MiG-25

The Mikoyan-Gurevich MiG-25 (russian: Микоян и Гуревич МиГ-25; NATO reporting name: Foxbat) is a supersonic interceptor and reconnaissance aircraft that is among the fastest military aircraft to enter service. Designed by the Soviet Union's Mikoyan-Gurevich bureau, it is an aircraft built primarily using stainless steel. It was to be the last plane designed by Mikhail Gurevich, before his retirement.

The first prototype flew in 1964 and the aircraft entered service in 1970. It has an operational top speed of Mach 2.83. Although its thrust was sufficient to reach Mach 3.2+, its speed was limited to prevent engines from overheating at higher air speeds and possibly damaging them beyond repair."Intelligence: Big-Mouth Belenko"
''Time'', 11 October 1976. Retrieved: 12 June 2021.Gunston and Spick pp. 132–133. The MiG-25 features a powerful radar and four air-to-air missiles and was theoretically capable of a ceiling of . When first seen in reconnaissance photography, the large wings suggested an enormous and highly maneuverable fighter, at a time when U.S. design theories were also evolving towards higher maneuverability due to combat performance in the Vietnam War. The appearance of the MiG-25 sparked serious concern in the West and prompted dramatic increases in performance for the McDonnell Douglas F-15 Eagle, then under development in the late 1960s. The capabilities of the MiG-25 were better understood by the West in 1976 when Soviet pilot Viktor Belenko defected in a MiG-25 to the United States via Japan. It turned out that the aircraft's weight necessitated its large wings.

Production of the MiG-25 series ended in 1984 after completion of 1,186 aircraft. A symbol of the Cold War, the MiG-25 flew with Soviet allies and former Soviet republics, remaining in limited service in several export customers. It is one of the highest-flying military aircraft, one of the fastest serially produced interceptor aircraft, and the second-fastest serially produced aircraft after the SR-71 reconnaissance aircraft, which was built in very small series compared to the MiG-25."Global Aircraft – Top 50 Fastest Aircraft."
''The Global Aircraft Organization,'' 24 April 2007. Retrieved: 30 June 2011. , the MiG-25 remains the fastest manned serially produced aircraft in operational use and the fastest plane that was offered for supersonic flights and edge-of-space flights to civilian customers.

Design and development

Background

During the Cold War, Soviet Air Defence Forces, PVO (not to be confused with Soviet Air Force, VVS) was given the task of strategic air defence of the USSR. This meant not only dealing with accidental border violations, but more importantly defending the vast airspace of the USSR against US reconnaissance aircraft and strategic bombers carrying free-fall nuclear bombs. The performance of these types of aircraft was steadily improved. In the late 1950s, the very high altitude overflights of Soviet territory by the Lockheed U-2 revealed the need for a higher altitude interceptor aircraft than available at that time.

The subsonic Boeing B-47 Stratojet and Boeing B-52 Stratofortress strategic bombers were followed by the Mach 2 Convair B-58 Hustler, with the Mach 3 North American B-70 Valkyrie on the drawing board at that time. A major upgrade in the PVO defence system was required, and, at the start of 1958, a requirement was issued for manned interceptors capable of reaching and heights of up to . Mikoyan and Sukhoi responded.

The Mikoyan-Gurevich OKB had been working on a series of interceptors during the second half of the 1950s: the I-1, I-3U, I-7U, I-75, Ye-150, Ye-150A, Ye-152, Ye-152A, Ye-152P, and Ye-152M. The Ye-150 was noteworthy because it was built specifically to test the Tumansky R-15 engine, two of which would later be used for the MiG-25. This led to Ye-152, alternatively known as Ye-166, which set several world records. The Ye-152M (converted from one of the two Ye-152 aircraft) was intended to be the definite heavy interceptor design. But before it was finished, the PVO had selected the Tupolev Tu-128. As the work on the MiG-25 was well under way, the single-engine Ye-152M was abandoned.

Development

Work on the new Soviet interceptor that became the MiG-25 started in mid-1959, a year before Soviet intelligence learned of the American Mach 3 A-12 reconnaissance aircraft.Spick 2000 It is not clear if the design was influenced by the American A-5 Vigilante.

