Complex sentence: Yermolaev became the chief of OKB of R.L.Bartini in 1939 after Bartini was arrested; he led the development and production of Stal-7 based long range bomber Er-2 (DB-240) and its variants Er-4 with ACh-30 engines.
Split into simpler sentences: Yermolaev became the chief of OKB of R.L.Bartini in 1939 after Bartini was arrested. He have lead the development and production of Stal-7 based long range bomber Er-2 (DB-240) and its variants Er-4 with ACh-30 engines.