sentences:  The first prototype made its maiden flight in June 1948 from Medvyezhe Ozero, near Omsk.Official testing resulted in a number of changes to the design, with a large dorsal fin being fitted, and spoilers being added to reduce landing runs, while the payload of the glider was increased to allow an ASU-57 assault gun to be carried.As such the Yak-14 passed its acceptance trials from August to September 1949, with the glider entering mass production later that year.