Alekseyev I-21
The Alekseyev I-21 was a post-war Soviet jet fighter project developed under Semyon M. Alekseyev at OKB-21 in Gorky during the critical transition from piston to jet propulsion in the late 1940s. Conceived as a twin-engine, single-seat interceptor, the design reflected contemporary Soviet requirements for high speed, heavy cannon armament, and adequate range for air defence duties. Although promising in flight testing, the I-21 family, encompassing the I-211, I-215, and I-215D, was overtaken by the rapid emergence of swept-wing fighters such as the Mikoyan-Gurevich MiG-15 and the Lavochkin La-15, and never entered production.
The initial prototype, designated I-211, was designed around the Lyulka TR-2 axial-flow turbojet. Delays in engine availability forced the substitution of the less powerful Lyulka TR-1, producing roughly 13 kN of thrust per engine. The aircraft featured a straight mid-mounted laminar-flow wing, twin under-wing engine nacelles, and a conventional tricycle undercarriage. Structurally, it was an all-metal monoplane with stressed-skin construction typical of late 1940s Soviet practice. Armament provision centred on heavy cannon armament in the nose, consistent with Soviet interceptor doctrine that prioritised destructive firepower against bomber targets. Flight testing began in 1947 and demonstrated competitive performance relative to other TR-1 powered aircraft. However, testing was curtailed after a landing accident caused significant damage. More critically, the TR-1’s limited thrust and reliability constrained overall performance, limiting the aircraft’s development potential.
Recognising these deficiencies, Alekseyev’s bureau developed an improved derivative, the I-215. The damaged I-211 was rebuilt as the I-215. The principal modification was the installation of British-designed Rolls-Royce Derwent V centrifugal turbojets. These engines delivered approximately 15.6 kN of thrust, improving acceleration, climb rate, and overall reliability. The larger engines required redesigned nacelles and modest structural changes, while fuel capacity was increased to extend range. Provisions were also made for radar installation in certain projected variants, reflecting evolving all-weather interception requirements. Flight trials indicated that the I-215 offered respectable performance for a straight-wing fighter; nevertheless, by 1948 Soviet fighter doctrine had decisively shifted toward swept-wing configurations that offered superior transonic performance. In comparative evaluations, swept-wing types such as the MiG-15 demonstrated clear aerodynamic advantages, rendering further development of the I-215 strategically redundant.
A further variant, the I-215D, served primarily as a testbed for a bicycle-type undercarriage arrangement. Instead of conventional wing-root main gear, the I-215D employed tandem main units aligned along the fuselage centreline, supplemented by small outrigger wheels beneath the engine nacelles. The forward main gear could be hydraulically “kneeling,” increasing the aircraft’s angle of incidence during take-off to reduce ground run and improve lift generation. Trials demonstrated that the system was workable and offered operational benefits, particularly for aircraft with thin wings unsuitable for conventional main gear stowage. Although the I-215D itself did not progress toward production, the experience contributed to later Soviet experimentation with bicycle landing gear arrangements on larger jet aircraft.
Alekseyev I-211
Alekseyev I-215
Alekseyev I-215D
References
Gordon, Yefim, and Dmitriy Komissarov. OKB Alekseyev: A Successor to Lavochkin. Hinckley: Midland Publishing, 2005.
Gordon, Yefim, and Vladimir Rigmant. Early Soviet Jet Fighters. Hinckley: Midland Publishing, 2002.
Gunston, Bill. The Osprey Encyclopedia of Russian Aircraft 1875–1995. London: Osprey Aerospace, 1995.
Green, William, and Gordon Swanborough. The Complete Book of Fighters. London: Salamander Books, 1994.
Primary Sources
Alekseyev, S. M. OKB-21 design bureau technical reports and prototype flight test documentation, 1947–1948. Russian State Archive of the Economy (RGAE), Moscow.
Central Aero-Hydrodynamic Institute (TsAGI). Wind-tunnel evaluation reports on I-211/I-215 configurations, 1946–1948.
Soviet Air Force Scientific Research Institute (NII VVS). State acceptance and performance trial reports for I-211 and I-215 prototypes, 1947–1948.