The MiG-31 Foxhound: One of the World's Greatest Interceptors

The Mikoyan-Gurevich MiG-31 'Foxhound' is one of the most powerful and effective interceptors flying today. It owes its oustanding capability to an effective combination of performance, weaponry, and avionics. Even though it first flew more than 30 years ago, it is still Russia's most effective air defence interceptor and forms the backbone of its air defence force and will continue to do so well into the 21st century.

The mighty MiG-31 Foxhound A MiG-31E landing (RSK MiG)

The Aircraft


In the late 1960s the Soviet government began looking for a new long-range, extended endurance interceptor to replace its Tupolev Tu-28s and MiG-25 Foxbats. The new interceptor was intended to counter the threat of low-flying cruise missiles launched from NATO/US B-52s and B-1s, which the MiG-25 was unable to do. MiG-25s functioned well as high-altitude interceptors with the help of ground control data links, as their original mission was to intercept the USAF's high-altitude Mach 3 B-70 Valkyrie bomber. However, the B-70 never went into production on account of defence cutbacks. The Foxbat's avionics and performance were largely ineffective against low-flying targets and so a more capable aircraft was needed.

From the late 1960s, NATO bombers and attack aircraft had changed tactics and were flying ever lower attack profiles intended to avoid the growing threat of surface-to-air missiles (SAMs). Newly introduced cruise missiles were also flying low and fast, proving difficult to intercept. The MiG-25 was unable to fly at supersonic speeds at low level, which was a serious disadvantage in intercepting enemy aircraft and missiles. The Soviets needed a replacement that was supersonic at all altitudes and able to attack low-flying and multiple small targets. In order to do this, far more efficient engines and completely new avionics were required, together with a dedicated rear crewmember to manage them.

Development of the new aircraft, designated MiG-31, began in 1967 and on 24 May 1968 the Soviet government ordered production of a prototype, designated Ye-155MP. The Mikoyan Design Bureau originally considered a number of different configurations for the new aircraft. These included the Ye-155M variable geometry two seater powered by two RD36-41M turbojets, the Ye-158 tailless delta with canards, and a two-seat MiG-25 with a new wing, elements of which were developed into the MiG-31. The MiG-31 was to carry the Zaslon phased array radar capable of detecting all types of aerial targets flying at long ranges and varying altitudes, making the MiG-31 independent from ground control. Under normal circumstances the rear radar operator would guide the pilot to the target, but the MiG-31 could also be guided by ground control using a digital datalink.

Detailed design work on the MiG-31 began in 1969 when the basic Ye-155MP design was modified, giving it a lighter structural weigh, an improved climb rate and higher service ceiling. The Ye-155MP was actually a heavily modified MiG-25MP, and looked like a stretched Foxbat with a new wing, second cockpit and underfuselage R-33 (AA-9 Amos) missile attachments, although it didn't have wing root extensions. Construction began in 1972 and in 1975 the prototype was completed at the Mikoyan Machine-building Plant in Moscow. By then the prototype had a new wing with leading edge root extensions (lerx's), leading edge slats, ailerons and flaps. However, in place of the Zaslon radar and infrared sensor were weights intended to simulate these advanced avionics.

The Ye-155MP (serial 831) made its maiden flight on 16 September 1975 with chief test pilot Alexsandr Fedotov at the controls. The second prototype (serial 832) made its maiden flight the next year on 22 April 1976, again piloted by Fedotov. This aircraft had the complete avionics suite, including the Zaslon radar and infrared sensor, as well as reduced wing area and smaller underfuselage fins. (Fedotov and his crewmember were later killed in a MiG-31 crash on 4 April 1984 when the aircraft's systems failed.) Development proceeded slowly and by 1977 two pre-production aircraft (serials 011 and 012) were built by the Sokol Aviation Manufacturing Plant at Nizhny Novgorod, with 012 first flying on 30 June and 011 making its maiden flight on 13 July 1977. Compared to the first two prototypes, these aircraft had increased span flaps, revised wings, taller vertical tails and GSh-6-23 cannons, each cannon having six 23-mm barrels. In May 1977 the first round of official testing began, and ended in December 1978. After satisfactory results, which included a MiG-31 tracking no less than 10 targets simultaneously with its Zaslon radar on 15 February 1978, it was decided to begin production at Sokol in 1979.

