1937 18-cylinder radial piston engine family by Wright
The
Wright R-3350 Duplex-Cyclone
is an American twin-row,
supercharged
, air-cooled,
radial
aircraft engine with 18
cylinders
displacing nearly 3,350 cubic inches (54.9 L). 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
, the R-3350's design required a long time to mature before finally being used to power the
Boeing B-29 Superfortress
.
After the war, the engine had matured sufficiently to become a major civilian airliner design, notably in its
turbo-compound
forms, and was used in the
Lockheed L-1049 Super Constellation
airliners into the 1950s. Its main rival was the 4,360 in
3
(71.4 L), 4,300 hp (3,200 kW)
Pratt & Whitney R-4360 Wasp Major
, first run some seven years after the Duplex-Cyclone's beginnings. The engine is commonly used on
Hawker Sea Fury
and
Grumman F8F Bearcat
Unlimited Class Racers at the
Reno Air Races
.
Design and development
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In 1927,
Wright Aeronautical
introduced its famous "Cyclone" engine, which powered a number of designs in the 1930s. After merging with Curtiss to become
Curtiss-Wright
in 1929, an effort was started to redesign the engine to the 1,000 horsepower (750 kW) class. The new
Wright R-1820 Cyclone 9
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
heavy bomber aircraft serving in the war, each powerplant assisted by a
General Electric
-designed
turbocharger
for maximum power output at high altitudes.
By 1931
Pratt & Whitney
had started a development of their equally famous single-row,
Wasp
nine-cylinder design into a larger and much more powerful fourteen-cylinder, twin-row design ? the
R-1830 Twin Wasp
? 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
, 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
, was experimented with as a competitor to the 71.5 liter-displacement four-row, 28-cylinder
Pratt & Whitney R-4360 Wasp Major
, 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
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
had been redesigned from the
Allison V-3420
to accept the R-3350.
Things changed dramatically in 1940 with the introduction of a new contract by the
USAAC
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 Douglas XB-19, 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
started the construction of the
Dodge Chicago Plant
and the new factory, designed by
Albert Kahn
, was in full operation by early 1944.
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
content in the potentially combustible crankcase alloy, the resulting engine fires ? sometimes burning with a core temperature approaching 5,600 °F (3,100 °C)
[2]
? were often so intense the main
spar
could burn through in seconds, resulting in catastrophic wing failure.
[3]
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
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
and
Douglas DC-7
.
Following the war, the
Turbo-Compound
[4]
system was developed to deliver better
fuel efficiency
. In these versions, three power-recovery
turbines
(PRT) were inserted into the exhaust piping of each group of six cylinders, and geared to the engine crankshaft by
fluid couplings
to deliver more power. The PRTs recovered about 20% of the exhaust energy (around 450 horsepower (340 kW)) 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.
[5]
Effective 15 October 1957 a DA-3/DA-4 engine cost $88,200.
[6]
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 52 inHg (180 kPa)
manifold pressure
, giving 2,880 horsepower (2,150 kW) with 100/130 octane fuel (or 100LL) instead of the 59.5 inHg (201 kPa) and 3,400 horsepower (2,500 kW) 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
content of these
avgas versions
.
Several racers at the
Reno Air Races
use R-3350s. Modifications on one,
Rare Bear
, include a nose case designed for a slow-turning prop, taken from an R-3350 used on the
Lockheed L-1649 Starliner
, mated to the power section (crankcase, crank, pistons, and cylinders) taken from an R-3350 used on the Douglas DC-7. The supercharger is taken from an R-3350 used on the
Lockheed EC-121
and the engine is fitted with
nitrous oxide
injection. Normal rated power of a stock R-3350 is 2,800 horsepower (2,100 kW) at 2,600 rpm and 45 inHg (150 kPa) of manifold pressure. With these modifications,
Rare Bear
'
s engine produces 4,000 horsepower (3,000 kW) at 3,200 rpm and 80 inHg (270 kPa) of manifold pressure, and 4,500 horsepower (3,400 kW) with nitrous oxide injection.
[7]
Variants
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- R-3350-13
- 2,200
shp
(1,640 kW)
- R-3350-23
- 2,200 shp (1,640 kW)
- R-3350-24W
- 2,500 shp (1,860 kW)
- R-3350-26W
- 2,800 shp (2,090 kW)
- R-3350-30W
- R-3350-30WA
- R-3350-32W
- 3,700 shp (2,760 kW)
- R-3350-34
- 3,400 shp (2,540 kW)
- R-3350-35A
- 2,200 shp (1,640 kW)
- R-3350-41
- Fuel injected
Silverplate
variant
[8]
- R-3350-42WA
- 3,800 shp (2,830 kW)
- R-3350-53
- 2,700 shp (2,010 kW)
- R-3350-57
- 2,200 shp (1,640 kW)
- R-3350-85
- 2,500 shp (1,860 kW)
- R-3350-89A
- 3,500 shp (2,610 kW)
- R-3350-93W
- 3,500 shp (2,610 kW)
- 972TC18DA1
- Commercial equivalent to the -30W without water injection
- 956C18CA1
- Commercial, similar to the -26W
- 975C18CB1
- Commercial, similar to the 956C18CA1
Applications
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Engines on display
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Specifications (R-3350-C18-BA)
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Data from
Jane's
.
[9]
General characteristics
- Type:
Twin-row 18-cylinder
radial engine
- Bore
:
6
+
1
⁄
8
in (155.6 mm)
- Stroke
:
6
+
5
⁄
16
in (160.3 mm)
- Displacement
:
3,347.9 in
3
(54.862 L)
- Length:
76.26 inches (1,937 mm)
- Diameter:
55.78 inches (1,417 mm)
- Dry weight
:
2,670 pounds (1,210 kg)
Components
Performance
See also
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Related development
Comparable engines
Related lists
References
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Notes
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Bibliography
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- Gunston, Bill.
World Encyclopedia of Aero Engines: From the Pioneers to the Present Day
. 5th edition, Stroud, UK: Sutton, 2006.
ISBN
0-7509-4479-X
- 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.
ISBN
1-56091-655-9
- Jane's Fighting Aircraft of World War II
. London. Studio Editions, 1998.
ISBN
0-517-67964-7
.
- Doyle, David. "B-29 Superfortress Vol. 1" Schiffer Publishing Ltd. 2020
ISBN
978-0-7643-5937-8
External links
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