The MiG 21I was an experimental version developed from MiG-21S. Only two was produced. They were also called MiG-21I Imitator and MiG-21I Analog. Both aircraft were taken from the assembly line of the MiG-21S, but were powered by a later engine, the R-13-300, rated at 6,490kg (14,308 Ib). This engine could provide a large airflow for blown flaps, but as the Tu-144 (and thus the 2I-11) was a tailless delta no such flaps could be fitted.
The wing was totally new, being of an ogival shape with the root chord extending over almost the entire length of the fuselage. The quite sharp leading edge had the remarkable sweep angle of 78°, before curving out to a sweep angle of 55° over the outer wings. There was no droop (downward camber) along the leading edge. On the trailing edge of each wing were four fully powered surfaces, the inner pair being plain flaps and the outer pair elevens (surfaces acting as both elevators and ailerons). The wing was incredibly thin, thickness/chord ratio being only 2.3 per cent inboard and 2.5 at the tip. Thus, the control-surface power units were faired in underneath, the outer fairings extending over the entire chord of the wing. The wing leading edge was made detachable so that different shapes could be tested.
Among other modifications was an increase in fuel capacity to 3,270 litres (719 Imperial gallons), and of course there was no provision for armament. Partly because of a ‘chicken and egg’ situation, in which Mikoyan was uncertain precisely what shape to make the wing, whilst the purpose of the Analog was to teach Tupolev how to design the Tu-144’s wing, the programme ran at least a year too late to assist the design of the SST. Eventually pilot Gudkov flew 23-11/1 on 18th April 1968, with civil registration SSSR-1966, the intended first-flight year. The Tu-144 pilots flew this aircraft before first flying the 44-00 (first Tu-144) on 31st December 1968, with the 23-11/1 accompanying it as chase aircraft. The 23-11/2 differed mainly in that all eight wing movable surfaces were elevens. It was first flown by Volk in late 1969.
Most of the second aircraft’s flying was done with a large LERX (leading-edge root extension) giving increased area from the new curved front portion. The 2I-11/2 carried out extensive aerodynamic and control research before going to the WS Museum at Monino. The 2I-11/1 was crashed on 28th July 1970. Mikoyan did not act on the suggestion of the main 23-11 test pilots that he should develop a fighter version.