A wide variety of aircraft were used in the MiG-31 test programme, including two Tu-104s used to test the Zaslon radar, a MiG-21 to test R-33 missile systems, and three MiG-25s to test the R-33 missiles, engines and avionics. The second stage of official testing began in September 1979 and ended exactly one year later. Production started in 1979 and about 450 Foxhounds were built, with the last production Foxhound being delivered in April 1994. Initial MiG-31 deliveries to air force units began in 1981 and by 1983 initial operational capability was achieved. By the end of the year the MiG-31 was serving with 11 regiments, replacing MiG-23s, Sukhoi Su-15s and Tu-28s in the air defence role. By 1987 over 150 MiG-31s were deployed across the Soviet Union, especially in the west and east.

There are currently around 315 MiG-31s in service with Russian air defence forces and tactical units and around 34 with Kazakhstan. These latter aircraft, flying with the 356th IAP (Istrebitel'nyi Aviatsionny Polk or Fighter Aviation Regiment) based at Semipalatinsk, were left in Kazakhstan after the Soviet Union collapsed.

China reportedly ordered 24 MiG-31s in 1992 and they were expected to be assembled at a newly set up factory in Shenyang, with production at a rate of four per month until completion of the last aircraft by 2000. It was reported that the agreement included a license to build up to 700 aircraft and it was expected that at least 200 MiG-31s would be operational by 2010. However, nothing has happened - either the contract was cancelled or it was never signed. Instead, China bought Su-27/30 Flankers (designated J-11 in China) to fulfil its long-range interceptor requirement.

The Sokol plant at Nizhny Novgorod has stated its willingness to begin production of the MiG-31 again, to meet even small orders. So far no orders have been received, even though there have been persistent reports of interest from Iran and Syria.

The first time the Western world caught wind of the MiG-31 was when the Soviet pilot Viktor Ivonovich Belenko defected to Japan. Originally based at the 513th Fighter Regiment of Soviet Air Defence Command in Siberia, he flew his MiG-25 to Hakodate in September 1976. When questioned by the US (he went to America and was allowed to live there), he described the MiG-31 as a "super Foxbat" with two seats, a strengthened fuselage and powerful look-down/shoot-down radar. However, it was not until 1978 that the aircraft was first observed. A US spy satellite viewed one of the prototype or pre-production machines flying at 6 000 metres (19 690 ft) intercepting a cruise missile-sized target drone flying at 60 metres (200 ft) altitude and 20 kilometres (12 miles) from the MiG-31. In mid 1982 NATO designated the aircraft 'Foxhound'. The West finally got a good look at the MiG-31 in 1985 when a Norwegian pilot intercepted a Foxhound over the Barents Sea and took some pictures of it. It was suspected that this might have been a staged photo opportunity designed to unveil the aircraft.

A MiG-31 Foxhound in flight


The Aircraft

Although the MiG-31 looks roughly like the MiG-25, it is a completely new and vastly more capable machine. The basic Foxbat configuration has been retained, with high-mounted sweptback wings, a rectangular and diagonally cut air intake on each side of the fuselage, twin ventral fins under the tail and backward tapered twin tail fins that are canted slightly outward. The MiG-31 has a new airframe strengthened to 5 g, as opposed to the MiG-25's 4.5 g, allowing the Foxhound to fly at supersonic speeds at low altitude - it can do an impressive Mach 1.23 (1 500 km/h or 932 mph) at sea level. While the MiG-25's airframe was constructed from 80% nickel steel, 11% aluminium and 8% titanium, the MiG-31 has a new airframe consisting of 49% arc-welded nickel steel, 33% light metal alloy, 16% titanium and 2% composites. This should have made the Foxhound a much lighter aircraft than its predecessor, but the addition of new systems ultimately resulted in the MiG-31 being considerably heavier than the MiG-25.

