sentences:  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, itself starting its development in 1937