 limit of Mach 2.83 had to be imposed as the turbines tended to overspeed and overheat at higher speeds, possibly damaging them beyond repair.1920
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 was built until production ended in 1982. The improved PD variant that replaced it was built from 1978 till 1984 with 104 aircraft completed.6 But from then on the Gorkii factory switched over production to the new MiG-31.
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.21 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 in Japan.22 The pilot overshot the runway on landing and damaged the front landing gear. Despite Soviet protests, the Japanese invited U.S. Air Force personnel to investigate the aircraft.22 On 25 September, it was moved by a C-5A transport to a base in central Japan, where it was carefully dismantled and analyzed.22 After 67 days, the aircraft was returned by ship to the Soviets, in pieces.22
The analysis, based on technical manuals and ground tests of engines and avionics, revealed unusual technical information:
- Belenko's particular aircraft was brand new, representing the latest Soviet technology.
- The aircraft was assembled quickly, and was essentially built around its massive Tumansky R-15(B) turbojets.
- Welding was done by hand. Rivets with non-flush heads were used in areas that would not cause adverse aerodynamic drag.23
- The aircraft was built of a nickel alloy and not titanium as was assumed (though some titanium was used in heat-critical areas). The steel construction contributed to the craft's 29,000 kg (64,000 lb) unarmed weight.
- Maximum acceleration (g-load) rating was just 2.2 g (21.6 m/s²) with full fuel tanks, with an absolute limit of 4.5 g (44.1 m/s²). One MiG-25 withstood an inadvertent 11.5 g (112.8 m/s²) pull during low-altitude dogfight training, but the resulting deformation damaged the airframe beyond repair.24
- Combat radius was 299 kilometres (186 mi), and maximum range on internal fuel (at subsonic speeds) was only 1,197 kilometres (744 mi) at low altitude (< 1000 meter).6
- The airspeed indicator was redlined at Mach 2.8, with typical intercept speeds near Mach 2.5 in order to extend the service life of the engines.22 A MiG-25 was tracked flying over Sinai at Mach 3.2 in the early 1970s, but the flight led to the destruction of its engines.23
- The majority of the on-board avionics were based on vacuum-tube technology, not solid-state electronics. Although they represented aging technology, vacuum tubes were more tolerant of temperature extremes, thereby removing the need for environmental controls in the avionics bays. The vacuum tubes were also easy to replace in remote northern airfields where sophisticated transistor parts might not have been readily available. With the use of vacuum tubes, the MiG-25P's original Smerch-A (Tornado, NATO reporting name "Foxfire") radar had enormous power – about 600 kilowatts. As with most Soviet aircraft, the MiG-25 was designed to be as rugged as possible. The use of vacuum tubes also makes the aircraft's systems resistant to an electromagnetic pulse, for example after a nuclear blast.25
As the result of Belenko's defection and the compromise of the MiG-25P's radar and missile systems, beginning in 1976, the Soviets started to develop an advanced version, the MiG-25PD ("Foxbat-E").6
Plans for a new aircraft to develop the Foxbat's potential to go faster than the in-service limit of Mach 2.8 were designed as a flying prototype. Unofficially designated MiG-25M, it had new powerful engines R15BF2-300, improved radar, and missiles. This work never resulted in a machine for seri