The Shvetsov ASh-21 (Russian: èòõÃÂþò ÃÂè-21) is a seven-cylinder single-row air-cooled radial aero engine.
The ASh-21 is basically a single-row version of the Shvetsov ASh-82. The ASh-21 also incorporates a number of parts from the ASh-62 radial engine. Design began in 1945, and by 1947 testing had finished and production had begun. Between 1947 and 1955 7,636 ASh-21 engines had been built in the USSR and beginning in 1952 it was produced in Czechoslovakia as the M-21.