Shvetsov ASh-73

ASh-73
Type	Radial engine
National origin	Soviet Union
Manufacturer	Shvetsov OKB-19 in Perm'
First run	1946
Major applications	Tupolev Tu-4, Beriev Be-6
Number built	14,310
Developed from	Shvetsov M-71 Shvetsov M-72

The Shvetsov ASh-73 was an 18-cylinder, air-cooled, radial aircraft engine produced between 1947 and 1957 in the Soviet Union. It was primarily used as the powerplant for the Tupolev Tu-4 heavy bomber, a copy of the American Boeing B-29 Superfortress.

The Shvetsov ASh-73 originated in 1938 from a specification for an 18-cylinder, twin-row, development of the Shvetsov M-25, a license-built 9-cylinder, air-cooled, radial Wright R-1820-F3 Cyclone engine. Development continued through a series of less than successful engines, before culminating in the ASh-73. Contrary to popular belief the ASh-73 wasn't a reverse engineered copy of the Wright R-3350 Duplex Cyclone: "There was no need to copy the Wright R-3350-23A; the engine that was put into production was the indigenous ASh-73TK - a further development of the M-71 and M-72, which differed in being fitted with twin TK-19 turbosuperchargers (TK = toorbokompressor)." rather the ASh-73 was the product of a similar specification. Since the earlier M-25 engines were a licensed copy of the Wright R-1820, there were similarities and some parts were interchangeable between the Duplex Cyclone and the ASh-73 powerplants. The two engines evolved from a common ancestor and to a similar requirement. "In the late 1930s and the early 1940s OKB-19 evolved two 18-cylinder two-row radials — the 2,000-hp M-71 and the 2,250-hp M-72 — which were similar in their design features and production techniques to the Wright Duplex Cyclone engines powering the B-29."

The progenitor for the ASh-73 was the M-70. It was tested in late 1938 and was a failure because of cracks in the master connecting rod and the geared centrifugal supercharger's impeller. The exhaust valves also burnt through. The M-71 of 1939 was the successor to the M-70 and it too was not a success. It used some components from the M-62 engine, but its development was slowed by the German attack on the Soviet Union in 1941. It passed its State acceptance tests in the autumn of 1942, but was not placed into production as there was not any production capacity available, although it was tested on a number of different prototypes during the war. The M-72 of early 1945 was a boosted version of the M-71 and was superseded by the ASh-73 before production could get underway.

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