Mikoyan-Gurevich MiG-25 Foxbat


MiG-25 Foxbat

This was the USSR's answer to the design in the US of fast, high-flying aircraft as the B-70, F-108 and SR-71. The MiG-25 lacked technological refinement, but its performance caused much concern in the west. It was designed to function both as long-range interceptor and reconnaissance aircraft (which in the Middle-East proved invulnerable to the Israeli F-4 Phantom IIs) The center fuselage is a big, welded steel fuel tank, so avionics, radar or cameras are in the nose. Practical speed is limited to Mach 2.83 mainly by controllability problems (available thrust is sufficient to reach Mach 3.2). Main versions are the Mig-25P fighter, the upgraded MiG-25PD fighter, the MiG-25R reconnaissance aircraft, the MiG-25RB 'Foxbat-B' dual-role reconnaissance aircraft and tactical bomber, and the MiG-25BM 'Foxbat-F' defence suppression aircraft. There are two-seat trainer versions of both the fighter and the reconnaissance version. Production of the fighter ended in 1983. The MiG-25 saw combat in several wars in the Middle East. Over 1200 have been built, of which about 75% were interceptors.

Type: MiG-25 Foxbat-E
Country: Soviet Union / Russia
Function: fighter
Year: 1978
Crew: 1
Engines: 2 * 12250kg Tumansky R-31
Wing Span: 13.95 m
Length: 23.82 m
Height: 6.10 m
Wing Area: 56.83m2
Empty Weight: 20000 kg
Max.Weight: 36200 kg
Speed: 3000+ km/h
Ceiling: 24400 m
Range: 1730km

Type: MiG-25PD Foxbat-E
Function: fighter
Year: 1978
Crew: 1
Engines: 2 * 11200kg Tumansky R-15D-300
Wing Span: 14.02 m
Length: 21.67 m
Height: 6.50 m
Max.Weight: 36720kg
Speed: 3000 km/h at 13000m, 1200km/h at S/L
Ceiling: 20700m Range: 1730km
Armament: 4 missiles

Type: MiG-25RB Foxbat-B
Function: reconnaissance / attack
Year: 1970
Crew: 1
Engines: 2 * 10210 kg Tumansky R-15B-300
Wing Span: 13.42 m
Length: 21.55 m
Height: 6.5 m
Empty Weight: 20755
Max.Weight: 41200 kg
Speed: 3000 km/h at 13000 m
Ceiling: 23000 m
Range: 2900 km
Armament: bombs 4000 kg


The MiG-25 Foxbat is a high-performance, high-altitude interceptor. There are several versions of this aircraft: A--basic interceptor; B--reconnaissance; C--two-seat trainer; D--reconnaissance with a modified radar and E. The Foxbat A aircraft, originally designed to counter high-altitude threats, has been converted to Foxbat E, providing a limited low-altitude look-down and shoot-down capabilities somewhat comparable to the MiG-23 Flogger. The wings are high-mounted, swept-back, and tapered with square tips. The aircraft has two turbojet engines and large rectangular air intakes below the canopy and forward of the wing roots. There are dual exhaust. The fuselage is long and slender with solid, pointed nose. The aircraft is box-like from the air intakes to rear section. It has a bubble canopy. On the tail are twin, sweptback, and tapered fins with angular tips. There are flats mid- to low-mounted on fuselage, swept-back, and tapered with angular tips.

Performance

The MiG-25 was capable of exceptional performance, including a maximum speed of Mach 3.0 and a ceiling of 90,000 ft (27,000 m) although a specially modified MIG-25 in 1977 flew to an altitude of 123,524 ft (37,650 m) in 1977. Some believed that the MiG-25 was designed against the SR-71 Blackbird, made to deter, or at least threaten the high altitude, high speed aircraft. However, its maneuverability, range, and close combat potential were extremely limited. Even its tremendous speed was problematic: although the available thrust was sufficient to reach Mach 3.2, a limit of Mach 2.83 had to be imposed to prevent destruction of the engines (at these speeds the engine would start to behave like a ramjet). Even Mach 2.83 was difficult to reach without overspeeding the turbines. The limited maneuverability of the Mig-25 (Maximum acceleration, g-load, rating was just 2.2 g with full fuel tanks, with an absolute limit of 4.5 g) has often been overstated by Western observers, as under the same high performance parameters, the SR-71 has even more restrictive stress limitations.

The maximum speed ever observed for a MiG-25 was Mach 3.2 as recorded by an American radar during a flight over Israel in 1973. The Soviet pilot was conducting a reconnaissance mission over the nation when he was threatened by Israeli surface-to-air missiles. The pilot went to full afterburner and pushed the MiG-25 as fast as it would go to return to the safety of an Egyptian airfield. Though the MiG-25 survived the flight, its engines were completely destroyed and had to be replaced.

Development

The development of the MiG-25 began in the 1950s, paralleling American efforts to develop a Mach 3 bomber and interceptor aircraft, including the (ultimately abortive) XB-70 Valkyrie, the XF-103 Thunderwarrior, the Lockheed YF-12, and the XF-108 Rapier. With the first Mach 2 aircraft beginning to enter service, Mach 3 seemed like the next logical step. A variety of roles were considered, including cruise missile carriers, and even a small five- to seven-passenger supersonic transport, but the main impetus was a new high-altitude reconnaissance aircraft and heavy interceptor. If a Mach 3 bomber were to enter American service, it would be nearly invulnerable to Soviet air defense.

