The Mikoyan MiG-31 (Russian: МиГ-31) (NATO reporting name "Foxhound") is a supersonic interceptor aircraft developed to replace the MiG-25 'Foxbat'. The MiG-31 was designed by the Mikoyan design bureau based on the MiG-25. The MiG-31 was the most recent interceptor fielded by the Soviet Union before its dissolution.
The MiG-25 'Foxbat', despite Western panic about its tremendous performance, made substantial design sacrifices in capability for the sake of achieving high speed, altitude, and rate of climb. It lacked manoeuverability at interception speeds, was difficult to fly at low altitudes, and its inefficient turbojet engines resulted in a very short combat range at supersonic speeds. The MiG-25's speed gauge was redlined at Mach 2.8, and pilots were instructed not to top Mach 2.5 in order to preserve the engines. Achieving the MiG-25's maximum potential speed of Mach 3.2 would result in the destruction of the engines.
Development of the MiG-25's replacement began with the Ye-155MP (Russian: Е-155МП
prototype which first flew on 16 September 1975. Although it bore a superficial resemblance to a stretched MiG-25 (with a longer fuselage for the radar operator cockpit), it was in many respects a totally new design. Soviet manufacturing limitations forced the MiG-25 to use nickel steel for 80% of its structure. The Ye-155MP doubled the use of titanium to 16% and tripled the aluminum content to 33% to reduce structural mass. More importantly, supersonic speed was now possible at low-level altitudes. Fuel capacity was also increased, and new, more efficient low-bypass-ratio turbofan engines were fitted.
The most important development was the introduction of an advanced radar capable of both look-up and look-down engagement (locating targets above and below the aircraft), as well as multiple target tracking. This finally gave the Soviets an interceptor capable of engaging the most likely Western intruders at long range. It also reflected a policy shift from reliance on ground-controlled interception (GCI) to greater autonomy for flight crews.
Like its MiG-25 predecessor, the MiG-31 was surrounded by early speculation and misinformation concerning its design and capabilities. The West learned of the new interceptor from Lieutenant Viktor Belenko, a pilot who defected to Japan in 1976 with his MiG-25P. Belenko described an upcoming "Super Foxbat" with two seats and a capability to intercept cruise missiles. According to his testimony, the new interceptor was to have air intakes similar to the MiG-23 'Flogger', which the MiG-31 in reality does not have, at least not in production variants. While undergoing testing, a MiG-31 was spotted by a reconnaissance satellite at the Zhukovsky flight test center near the town of Ramenskoye. The images were interpreted as a fixed-wing interceptor version of a swing-wing fighter codenamed the "Ram-K". The latter was eventually revealed to be the Sukhoi Su-27 'Flanker', a wholly unrelated design.
Series production of the MiG-31 began in 1979, with operational models entering Soviet Anti-Air Defense (PVO) service in 1982. It was first photographed by a Norwegian pilot over the Barents Sea in 1985.
The MiG-31 was sought after for a variety of long-range missions. Following the collapse of the USSR, however, the budget for spares (MIG31 AOG desk was created to solve this problem) and maintenance collapsed, leaving many squadrons unable to maintain their complex aircraft. By 1996, only 20% of remaining aircraft were reportedly serviceable at any time; however, by early 2006, a stronger Russian economy permitted the return to service of around 75% of the Russian Air Force's (VVS'
About 500 MiG-31s were produced, approximately 370 of which remain in Russian service, with another 30 or so in Kazakhstan. Some upgrade programs have found their way in the MiG-31 fleet, like the MiG-31BM multirole version with upgraded avionics, new multimode radar, hands-on-throttle-and-stick (HOTAS) controls, liquid-crystal (LCD) color multi-function displays (MFDs), ability to carry the AA-12 'Adder' missile and various Russian air-to-ground missiles (AGMs) such as the AS-17 'Krypton' anti-radiation missile (ARM), a new and more powerful computer, and digital datalinks. However, only very small number of Russian aircraft have been upgraded to the MiG-31BM standard, although others have been equipped with the new computer and the ability to carry the R-77 long-range missile as well.
The MiG-31 is likely that it will continue serving for years to come, depending on its upgrades and the growth of the Russian economy which has upgraded the plane recently.
Like the MiG-25, the Foxhound is a large twin-engine aircraft with side-mounted air intakes, a shoulder-mounted wing with an aspect ratio of 2.94, and twin vertical tailfins. Unlike the Foxbat, it has two seats, with the rear occupied by a dedicated weapon systems officer.
