The MiG-31 ‘Foxhound’ was developed to counter the threat posed by new low-level strike aircraft and cruise missiles, complementing the Su-27 in service, and using its ultra-long-range capability to fill gaps in Russia’s ground-based radar chain. A two-seat derivative of the MiG-25 ‘Foxbat’ airframe, the ‘Foxhound’ introduced an all-new structure, a new wing planform with small LERXes, Soloviev D-30F-6 turbofans and a new undercarriage. The Ye-155MP prototype flew on 16 September 1975 and series production of 280 MiG-31 s began in 1979.
The MiG-31 featured a flat belly with four missile recesses for its primary armament, which consisted of R-33 (AA-9 ‘Amos’) AAMs. The ‘Foxhound’ also carries a scabbed-on GSh-6-23 six-barrelled 23-mm cannon pod and has underwing pylons for two AA-6 ‘Acrid’ or four AA-8 ‘Aphid’ missiles. The new ‘Zaslon’ radar had a phased-array antenna, increasing range and allowing faster, more accurate beam pointing. Ten targets can be tracked simultaneously, and four engaged. Groups of four MiG-31s can operate independently of ground control, covering a 900-km (560-mile) swathe of territory, with the leader automatically controlling his wingmen.
The MiG-31 01-DZ introduced a retractable inflight refuelling probe, while the MiG-31B also had an improved radar with better ECCM, and a new digital processor. Existing aircraft brought up to the same standard were designated MiG-31 BS.
Two MiG-31 D prototypes were produced as test-beds for a new anti-satellite missile. The MiG-31E, MiG-31F and MiG-31FE designations were applied to unbuilt export and upgrade configurations, while the MiG-31BM is a proposed defence suppression variant.
The improved MiG-31M interceptor variant was built in prototype form only. The MiG-31 M carried six R-37 long-range AAMs in three side-by-side recesses under the belly, each accommodating tandem pairs of missiles. Its new radar had a 1,4-m diameter antenna and could simultaneously engage six targets. A fully-retractable IRST was fitted, and MiG-31 Ms also have a redesigned rear cockpit, with three CRT MFDs. Other changes include a one-piece canopy and windscreen, a retractable IFR probe, large wingtip ESM pods, and aerodynamic refinements. Redesigned LERXes improved high AoA handling, and a bulged spine gave increased fuel capacity, but development was abandoned due to lack of funding. The first of six prototypes made its maiden flight on 21 December 1985.