The Mikoyan-Gurevich OKB accepted the assignment effective 10 March 1961. Although the XB-70 Valkyrie was cancelled before the new aircraft, which carried the bureau designation Ye-155, reached the prototype stage, it seemed that the Ye-155 would still be a useful addition to the PVO interceptor force against reconnaissance targets like the SR-71 Blackbird. It was widely believed that the MiG-25 was developed in response to the XB-70. However, A. Belyankov, head of the MiG design bureau confirmed that this was not in fact the case.

The first prototype, which was actually the reconnaissance variant designated Ye-155-R1 by the bureau, made its first flight on 6 March 1964. The prototype interceptor, Ye-155-P1, took to the air on 9 September 1964. Development, which represented a major step forward in Soviet aerodynamics engineering and metallurgy, took several more years to complete. In the meantime, several prototypes, under the cover designation Ye-266, made a series of record-setting flights in 1965, 1966, and 1967.

Series production of the two initial variants, designated MiG-25P ('Foxbat-A') (interceptor) and MiG-25R ('Foxbat-B') (reconnaissance), began in 1969. The MiG-25R entered VVS service almost immediately, but the service entry of the MiG-25P with the PVO was delayed until 1972. A non-combat trainer was also developed for each version, the MiG-25PU ('Foxbat-C') and MiG-25RU, respectively. The MiG-25R evolved several subsequent derivatives, including the MiG-25RB reconnaissance-bomber, the MiG-25RBS and MiG-25RBSh with side-looking airborne radar (SLAR), the MiG-25RBK and MiG-25RBF ELINT aircraft ('Foxbat-D'), and the MiG-25BM ('Foxbat-F') SEAD variant, carrying four Kh-58 (AS-11 'Kilter') anti-radiation missiles.

The MiG-25 was capable of exceptional performance, including a maximum speed of Mach 3.0 and a ceiling of 90,000 ft (27,000 m) although a specially modified MIG-25 in 1977 flew to an altitude of 123,524 ft (37,650 m) in 1977. Some believed that the MiG-25 was designed against the SR-71 Blackbird, made to deter, or at least threaten the high altitude, high speed aircraft. However, its maneuverability, range, and close combat potential were extremely limited. Even its tremendous speed was problematic: although the available thrust was sufficient to reach Mach 3.2, a limit of Mach 2.8 had to be imposed to prevent total destruction of the engines. Even Mach 2.8 was difficult to reach without overspeeding the turbines. The limited maneuverability of the Mig-25 has often been overstated by Western observers, as under the same high performance parameters, the SR-71 has even more restrictive stress limitations.

Despite these limitations, inaccurate intelligence analysis and several false assumptions caused a panic in the West, where it was initially believed that the MiG-25 was actually an agile air-combat fighter rather than a stand-off interceptor. In response, the United States launched an ambitious new program, which resulted in the McDonnell-Douglas F-15 Eagle.

Design

The ambitious project was one of the greatest challenges ever faced by the Soviet aerospace industry and required considerable research to address heating issues at such high speeds. One of the most significant hurdles overcome by the designers was the selection of structural materials capable of surviving the high temperatures near Mach 3. It was estimated that the earlier MiG-21 flying at Mach 2 would experience a peak temperature at its nose of about 225F (107C). The increase in air friction when flying an aircraft at Mach 3 generated a nose temperature nearly three times higher at 572F (300C). Aluminum, the conventional material most planes are made of, begins to fail and deform at a temperature of only 266F (130C) and would clearly not be suitable for the MiG-25.

Designers instead chose welded steel for most of the primary structure with special alloys of steel and titanium for the hottest areas like the nose and wing leading edges. All told, about 80% of the plane's structure was composed of tempered steel, 11% of aluminum, and 8% of titanium. The MiG-25 also required the development of advanced welding techniques to avoid cracking in the heat-resistant alloys. Over 75% of the airframe assembly required some form of welding while conventional riveting accounted for less than a quarter.

The MiG-25 designers also faced considerable aerodynamic challenges in designing the external configuration of the aircraft. The most significant problem was selecting a configuration that provided adequate maneuverability and stability while maintaining high speed and high altitude performance. The best trade-off between these conflicting requirements was found by adopting large but very thin wings mounted high on the fuselage and passing over two large ducts containing the powerful jet engines.

The large wing appears relatively simple at first glance but its shape contains subtle variations in leading edge sweep, dihedral, and airfoil thickness to improve performance. Several options for the wingtip were also explored including a triangular-shaped winglet and an external fuel tank with a large under slung fin. The design ultimately selected featured a large wingtip tubular mass to prevent wing flutter during flight. Much of the wing's interior is dedicated to carrying fuel, and about 70% of the volume of the MiG-25 is taken up by fuel tanks to maximize range and endurance.

Further sophisticated aerodynamic concepts were required for the air inlets. The MiG-25 makes use of variable geometry intakes with adjustable positions to improve engine performance at both low and high speeds. The inlets were placed sufficiently far apart to provide room for the narrow forward fuselage containing the cockpit and large search radar. Heating issues once again proved a dominant factor in designing the fuselage since complex cooling and insulation techniques were required for the avionics, engines, and cockpit. The canopy glass is said to be so hot at maximum speed that the pilot cannot touch it with his bare hand, yet the internal cooling systems maintain a comfortable temperature inside the cockpit.


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