 Airframe and engines
MiG-31 'Foxhound' in flight
The wings and airframe of the MiG-31 are stronger than those of the MiG-25, permitting supersonic flight at low altitudes. Its Aviadvigatel D30-F6 turbofans, rated at 34,000 lbf thrust, (also described as "bypass turbojets" due to the low bypass ratio) allow a maximum speed of Mach 1.23 at low altitude. High-altitude speed is temperature-redlined to Mach 2.83 the thrust-to-drag ratio is sufficient for speeds in excess of Mach 3, but such speeds pose unacceptable hazards to engine and airframe life in routine use.
Given the MiG-31's role as Mach 2.8+ interceptor and the sustained afterburning this requires, its fuel consumption is higher when compared to other aircraft serving in different roles, such as the Su-27. As a result, the aircraft's fuel fraction has been increased to more than 0.40 16,350 kg (36,050 lb) of high-density T-6 jet fuel. The outer wing pylons are also plumbed for drop tanks, allowing an extra 5,000 l (1,320 US gal) of external fuel. Late-production aircraft have aerial refueling probes.
Despite the stronger airframe, the Foxhound is limited to a maximum of 5 g at supersonic speeds. At combat weight, its wing loading is marginal and its thrust to weight ratio is favorable. However, it is not designed for close combat or rapid turning.
 Electronics suite
MiG-31 'Foxhound' showing its Zaslon phased-array radar
The MiG-31 was the world's first operational fighter with a passive electronically scanned array radar, the Zaslon S-800. Its maximum range against fighter-sized targets is approximately 200 km (125 mi), and it can track up to 10 targets and simultaneously attack four of them with its AA-9 'Amos' missiles. It is claimed to have limited astern coverage (perhaps the reason for the radome-like protuberance above and between the engines). The radar is matched with an infrared search and tracking (IRST) system in a retractable undernose fairing. Up to four MiG-31s, spaced up to 200 km (125 mi) apart to cover a wide swath of territory, can coordinate via datalink.
The MiG-31M-, MiG-31D-, and MiG-31BS-standard aircraft have an upgraded Zaslon-M passive electronically scanned phased array radar (PESA) with larger antenna and greater detection range (said to be 400 km (250 mi) against AWACS-size targets) and the ability to attack multiple targets -air and ground- simultaneously. The back-seater's controls are replaced with modern MFDs. Its electronic countermeasures capabilities have also been upgraded, with new ECM pods on the wingtips.
The aircraft is a two-seater with the rear seat occupant controlling the radar. Although cockpit controls are duplicated across cockpits, it is normal for the aircraft to be flown only from the front seat. The pilot flies the aircraft by means of a centre stick and left hand throttles. The rear cockpit has only two small vision ports on the sides of the canopy. It is argued that the presence of the WSO (Weapon Systems Operator) in the rear cockpit improves aircraft effectiveness since he is entirely dedicated to radar operations and weapons deployment. This decreases the workload of the pilot and increases efficiency.
Both cockpits are fitted with zero/zero ejection seats which allow the crew to eject at any altitude and airspeed.
Some upgrade programmes have found their way to the MiG-31 fleet, for example the MiG-31BM multi-role version which includes upgraded avionics. In the cockpit this upgrade provides for the use of new weapons, a new multimode radar, HOTAS controls and liquid-crystal (LCD) colour multi-function displays (MFDs). Only a small part of the fleet, however, has been upgraded to this standard .
It has been claimed by Russian Federation Defence Ministry chief Colonel Yuri Balyko, that the upgrade will increase the combat effectiveness of the aircraft several times over. 
MiG-31 'Foxhound' armed with R-33 (AA-9 'Amos'
The MiG-31's main armament is four R-33 air-to-air missiles (NATO codename AA-9 'Amos'
carried under the belly. The R-33 is the Russian equivalent of the U.S. Navy's AIM-54 Phoenix. It can be guided in semi-active radar homing (SARH) mode, or launched in inertial guidance mode with the option of mid-course updates from the launch aircraft and switching to SARH for terminal guidance. A more advanced version of the weapon, the AA-X-13 'Arrow', which is the replacement for the older R-33, features folding stabilizers to reduce its stored size.