Pilots have said that the MiG-31 was sophisticated, fast, had a long range and could climb "like a rocket". And its lack of agility was more than adequately compensated for by its ability to engage virtually any possible target from an extremely long standoff range.

The MiG-31's wing is very different from that of its predecessor and has a new third main wing spar, which gives it significantly greater strength. The most notable difference is the new lerx's, which have a sweep angle of 70º. Both wings are swept back at 41º, have a small anhedral of 4º from the roots and have a fence mounted above each underwing stores pylon. Each wing has four-section titanium leading-edge slats that occupy the whole leading edge, two-section trailing-edge flaps and large span flaperons near the wingtips. The leading-edge slats deploy automatically at low speeds and are used for manoeuvring. The horizontal tailplanes are all-moving, while the vertical tails have inset rudders and shallow fairings forward of the base of the leading edge.

Landing gear on the MiG-31 is also completely new and is a retractable tricycle type. The rearward retracting twin nosewheel unit with mudguard retracts rearwards into the fuselage, unlike the MiG-25, which had its nosewheels further down the fuselage and retracting forwards. The main gear features two wheels on each main unit, retracting forward into an air intake trunk. Although the twin wheels are in tandem, they are staggered slightly so the rear wheel does not follow in the track of the front one, facilitating operations from snow, gravel or unprepared ground. There is a small forward-hinged airbrake under the front of each engine intake trunk forward of the main gear doors. Other landing gear equipment consists of twin cruciform braking parachutes stowed in a fairing between and above the engine exhausts.

One of the most important requirements for the MiG-31 was not increased speed, but longer range, and in order to achieve this, new and more efficient engines were needed. The Aviadvigatel D-30F6 turbofan was chosen, although surprisingly it was not a new engine - it was developed from a commercial turbofan and adapted to use high-density T6 fuel. In order to accommodate this massive engine (which is 7 040 mm [277.2 in] long and has a diameter of 1 020 mm or 40.2 in), the air intakes were enlarged and, together with the fuselage, designed to contribute lift. Even though the fuselage was redesigned to accommodate the engines, the jet nozzles extend rearwards from the tail, unlike those of the MiG-25. Apart from being more efficient, the new air intakes also feature a moving inlet ramp, a lower moving inlet lip and have auxiliary inlet doors in their roofs. Each engine produces 9 500 kg (20 945 lb) of thrust dry and 15 500 kg (34 170 lb) with afterburning.

The redesigned and lengthened fuselage was able to accommodate even more fuel than the MiG-25 - total internal fuel capacity is an incredible 19 940 litres (4 386 gallons) in seven fuselage tanks, four wing tanks and two 'wet' fin tanks. This weighs a massive 15 500 kg (34 170 lb) and to keep the centre of gravity within limits is constantly shifted around the various tanks. In addition, there is provision for two underwing fuel tanks each with a capacity of 2 500 litres (550 gallons), and there is also a semi-retractable flight refuelling probe on the port side of the front fuselage, just ahead of the cockpit.

The MiG-31 design team originally considered placing the two crewmembers side by side, but in the end a tandem seat arrangement was followed. The pilot is seated in front while the weapons systems and radar operator sits behind. Both crew sit under individual rearward-hinged canopies, although the rear cockpit has only small side windows in its metal frame and is faired into a shallow dorsal spine which extends to forward of the jet nozzles. This gives the rear crewmember a very limited view and to compensate, he is provided with a retractable periscope. The rear cockpit has a simple set of flight controls, allowing the rear crewmember to fly the aircraft in an emergency. Both crew sit on Zvezda K-36DM zero/zero ejection seats that have built-in massage pads to keep the crew comfortable on long patrol missions. In addition, the pilot's seat has a heated backrest to allow for extended periods of ground alert.

