Tupolev ANT-21

ANT-21
Role	Fighter
National origin	Soviet Union
Manufacturer	Tupolev
First flight	1933
Number built	2
Developed from	Tupolev ANT-7

The Tupolev ANT-21 was a Soviet twin-engined four-seat heavy fighter, which also had the designation MI-3 (Mnogomestnyi Istrebitel – Multi-seat fighter). It was not accepted for production, only two prototypes being built.

In January 1938, the Soviet Air Forces ordered the TsAGI design bureau led by Andrei Tupolev to design a twin-engined multi-seat fighter to replace the KR-6 escort fighter version of the Tupolev ANT-7 twin-engined multi-purpose aircraft. Tupolev assigned design of the new fighter to a team led by Alexander Arkhangelsky. This was Arkhangelsky's first project as lead designer. The resulting aircraft, the ANT-21, was like the ANT-7, a monoplane, with its corrugated all-metal wings based on those of the ANT-7, but having reduced span, and with the corrugations covered in fabric to reduce drag. The oval-section fuselage was a new design, being a partially flush riveted semi-monocoque structure made of duralumin, a first for Tupolev aircraft, while it was fitted with a twin-tail. It also had a retractable tailwheel undercarriage, novel for the time.

The aircraft's pilot sat in an open cockpit above the leading edge of the wing, with one gunner sitting in the nose operating two machine guns, a second gunner in a dorsal position with two more machine guns, while another crewman operated a ventral gun firing through a hatch. Two fixed machine guns could be operated by the pilot. Two Mikulin M-17 engines powered the ANT-21, as used by the ANT-7.

The first prototype, officially designated MI-3 and nicknamed Mitrich made its maiden flight in August 1933. Initial testing was successful, the ANT-21 being popular with its test pilots, but when being dived at nearly 400 km/h (250 mph), severe flutter was encountered in the aircraft tail, with the starboard rudder breaking off and the aircraft making a heavy landing.

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Wikipedia