MiG-21I – The Delta Wing Fishbed
The Mikoyan-Gurevich MiG-21 ‘Fishbed’ is one of the most successful combat aircraft ever made, and is the most-produced supersonic fighter in aviation history. There are a staggering variety of sub-models and variants, and these versions performed a large number of different mission profiles and tasks, including that of testing experimental components for other aircraft concepts. Such is the story of one rare variant of the Fishbed, the MiG-21I which was also known as the ‘Analog’.
These two aircraft were constructed to test the wing design of one of the most problematic high-performance aircraft ever made, the Tupolev Tu-144 supersonic passenger jet.
The MiG-21I was a specialised tailless version of the Fishbed and was constructed with a double-delta wing similar to the SAAB Draken, and this wing configuration was envisaged to be suitable for the supersonic passenger aircraft project known as the Tu-144.
The first test MiG-21I performed over 140 flights to prove the wing concept and completed the entire test program without any problems, but this success wasn’t able to be transferred to the Tu-144, which was a dismal failure as both a passenger aircraft and technology demonstrator.
Design and Development
During almost the entirety of the Cold War, the Soviet Union was always portrayed as a dynamic and progressive nation with cutting-edge technological capabilities in many fields, though the truth was markedly different from this propagandised image.
Nowhere was this more apparent than in the field of commercial and military aviation, where vast sums of money were expended by the Soviet government to compete with the latest Western concepts and designs.
All of the military designs had obvious combat applications, and the appropriate secrecy in the development of these aircraft was exercised, but the story was far different for commercial design concepts.
In these cases, it was the national prestige that would be enhanced by a Soviet design for a commercial aircraft that was found to be superior to any in the West, but this was seldom achieved.
As such, these aircraft designs were showcased to one and all, with the intended effect of promoting the superiority of the communist style of the political system.
Soviet Military Intelligence (GRU) snooping into Western commercial aviation projects led to the careful monitoring of the Anglo-French Concorde supersonic passenger aircraft program, and the Soviet government started conceptualising a similar project as early as 1962.
In July 1963 this program was formalised as the TU-144 supersonic airliner, and with several new technologies for this new aircraft needing to be tested on other airframes this is where the MiG-21I enters the story.
The Mikoyan factory was tasked with building two specialised airframes to test wing designs, and the company used the base MiG-21 design as a template. Construction of these two aircraft was undertaken in the latter part of 1967, and was completed by March 1968.
In April 1968 the first flight was performed by Mikoyan-Gurevich test pilot O.V. Gudkov.
The MiG-21I was one of the most unusual variants of the Fishbed, but despite its tailless design (unlike the conventional base Fishbed airframe) the aircraft still employed many of the components found in production models of the MiG-21serving in Warsaw Pact countries.
This included the power plant, the cockpit and other systems like the undercarriage and other fuselage components.
As the MiG-21I was an extremely specialised test aircraft, there was no requirement for the equipment to carry and employ weapons to be fitted, along with only needing a reduced avionics fit as well.
This had the effect of reducing the overall weight of the test airframes, and as such the prototypes returned some impressive performance figures.
All tailless aircraft are controlled in flight by a rudder, and a specialised horizontal flight control surface known as an elevon. The elevon is utilised in tailless aircraft designs to replace both the elevator and aileron flight control surfaces and control both pitch and roll during controlled flight.
In the MiG-21I, the normal tailplanes with elevators were removed, and the double-delta wing was extended to the rear of the fuselage, in line with the vertical tailplane and rudder.
The wing leading edge (or Leading Edge Root Extension or LERX) was constructed with a sweep-back angle of 78 degrees and test cameras were fitted in streamlined pods in two locations; just behind the cockpit, and on top of the vertical tailplane.
One unique feature of these airframes was a mechanism for transferring weight to the front or rear of the airframe to change the centre of balance, using a hydraulic system pumping an inert fluid with a mass of nearly 300 kilograms.
This modification was needed to help test the elevons at different speeds and angles of attack.
The flight test program of the first MiG-21I prototype lasted approximately eighteen months and concluded in December 1969, and 140 flights were undertaken by both Mikoyan test pilots and some military aviators as well.
All these flights were successful and the double-delta wing design for the Tu-144 was proved as an operational concept, but the aircraft was unfortunately destroyed after one of the test pilots attempted to perform aerobatics in the aircraft, resulting in the loss of the airframe and the death of the unfortunate pilot.
As the test program had been mostly completed, the second prototype was used to train pilots for flying the Tu-144, as the flight characteristics were similar (in regards to lift/stall wing characteristics) for both aircraft.
It also spent some time at the Gromov Flight Research Institute for a series of test flights exploring supersonic flight profiles. After both these tasks were completed, the remaining MiG-21I prototype was handed over to the Morino Air Force Museum.
The MiG-21I shared many dimensions and specifications with the base Fishbed model but was considerably lighter as the result of not carrying any armament, and only fitted with the basic avionics needed for test flights.
As such, the MiG-21I had some sparkling performance figures and had no problems testing the TU-144 wing design under supersonic flight conditions.
The MiG-21I had a height of 4.71 metres (15 feet 4.5 inches), a length of 12.3 metres (40 feet 3 inches) and a wingspan of 11.5 metres (37 feet). Empty, the airframe tipped the scales at 5,460 kilograms (12,037 pounds), and the gross loaded mass of the aircraft was 8,750 kilograms (19,290 pounds).
Both test aircraft was powered with a single R-13F300 augmented turbojet, and this produced dry thrust figures of 4,070 kg/f, and when in afterburner generated 6,490 kilograms of thrust.
This gave the MiG-21I some impressive performance figures; a top speed at an altitude of 2,100 km/h or Mach 2.06, and the aircraft could attain a blistering 1,200 km/h on the deck.
The MiG-21I had a service ceiling of 20,000 metres, but this was rarely approached during the flight test program.
The Fishbed was a wonderful design for a supersonic fighter, and like most things this magnificent aircraft attempted it was a great success in nearly all roles and configurations, and this included the unglamorous and often-dangerous task of flight testing components for other aircraft designs and concepts.
The MiG-21I successfully validated the proposed wing design for the Tu-144 and can be said to have performed this task with aplomb, and it was no fault of the test aircraft that the Tu-144 turned out to be such a gigantic lemon – and embarrassment.
The Tu-144 only flew commercially 103 times, and only 55 of these flights had to pay passengers.
Maybe this can be partially explained by an early flight in January 1978; most of the aircraft systems failed before take-off and during the flight, but due to foreign journalists covering the trip it was decided to proceed anyway to stop national embarrassment should the flight be cancelled.
Perhaps they should have cancelled; an alarm siren went off just after take-off and couldn’t be turned off, and crew and passengers had to endure the civil-defence level of volume for the entire 75-minute flight. It was rumoured that many of the deplaning passengers became very fond of rail travel.
None of this can be blamed on the MiG-21I, which performed the flight testing of the Tu-144’s proposed wing design flawlessly and enabled the larger aircraft to take to the air, but guilt-by-association works in the aviation sphere as well, and the MiG-21I will always be associated with the disaster that was the Tu-144, regardless of its own competence and ability in completing all its design objectives and helping the Tu-144 project towards completion.
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