The Che-2/MDR-6 - NATO reporting name 'Mud' - was a Twin-engined (M-63) flying boat, first flown in 1937 and used until the 1950's. The Che-2 (which was named MDR-6 until 1941) had a high-set, slightly gulled wing, with stabilising floats on the wingtips, that were retractable on some models. Later models had Klimov M-105 engines and even M-107 engines. It was a successful competitor of the Beriev MDR-5. 

Grateful thanks goes to Evgeny Polovinnik for sharing these outstanding plans with us. Thanks, Evgeny.