Other weapons include the old AA-6 'Acrid', originally deployed on the MiG-25, and the AA-8 'Aphid' or AA-11 'Archer' short-range IR missiles, carried on wing pylons. Currently the entire MiG-31 fleet is being refitted to carry the newer AA-12 'Adder' on the wing pylons.
Unlike the MiG-25, the MiG-31 has an internal cannon, a six-barrel, 23 mm GSh-6-23 with 800 rounds of ammunition, mounted above the starboard main landing gear bay. The GSh-6-23 has a claimed rate of fire of over 10,000 rounds per minute.
Russian Air Force MiG-31BM on display
A new version of the 'Foxhound' with upgraded avionics, the MiG-31B, was introduced in 1990. Its development was the result of the Soviet discovery that Phazotron radar division engineer Adolf Tolkachev had sold information on advanced radars to the West. Tolkachev was executed, and a new version of the compromised radar was hastily developed. Many earlier MiG-31s were upgraded to the new standard, designated MiG-31BS.
Development of a more comprehensive advanced version, the MiG-31M, began in 1983 and first flew in 1986, but the collapse of the Soviet Union prevented it from entering full production. Since 1991 and especially since 2000, most of the existing aircraft have been upgraded to the MiG-31M standard, also adding some additional features like Global Positioning System (GPS) and GLONASS receivers, and three colour CRT MFDs in the rear cockpit. (In the VVS, aircraft designations are often repeated through the years; for example, the Su-35 'Flanker-E' and Su-37 'Flanker-F' are both designated "Su-27M".)
It was the heaviest interceptor in the world, with a maximum takeoff weight on 56 tonnes. It was even heavier than a commercial Tu-134 which has a maximum takeoff weight of 49 tonnes.
Several other variants have been developed, including a dedicated anti-satellite missile carrier, the MiG-31D; a similar satellite-launching aircraft, MiG-31A; a proposed multi-role version, MiG-31F; and a downgraded export version, MiG-31E; but most have not been built in any quantity, if at all.
* Kazakhstan Air Force has 33 in service, 10 to be refurbished.
* Russian Air Force 286 in service, 100 in reserve.
* Russian Naval Aviation
* Syrian Air Force ordered 8 MiG-31E aircraft in 2007. However, the order has been suspended in May 2009 reportedly either due to Israeli pressure or lack of Syrian funds.
 Former operators
* Soviet Anti-Air Defence
* Soviet Air Force aircraft passed on to Russia and Kazakhstan in 1991.
 Specifications (MiG-31)
Data from Great Book of Modern Warplanes, MiG-31E data
* Crew: Two (pilot and weapons system officer)
* Length: 22.69 m (74 ft 5 in)
* Wingspan: 13.46 m (44 ft 2 in)
* Height: 6.15 m (20 ft 2 in)
* Wing area: 61.6 m² (663 ft²
* Empty weight: 21,820 kg (48,100 lb)
* Loaded weight: 41,000 kg (90,400 lb)
* Max takeoff weight: 46,200 kg (101,900 lb)
* Powerplant: 2× Soloviev D-30F6 afterburning turbofans
o Dry thrust: 93 kN (20,900 lbf) each
o Thrust with afterburner: 152 kN (34,172 lbf) each
* Maximum speed:
o High altitude: Mach 2.83 (3,000 km/h, 1,860 mph)
o Low altitude: Mach 1.2 (1,500 km/h, 930 mph)
* Combat radius: 720 km (450 mi) at Mach 2.35
* Ferry range: 3,300 km (2,050 mi)
* Service ceiling: 20,600 m (67,600 ft)
* Rate of climb: 208 m/s (41,000 ft/min)
* Wing loading: 665 kg/m² (136 lb/ft²
* Thrust/weight: 0.85
* Maximum g-load: 5 g
* 1× GSh-6-23 23 mm cannon with 260 rounds.
* Fuselage recesses for 4× R-33 (AA-9 'Amos'
or (for MiG-31M/BM only) ×6 R-37 (AA-X-13 'Arrow'
long-range air-to-air missiles.
* Four underwing pylons for a combination of:
* two R-40TD1 (AA-6 'Acrid'
medium-range missiles, and
* 4× R-60 (AA-8 'Aphid'
or R-73 (AA-11 'Archer'
short-range IR missiles, or
* 4× R-77 (AA-12 'Adder'
* Some aircraft are equipped to launch the Kh-31P (AS-17 'Krypton'
and Kh-58 (AS-11 'Kilter'
anti-radiation missiles in the suppression of enemy air defenses (SEAD) role