The design bureau studied several possible layouts for the new aircraft. One had the engines located side by side, as on the MiG-19. The second had a stepped arrangement with one engine amidships, with exhaust under the fuselage, and another in the aft fuselage. The third project had an engine arrangement similar to that of the English Electric Lightning, with two engines stacked vertically. Options two and three were both rejected because the size of the engines meant that either of them would result in a very tall aircraft, which would complicate maintenance.

The idea of placing the engines in underwing nacelles was also rejected because of the dangers of any thrust asymmetry during flight. Having decided on engine configuration, there was thought of giving the machine variable-sweep wings and a second crew member, a navigator. Variable geometry would improve maneuverability at subsonic speed, but at the cost of decreased fuel tank capacity. Because the reconnaissance aircraft would operate at high speed and high altitude, the idea was soon dropped. Another interesting but impractical idea was to improve the field performance using two RD36-35 lift-jets. Vertical takeoff and landing would allow for use of damaged runways during wartime and was studied on both sides of the Iron Curtain. The perennial problem with engines dedicated to vertical lift is they become mere dead weight in horizontal flight and also occupy space in the airframe needed for fuel. The MiG interceptor would need all the fuel it could get, so the idea was abandoned.

The first prototype was a reconnaissance variant, designated Ye-155-R1, that made its first flight on 6 March 1964.Belyakov and Marmain 1994, p. 398. It had some characteristics that were unique to that prototype, and some of these were visually very evident: the wings had fixed wingtip tanks with a capacity, to which small winglets were attached for stability purposes, but when it was found that fuel sloshing around in the tanks caused vibrations, they were eliminated. The aircraft also had attachments for movable foreplanes, canards, to help with pitch control at high speed (provisions for canards had previously been installed, but not used, on the Ye-152P).Lake 1998, p. 108.Belyakov and Marmain 1994, pp. 272–274.

The first flight of the interceptor prototype, Ye-155-P1, took place on 9 September 1964.Belyakov and Marmain 1994, p. 391. Development of the MiG-25, which represented a major step forward in Soviet aerodynamics, engineering and metallurgy, took several more years to complete.Belyakov and Marmain 1994, pp. 387–388.

On 9 July 1967, the new aircraft was first shown to the public at the Domodedovo air show, with four prototypes (three fighters and a reconnaissance aircraft) making a flypast.Lake 1998, p. 109.

Aviation records

The Mikoyan-Gurevich design bureau soon realized that the performance of the new aircraft gave it great potential to set new flight records. In addition to their normal duties, the prototypes Ye-155-P1, Ye-155-R1, Ye-155-R3 were made lighter by removing some unneeded equipment and were used for these attempts. Under Federation Aeronautique Internationale (FAI) classification, the Ye-155 type belonged to class C1 (III), which specifies jet-powered land planes with unlimited maximum take-off weight. Records set included:
* The first claim was for world speed records with no payload and payloads of . MiG OKB Chief Test Pilot Aleksandr Vasilyevich Fedotov reached an average speed of over a circuit on 16 March 1965.
* For pure speed, with no payload, test pilot Mikhail M. Komarov averaged over a closed circuit on 5 October 1967. On the same day, Fedotov reached an altitude of with a payload. The MiG eventually became the first aircraft to go higher than .
* Time to height records were recorded on 4 June 1973 when Boris A. Orlov climbed to in 2 min 49.8 s. The same day, Pyotr M. Ostapenko reached in 3 min 12.6 s and in 4 min 3.86 s.
* On 25 July 1973, Fedotov reached with payload and with no load (an absolute world record).Belyakov and Marmain 1994, p. 392. In the thin air, the engines flamed out, and the aircraft coasted in a ballistic trajectory by inertia alone. At the apex the speed had dropped to .
* On 31 August 1977, Ye-266M again flown by Fedotov, set the recognized absolute altitude record for a jet aircraft under its own power.Belyakov and Marmain 1994, pp. 406–407. He reached at Podmoskovnoye, USSR in zoom climb (the absolute altitude record is different from the record for sustained altitude in horizontal flight). The aircraft was actually a MiG-25RB re-engined with the powerful R15BF2-300. It had earlier been part of the program to improve the aircraft's top speed that resulted in the MiG-25M prototype.

In all, 29 records were claimed, of which seven were all-time world records for time to height, altitudes of and higher, and speed. Several records still stand.