One of the keys to the MiG-31's success is its formidable array of advanced digital avionics, especially its long-range radar. The NIIP Zaslon (in full it's actually N007 S-800 SBI-16 [RP-31] Zaslon, meaning Shield, but designated Flash Dance by NATO) electronically scanned, phased array, fire control radar is the MiG-31's primary sensor. It was the first electronically scanned phased array radar to enter service and has exceptional performance, with a search range of 200 km (124 miles) in a clutter-free forward sector and 90 km (56 miles) rearwards, and can track targets at 120 km (75 miles). It was also the first Soviet radar to have true look-down/shoot-down performance. It's able to track ten targets and engage four of them simultaneously, with the targets being prioritised by the aircraft's Argon-15 digital mission computer. Also connected to the digital computer is a semi-retractable Type 8 TP infrared search and track sensor below the cockpit.

Communications fit is quite comprehensive, consisting of UHF and HF communications radios, identification friend or foe (IFF) transmitter and receiver and transponder. Most, but not all, MiG-31s appear to have APD-518 digital air-to-air datalinks - when flying in a four-aircraft group intercept formation, the lead aircraft is linked to the AK-RLDN automatic guidance network on the ground while the other three MiG-31s have datalinks to the lead aircraft, permitting a line-abreast radar sweep zone 800 to 900 km (495 to 560 miles) wide. The air-to-air datalink can be used to communicate with Antonov An-50 'Mainstay' airborne warning and control system (AWACS) aircraft. The MiG-31 is also fitted with the MB5U15K air-to-ground tactical datalink and BAN-75 command link.

Navigation avionics are comprehensive, as they were originally designed to allow the MiG-31 to patrol deep into Arctic airspace in search of threatening Western aircraft. Trial flights included such Arctic sorties, including one aircraft flying over the North Pole. Navigation avionics consist of Marshrut long-range and Tropik medium-range radio navigation systems (similar to the US Omega and Loran respectively), as well as Shoran, Loran, radio compass, radar altimeter and marker beacon receiver. Other miscellaneous avionics consist of a voice warning system, intercom and radar homing and warning system (RHAWS). Countermeasures include active electronic warfare equipment and UV-3A flares dispensers.

Unlike the MiG-25, the MiG-31 has an internal gun, the GSh-6-23M six-barrel Gatling-type 23 mm cannon, inside a fairing on the starboard side of the lower fuselage just behind the right landing gear door. It has a rate of fire of between 6 000 and 8 000 rounds per minute and is provided with just 260 linkless rounds. It appears that early Foxhounds had only two underwing pylons, but aircraft now have four pylons. The MiG-31's main weapon is the Vympel R-33 or R-33S (designated AA-9 'Amos' by NATO) long-range air-to-air missile (AAM) with a range of 120 km (75 miles). Its guidance is either by semi-active radar homing or inertial with the option of mid-course update from the launch aircraft. Four can be carried in pairs on AKU ejector pylons semi-recessed under the fuselage, similar to that of the Grumman F-14 Tomcat. Because the underside of the fuselage is flat and not dished between the engine ducts like on the MiG-25, it is much easier for the MiG-31 to carry missiles under its fuselage. All four R-33s can be launched in salvo, with each seeking out a different target simultaneously.

The MiG-31 can also carry two R-40T (designated AA-6 'Acrid' by NATO) medium-range infrared homing or inertially guided air-to-air missiles on the inner underwing pylons with a range of 50 km (31 miles). Four short-range R-60 (designated AA-8 'Aphid' by NATO) infrared homing air-to-air missiles with a range of three kilometres (1.9 miles) can be carried in pairs on the outer underwing pylons.

A diagram of the MiG-31 Foxhound



A large number of improved Foxhound derivatives were produced or proposed. The first major modification was the fitting of the semi-retractable in-flight refuelling probe. Although the Foxhound didn't originally need it, as range was considered adequate, the aircraft's impressive performance prompted field commanders to consider it for other long-range missions like escorting maritime patrol aircraft. These missions challenged the range of the Foxhound, so the refuelling probe was fitted to between 40 and 45 later-production aircraft and retrofitted to other early-production aircraft. Standard-production aircraft are designated Foxhound-A, while those with the refuelling probe are unofficially designated MiG-31DZ.

