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Tupolev ANT-21 / MI-3


Designed at the KOSOS (Konstruktorski otdel opytnovo samolyetostroeniya, or Design Department for Experimental Aircraft Construction) within TsAGI by a brigade headed by Aleksandr A Arkhangel'sky, the ANT-21 MI (mnogomestnyi istrebitel - multi-seat fighter) was, by international standards of its day, very much state-of-the-art. Featuring all-metal stressed-skin semi-monocoque construction with partial flush-riveting and a retractable main undercarriage, the ANT-21, which was assigned the service designation MI-3, was powered by two M-17B (BMW VI) 12-cylinder water-cooled engines of 680hp. Proposed armament consisted of one 12.7mm machine gun or 20mm cannon on a pivoted nose mounting, two 7.62mm guns firing from a dorsal position and a single 7.62mm gun firing from a ventral tunnel. Three crew members were carried.

Work on the ANT-21 began on 18 January 1932, first flight taking place in August 1933. On 14 September, the starboard rudder suffered damage and separated as a result of violent flutter in a shallow dive. Arkhangel'sky elected to undertake major redesign as the ANT-21bis.


Retaining the wings, engines and undercarriage of the ANT-21, the ANT-21bis alias MI-3D (the suffix letter indicating dubler, or, literally, "understudy") mated these elements with an entirely new fuselage, which provided enclosed cockpits for all crew members, and a single fin-and-rudder. Completed in April 1934, the ANT-21bis had provision for the same armament as that of the ANT-21, but the ventral tunnel was omitted, the gun being fired instead through a trap. During initial flight trials some tail oscillation at certain power settings led to the introduction of tailplane bracing struts. State acceptance trials were conducted between July and December 1934, but the results were somewhat academic as there was little official interest in an M-17B-powered aircraft which had, in any case, been largely overtaken by the ANT-29. Consequently, further work on the ANT-21bis was discontined.

ANT-21 / MI-3
Engines: two M-17B (BMW VI) 12-cylinder, 680hp
Max take-off weight: 5500 kg / 12125 lb
Empty weight: 3670 kg / 8091 lb
Wingspan: 20.76 m / 68 ft 1 in
Length: 11.70 m / 38 ft 5 in
Wing area: 55.10 sq.m / 593.09 sq ft
Max. speed: 359 km/h / 223 mph
Range: 1120 km / 696 miles

ANT-21bis / MI-3D
Engines: two M-17B (BMW VI) 12-cylinder, 680hp
Max take-off weight: 5260 kg / 11596 lb
Empty weight: 3800 kg / 8378 lb
Wingspan: 20.76 m / 68 ft 1 in
Length: 12.30 m / 40 ft 4 in
Wing area: 55.10 sq.m / 593.09 sq ft
Max. speed: 356 km/h / 221 mph

Tupolev ANT-21 (MI-3)

Tupolev ANT-21bis (MI-3D)



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