the resulting engine fires — sometimes burning with a core temperature approaching 5,600 °F (3,100 °C) — were often so intense the main

spar SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...

could burn through in seconds, resulting in catastrophic wing failure. Early versions of the R-3350 had carburetors, though the poorly-designed elbow entrance to the supercharger led to serious problems with fuel/air distribution. Near the end of WWII, the system was changed to use

gasoline direct injection Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct fro ...

where fuel was injected directly into the combustion chamber. This improved engine reliability. After the war the engine was redesigned and became popular for large aircraft, notably the

Lockheed Constellation The Lockheed Constellation ("Connie") is a propeller-driven, four-engined airliner built by Lockheed Corporation starting in 1943. The Constellation series was the first pressurized-cabin civil airliner series to go into widespread use. Its press ...

and

Douglas DC-7 The Douglas DC-7 is an American transport aircraft built by the Douglas Aircraft Company from 1953 to 1958. A derivative of the DC-6, it was the last major piston engine-powered transport made by Douglas, being developed shortly after the ear ...

. Following the war, the

Turbo-Compound A turbo-compound engine is a reciprocating engine that employs a turbine to recover energy from the exhaust gases. Instead of using that energy to drive a turbocharger as found in many high-power aircraft engines, the energy is instead sent to ...

Gunston 2006, p. 247. system was developed to deliver better fuel efficiency. In these versions, three power-recovery

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...

s (PRT) were inserted into the exhaust piping of each group of six cylinders, and geared to the engine crankshaft by

fluid coupling A fluid coupling or hydraulic coupling is a hydrodynamic or 'hydrokinetic' device used to transmit rotating mechanical power.

s to deliver more power. The PRTs recovered about 20% of the exhaust energy (around ) that would have otherwise been wasted, but reduced engine reliability (Mechanics tended to call them Parts Recovery Turbines, since increased exhaust heat meant a return of the old habit of the engine destroying exhaust valves). The fuel burn for the PRT-equipped aircraft was nearly the same as the older Pratt and Whitney R-2800, while producing more useful power. Effective 15 October 1957 a DA-3/DA-4 engine cost $88,200. By this point reliability had improved with the mean time between overhauls at 3,500 hours and specific fuel consumption in the order of 0.4 lb/hp/hour (243 g/kWh, giving a 34% fuel efficiency). Engines in use as of the 2020s are limited to

manifold pressure Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere. Manifold vacuum is an effect of a piston's movement on the induction stroke and the ...

, giving with 100/130 octane fuel (or 100LL) instead of the and possible with 115/145, or better, octane fuels, which are no longer available because such formulations are exceedingly toxic due to the extremely high

tetraethyllead Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb( C2H5)4. It is a fuel additive, first being mixed with gasoline beginning in the 1920s as a patented octane rating booster that al ...

content of these avgas versions. Several racers at the

use R-3350s. Modifications on one,

Rare Bear ''Rare Bear'' is a highly modified Grumman F8F Bearcat that dominated the Reno Air Races for decades. History The Bearcat that became Rare Bear was a severely damaged wreck when discovered by Lyle Shelton in 1969. It had been abandoned next ...

, include a nose case designed for a slow-turning prop, taken from a R-3350 used on the

Lockheed L-1649 Starliner The Lockheed L-1649 Starliner was the last model of the Lockheed Constellation line of airliners. Powered by four Wright R-3350 TurboCompound engines, it was built at Lockheed's Burbank, California plant from 1956 to 1958. Design and developme ...

, mated to the power section (crankcase, crank, pistons, and cylinders) taken from a R-3350 used on the

. The supercharger is taken from a R-3350 used on the

Lockheed EC-121 The Lockheed EC-121 Warning Star was an American airborne early warning and control radar surveillance aircraft operational in the 1950s in both the United States Navy (USN) and United States Air Force (USAF). The military version of the Lock ...

and the engine is fitted with

nitrous oxide Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a ...

injection. Normal rated power of a stock R-3350 is at 2,600 rpm and of manifold pressure. With these modifications, Rare Bear's engine produces at 3,200 rpm and of manifold pressure, and with nitrous oxide injection.

Variants

;R-3350-13: ;R-3350-23: ;R-3350-24W: ;R-3350-26W: ;R-3350-30W: ;R-3350-30WA: ;R-3350-32W: ;R-3350-34: ;R-3350-35A: ;R-3350-42WA: ;R-3350-53: ;R-3350-57: ;R-3350-85: ;R-3350-89A: ;R-3350-93W: ;972TC18DA1:Commercial equivalent to the -30W without water injection ;956C18CA1:Commercial, similar to the -26W ;975C18CB1:Commercial, similar to the 956C18CA1

Applications

Engines on display

* Wright R-3350-89 is on public display at the

Aerospace Museum of California The Aerospace Museum of California is a private non-profit aviation museum located in North Highlands, California, outside of Sacramento, California, on the grounds of the former McClellan Air Force Base. The museum has a 4.5-acre outdoor Air Park ...

* Wright R-3350 is on public display at

Flyhistorisk Museum, Sola Flyhistorisk Museum, Sola (Sola Aviation Museum) is an aviation museum located in Stavanger Airport, Sola, near Stavanger, Norway. The museum was founded in 1984 and is run by local volunteers. Flyhistorisk Museum, Sola went into cooperation ...

, near

Stavanger Stavanger (, , American English, US usually , ) is a city and municipalities of Norway, municipality in Norway. It is the fourth largest city and third largest metropolitan area in Norway (through conurbation with neighboring Sandnes) and the a ...

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

* Wright R-3350-35A is on public display at Texas Air Museum - Stinson Chapter,

San Antonio ("Cradle of Freedom") , image_map = , mapsize = 220px , map_caption = Interactive map of San Antonio , subdivision_type = Country , subdivision_name = United States , subdivision_type1= U.S. state, State , subdivision_name1 = Texas , s ...

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

File:Air Zoo December 2019 148 (Wright R-3350 Turbo-Compound Duplex Cyclone).jpg, R-3350 on display at the

Air Zoo The Air Zoo, founded as the Kalamazoo Aviation History Museum, is an aviation museum and indoor amusement park next to the Kalamazoo-Battle Creek International Airport in Portage, Michigan. The Air Zoo holds many historical and rare aircraft, inc ...

File:20-09-094-R 3350.jpg, R-3350 on display at Museum of Aviation,

Robins AFB Robins Air Force Base is a major United States Air Force installation located in Houston County, Georgia, United States. The base is located just east of the city of Warner Robins, south-southeast of Macon and approximately south-southeast ...

Specifications (R-3350-C18-BA)

References

Notes

Bibliography

*Gunston, Bill. ''World Encyclopedia of Aero Engines: From the Pioneers to the Present Day''. 5th edition, Stroud, UK: Sutton, 2006. *White, Graham. ''Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II''. Warrendale, Pennsylvania: SAE International, 1995. * ''Jane's Fighting Aircraft of World War II''. London. Studio Editions, 1998. .

External links

Wright R-3350-57 Cyclone Fact Sheets from the National Museum of the USAF website

1940s film on Chrysler production of Wright's Duplex-Cyclone radials for the Superfortress
google books AIR CORPS technical report
150 hour test of wright 3350-19 with bendix feul injection 1943
{{US military piston aeroengines 1930s aircraft piston engines Aircraft air-cooled radial piston engines Turbo-compound engines R-3350