Technical description

Because of the thermal stresses incurred in flight above Mach 2, the Mikoyan-Gurevich OKB had difficulties choosing what materials to use for the aircraft. They had to use E-2 heat-resistant Plexiglas for the canopy and high-strength stainless steel for the wings and fuselage. Using titanium rather than steel would have been ideal, but it was expensive and difficult to work with. The problem of cracks in welded titanium structures with thin walls could not be solved, so the heavier nickel steel was used instead. It cost far less than titanium and allowed for welding, along with heat-resistant seals.Gordon 2008 The MiG-25 was constructed from 80% nickel-steel alloy, 11% aluminium, and 9% titanium.Eden 2004, p. 308. The steel components were formed by a combination of spot welding, automatic machine welding, and hand arc welding methods.

Initially, the interceptor version was equipped with the TL-25 ''Smerch-A'' (also referred to as ''Product 720'') radar, a development of the system carried by the earlier Tu-128. While powerful and thus long-ranged and resistant to jamming, the system—due to the age of its design and its intended purpose (tracking and targeting high- and fast-flying US bombers and reconnaissance aircraft)—lacked look-down/shoot-down capability, which limited its effectiveness against low-flying targets. (This is one of the reasons why it was replaced with the Mikoyan-Gurevich MiG-31, whose Zaslon radar has that capability.) By the time the MiG-25 entered service in 1969, this was a serious shortcoming, as strategic bombing doctrine was shifting towards low-level penetration of enemy territory. After Belenko's defection to Japan exposed this flaw to the West, a government decree issued on 4 November 1976 called for urgent development of a more advanced radar. This resulted in the pulse-Doppler radar ''Sapphire-25'' system fitted to the MiG-25PD variant.

As an interceptor, typical armament includes four R-40 long-range air-to-air missiles, each fitted with either an infrared seeker (R-40T/TD) or a semi-active radar homing seeker (R-40R/RD) and a maximum range of against a high-flying target on a collision course. A fuel tank could be suspended under the fuselage. The aircraft could carry unguided gravity bombs to fulfill a rudimentary strike role. As the bombs would weigh no more and incur no more drag than its regular load of R-40 missiles, its performance was not impaired, leading to some impressive bombing feats; when released at an altitude of and a speed above Mach 2, a bomb would have a range of several tens of kilometres.

The MiG-25 was theoretically capable of a maximum speed exceeding Mach 3 and a ceiling of . Its high speed was problematic: although sufficient thrust was available to reach Mach 3.2, a limit of Mach 2.83 had to be imposed as the engines tended to overspeed and overheat at higher air speeds, possibly damaging them beyond repair.

The design cruising speed is Mach 2.35 (2,500 km/h) with partial afterburner in operation. The maximum speed of Mach 2.83 (3,000 km/h) is allowed to maintain no more than 5 minutes due to the danger of overheating of the airframe and fuel in the tanks. When the airframe temperature reaches , the warning lamp lights up, and the pilot must reduce airspeed. The use of a partial afterburner and a cruising flight altitude makes it possible to have a range only less than when flying Mach 0.9 at altitudes . The maximum altitude of flight without an afterburner in operation is . The poor fuel consumption in the subsonic regime, and hence range, is due to the engines having extremely low pressure ratio of just 4.75 at subsonic speeds. The specific fuel consumption (SFC) of the engines is 1.12lb/(h·lbf) in cruise and 2.45lb/(h·lbf) with afterburners. For comparison purposes, this is 50% worse in cruise than the first generation of F100 engines from the F-15 Eagle, but the SFC with afterburners is actually nearly equal, despite the F100 being a far newer engine design.

Production

Full-scale production of the ''MiG-25R'' ("Foxbat-B") began in 1969 at the Gorkii aircraft factory (Plant No. 21). The ''MiG-25P'' ("Foxbat-A") followed in 1971, and 460 of this variant were built until production ended in 1982. The improved PD variant that replaced it was built from 1978 till 1984, with 104 aircraft completed. Subsequently the Gorkii factory switched over production to the new MiG-31.

Western intelligence and the MiG-25

Inaccurate intelligence analysis caused the West initially to believe the MiG-25 was an agile air-combat fighter rather than an interceptor. In response, the United States started a new program, which resulted in the McDonnell Douglas F-15 Eagle. NATO obtained a better understanding of the MiG-25's capabilities on 6 September 1976, when a Soviet Air Defence Forces pilot, Lt. Viktor Belenko, defected, landing his MiG-25P at Hakodate Airport

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