In 1927,
Wright Aeronautical introduced its "Cyclone" engine, which powered several designs in the 1930s. After merging with Curtiss to become
Curtiss-Wright in 1929, an effort was started to design an engine in the class. The new
Wright R-1820 Cyclone 9 first ran in 1935, and became one of the most used aircraft engines in the late 1930s and early 1940's, powering the
Boeing B-17 Flying Fortress heavy bomber,
General Motors FM-2 Wildcat fighter and
Douglas SBD Dauntless dive bomber, among many others. By 1931
Pratt & Whitney had started a development of their single-row
Wasp nine-cylinder engine into the larger and much more powerful fourteen-cylinder, twin-row
R-1830 Twin Wasp with a similar displacement that would easily compete with the single-row Cyclone. In 1935, Wright followed P&W's lead and developed larger engines based on the Cyclone. The result was two designs, a 14-cylinder short stroke design of nearly 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 displacement four-row, 28-cylinder
Pratt & Whitney R-4360 Wasp Major, but was not produced. With Pratt & Whitney starting development of their own displacement 18-cylinder, twin-row radial as the
R-2800 Double Wasp in 1937, Wright's first R-3350 prototype engines with a displacement were run in May of the same year. Development was slow due to the complexity, and the R-2600 received development priority. The R-3350 did not fly until 1941, after the
Douglas XB-19 had been redesigned to use R-3350s instead of
Allison V-3420 inlines. 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 of bombs. Although smaller than the Bomber D designs that led to the Douglas XB-19, the new designs required just as much power. When four preliminary designs were presented in mid-1940, three of them used the R-3350. Suddenly, development was a priority, and serious efforts to get it into production began. In 1942,
Chrysler started building the
Dodge Chicago Plant, which was ready by early 1944. By 1943, the new Boeing B-29 Superfortress was flying with R-3350s. The engines remained temperamental, and the rear cylinders tended to overheat, partially due to inadequate clearance between the cylinder baffles and the cowl.
A number of changes were introduced to improve cooling, and the aircraft was rushed into service in the Pacific in 1944. This proved unwise, as the early B-29s taking off at maximum weights, in the high temperature conditions of the B-29's tropical airfields, caused overheating that was not completely solved, and the engines also had a tendency to swallow valves. Because of a high
magnesium content in the crankcase, engine fires could burn with a core temperature approaching which could burn through the main
spar in seconds, causing a catastrophic failure. Early R-3350s used
carburetors, though the poorly designed elbow entrance to the supercharger led to serious problems with fuel/air mixtures. Near the end of WWII, the system was changed to use
gasoline direct injection, which improved 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 system was developed to deliver better
fuel efficiency. In these versions, three power-recovery
turbines (PRT) were inserted into the exhaust of each group of six cylinders, and geared to the crankshaft by
fluid couplings to deliver more power. Compared with a similar non-turbocompounded R-3350, turbocompounding added about at take-off power and at cruise settings. 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. Turbo-compound R-3350s could achieve
specific fuel consumption as low as 0.4 lb/hp/hour (243 g/kWh). ==Variants==