MiG-31B: This was the second production and service variant with improved Zaslon-A radar, electronic countermeasures (ECM), electronic warfare (EW) equipment, improved R-40TD and R-60 AAMs, upgraded R-33S missiles, flight refuelling probe and improved A-723 long-range navigation system compatible with Loran/Omega and Chaika ground stations. It replaced the Foxhound-A in production in late 1990. Many older MiG-31s were upgraded by the Gorky factory to this standard and were designated MiG-31BS. In July 2000 an agreement was reached between the MiG company and the Russian Air Force for upgrading half of the Air Force's 280 MiG-31s. It's not clear to which standard they will be upgraded: either MiG-31B standard or the superior MiG-31BM standard.

MiG-31E: This designation is given to the export version of the Foxhound-A, of which the one and only prototype (serial 903) was first seen in 1997. The aircraft has downgraded systems, no active jammer, downgraded IFF and radar. It was offered to India, China and other countries and is presumably the version the Chinese almost bought in 1992. The variant was later cancelled.

MiG-31Eh: Designated Eh for Ehksport (export), this variant was proposed to China in 2000 and announced at the Zhuhai Air Show on 6 November 2000. It appears to have been rejected.

MiG-31F: This is a projected multi-role interceptor and fighter-bomber that would be able to carry a variety of TV- radar- and laser-guided air-to-surface missiles (ASMs). It would also have a variety of other changes.

MiG-31BM: The MiG-31BM designation was applied to a proposed defence suppression and ground attack variant based on the MiG-31F. Work on the aircraft was begun in 1997 and in August 1998 a demonstrator was shown with R-33S missiles under its fuselage and R-77, Kh-58 and Kh-31P missiles under its wings1. The MiG-31BM designation is now applied to the single-role interceptor upgrade to be applied to the MiG-31Bs in service. The MiG-31BM has replaced the original MiG-31M upgrade originally offered. The aircraft is able to carry R-37M and R-77M air-to-air missiles2, has upgraded radar, a satellite navigation system and new cockpit displays. MiG-31Fs, FEs and BMs will all have an upgraded radar incorporating technology developed for the MiG-31's Zaslon-M. This will give a detection capability against ultra high-speed targets travelling at more than Mach 6, will give longer range, better resolution and new synthetic aperture and real-beam mapping modes for the air-to-ground role. The new cockpit displays consist of a head-up display (HUD), pilot's tactical situation display, which is a 152 x 203 mm (6 x 8 in) colour LCD MFD, and three MFDs for the navigator. Weapons fit has been increased, with the MiG-31BM (and presumably the F and FE) being able to carry R-33S, R-37 and R-77 AAMs, as well as Kh-58E and Kh-31P anti-radiation missiles (ARMs) and possibly Kh-59, Kh-29L/T and Kh-59M ASMs3. Upgraded MiG-31s may also incorporate structural changes to increase service life, but this cannot be confirmed. Two MiG-31BMs were built and a prototype was publicly demonstrated in 1999, but lack of funding has hampered further development.

MiG-31D: This was a dedicated anti-satellite model with a flat undersurface fuselage without recesses, underwing Vympel anti-satellite missiles and no gun. The MiG-31D was also fitted with large triangular winglets above and below the wingtips to provide stability for missile launches at high altitudes. Two prototypes with ballast instead of radar in their noses were built in 1986 and flight-tested in 1987, but production was cancelled. A single missile and a special upward-looking radar and fire-control system was to be fitted to production aircraft.

MiG-31FE/MF: This designation is applied to the proposed export versions of the MiG-31BM or MiG-31F.

MiG-31LL: One early Foxhound was converted as a dedicated test aircraft (hence the LL, standing for the Russian acronym of 'flying laboratory') for use at the Zhukovsky flight test centre and was used as an ejection seat test-bed. It also reportedly had fairings for cameras on its wingtips.

