Tairov designed and built the OKO-6 to a Soviet Air Force requirement for a twin-engined escort fighter to escort and protect bombers on long range missions. Competing proposals included the GrushinGr-1, MiG DIS and Polikarpov TIS. The aircraft was a single-seat monoplane of mixed construction; with wing spars of 30KhGSA steel, D1 aluminium alloy ribs, flush riveted skin, and elektronmagnesium alloyleading edges; the fuselage was largely of flush-riveted D1 aluminium alloy built as a semi-monocoque shell with a wooden tail section. Armour was provided fore and aft of the compact cockpit, and the heavy armament was grouped around the nose of the aircraft, with two 12.7mm BSmachine guns in the upper nose and four ShVAK20 cannon in the lower forward fuselage. The engines were housed in large underwing nacelles and drove counter rotating propellers to eliminate torque effect with throttle movement. First flown by Yu. K. Stankevich on 31 December 1939, the first aircraft was also tested by LII until the summer of 1940 when one of the engines threw a connecting-rod. The directional stability was found to be unsatisfactory so the second prototype was built with a much longer rear fuselage, twin fins on the tips of a longer span tailplane as well as more powerful engines with LH rotation. The third prototype was initially called OKO-6bis, changed to Ta-3, was flown by Stankevich in May 1941 with M-89 engines, one AM-37 37mm cannon and two ShVAK20 20mm cannon The fourth airframe which was to be the Ta-3bis with M-82 engines was abandoned due to the German invasion, and further work on the Ta-3 was halted when Tairov was killed in an airline crash, traveling between Moscow and Kuybyshev, in December 1941.
Variants
OKO-6 – initial prototype with 950/1000 hp M-88 engines, short fuselage and single fin and rudder. Armament:-2 x 12.7mm BS machine-guns and 4 x 20mm ShVAK-20 cannon in the forward fuselage.
OKO-6bis – second prototype with lengthened fuselage, twin fins and M-88R engines. Armament:- 2 x 7.62mm ShKAS machine-guns and 4 x 20mm ShVAK-20 cannon in the forward fuselage.
Ta-3 – third prototype renamed from OKO-6bis, with M-89 engines and increased span wings. Armament:- 1x 37mm AM-37 cannon and 2 x 20mm ShVAK-20 cannon in the forward fuselage.
Ta-3bis – uncompleted fourth prototype, with 1,250 hp Shvetsov M-82 engines, abandoned with the German invasion of Ukraine. Armament:- 1x 37mm AM-37 cannon and 2 x 20mm ShVAK-20 cannon in the forward fuselage.
