The Alekseyev I-21 was a Soviet twin-engined jet fighter, built in the late 1940s. Two prototypes were constructed with the designation of I-211, of which one was converted into the I-215 with more powerful engines. A third aircraft was built to evaluate the bicycle landing gear arrangement for use in other aircraft. The fighter was not accepted for production as it was inferior to the swept-wing fighters like the Mikoyan-Gurevich MiG-15. Development After working as Lavochkin's right-hand man during World War II, Semyon Alekseyev was appointed as Chief Designer of OKB-21 (design bureau) at Gor'kiy. The Council of the People's Commissars directed Alekseyev and other designers to develop jet fighters using more powerful engines than the captured German Jumo 004 and the BMW 003 and their Soviet-built copies. The result of Alekseyev's efforts was the I-21 (Russian: istrebitel (fighter)), which was planned to be produced in several variants. The I-21 was a twin-engined, all-metal, single-seat jet fighter, with straight laminar flow wings, mid-set on a circular fuselage. The fighter's Lyul'ka TR-2 turbojet engines were mounted below the wings much like those on the German Messerschmitt Me 262 fighter. Underneath the engine nacelles were hardpoints that could carry bombs or drop tanks. The slightly swept tail unit was cruciform in layout with the tailplane set at approximately half-fin span with slight dihedral. The aircraft's structure was generally constructed from high-strength B-95 duralumin, although high-strength steel and "Elektron" magnesium alloy were used for some components. A hydraulically retractable tricycle undercarriage was fitted, using twin wheels for the nose and main landing gear. Hydraulically actuated airbrakes were fitted either side of the rear fuselage. Alekseyev initially planned to arm the aircraft with three Nudelman N-37 autocannon, each with 30 rounds, but later decided upon a pair of Nudelman-Suranov NS-23 autocannon with 75 rounds per gun. Design work on the I-210 (I-21 version 0) was concurrent with the I-21, probably as a fall back for any lack of availability of the latter's TR-2 engines. The only significant difference was the substitution of BMW 003 engines (or the reverse-engineered RD-20), but the ex-German engine's significantly inferior thrust rating meant that it would never meet the I-21's speed requirement. Even replacing the BMW 003 with the slightly more powerful () Jumo 004 would not allow the I-210 to meet the speed requirement and the project was cancelled before any metal was cut. Construction of the first