MiG-31M Foxhound-B: This is the most important and capable Foxhound variant yet produced. Under development since 1984 and first flown on 21 December 1985, it was designed as a radically improved interceptor with upgraded engines, accommodation, avionics, weapons and more fuel. It incorporates new engines with modified nozzles, a one-piece rounded windscreen, small side windows only for the rear cockpit, a wider and deeper dorsal spine containing 300 litres (66 gallons) of additional fuel and a fully retractable refuelling probe mounted on the starboard side of the fuselage. As a result of internal changes, fuel weight is increased to a massive 16 350 kg (36 045 lb). The wings were modified with larger curved root extensions and smaller upper wing fences. The tail was also modified with taller fins featuring more rounded tips with flush dielectric areas at the front and rear. All systems were upgraded, some of the changes consisting of: digital flight controls, multifunction cathode ray tube (CRT) cockpit displays (three are fitted in the rear cockpit), a non-retractable pod with collimated infrared search and track sensor and laser ranger. A new multimode Zaslon-M phased-array radar was introduced, with a larger 1.4 metre (55 in) diameter antenna housed in a 3º downward inclined nose. Detection range has been vastly improved and is extended to 360 km (225 miles).

Weapons fit was changed with the gun being deleted and the number of fuselage weapon stations increased to six by adding two centreline stations for R-37 air-to-air missiles, which can be fired in salvo and then seek out different targets, in addition to the side-mounted R-37s or R-33s. There are also four new underwing pylons were added for R-77 AAMs. An R-37 was first successfully launched from a MiG-31M in October 1993.

The first prototype, produced by the conversion of a MiG-31B, was lost on 9 August 1991 but was followed by five of six more prototypes. At least one had cylindrical wingtip ECM/ECCM (electronic countermeasures/electronic counter-countermeasures) jammer pods with upper and lower fins. Maximum takeoff weight was raised to 52 000 kg (114 640 lb), with increased thrust D-30F6M engines to compensate. Development of the advanced MiG-31M seems to have halted due to funding cuts and has not been ordered into production.

MiG-31S: The designation is applied to a projected commercial variant for the launching of small satellites. It would carry the Fakel OKB Micron missile capable of delivering a 100 kg (220 lb) payload into a 200 km (124 mile) orbit. It could also launch the Aerospace Rally System rocket-powered suborbital glider for astronaut training, atmospheric research or space tourism.


As Russia's most capable air defence interceptor, the MiG-31 remains a powerful threat deterrent for the Russian (and Kazakhstan) Air Force. It has evolved into a highly-developed, advanced aircraft and, as the Russians want to keep their Foxhounds in service until at least 2010, further improved upgrades can be expected in the near future. Whatever the case, these important machines will still be flying for many more years to come.

The MiG-31M

1 The R-77 is designated AA-12 'Adder' by NATO and is an active radar homing or inertially guided AAM with a range of 75 km (47 miles). The Kh-58, designated AS-11 'Kilter' by NATO, is an anti-radiation missile guided inertially or by passive radar homing and has a range of 160 km (100 miles). Kh-31P-1 and Kh-31P-2 missiles, designated AS-17 'Krypton' by NATO, are ARMs guided inertially or by passive radar homing. The Kh-31P-1 has a range of 100 km (62 miles), while the Kh-31P-2 has a range of 200 km (124 miles).

2 The R-37, designated AA-X-13 by NATO, is a long-range inertially or active radar homing guided AAM with a range of 150 km or 93 miles. The R-77M-PD is an improved variant of the 'Adder' AAM with a range of 150 km (93 miles) and is guided inertially or by active radar homing.

3 The Kh-29L (NATO AS-14 'Kedge') is a semi-active laser guided air-to-surface missile with a range of 10 km (6 miles). A number of later variants were produced - the Kh-29T is TV guided with a range of 12 km (7 miles) and the Kh-29TE is also TV guided but with a much longer range of 30 km (19 miles). The Kh-59 (NATO AS-13 'Kingbolt') is a TV guided air-to-surface missile with a range of 160 km (100 miles).

The rear cockpit of the MiG-31 Foxhound

This article was published in the December 2006 edition of Air Forces Monthly Magazine.


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