SVUG-25P / Ye155P / HG-25PD / MiG25PDS / §4

The Ye-155P high-altitude supersonic interceptor project was con­firmed by a decree of the council of ministers in February 1962 But in fact the ОКБ had started the preliminary design two years earlier Con­trary to what was thought, the project was not intended to face the

Canard surfaces could be affixed to the auxiliary structures located near the top of the air intake duct on the Ye-155P prototype of the MiG-25P, The wing pylons held R-40 air-to-air missiles.

threat represented by the American XB-70 Walkyrie Mach 3 bomber. Instead, it was a response to the Lockheed A-l 1.

By listing all of the advancements that the MiG-25 was about to inherit, its technical evolution can be better appreciated:

—a weapon system capable of intercepting any type of flying target, from cruise missiles at low altitudes to supersonic aircraft at veiy high altitudes

—a structure permitting the interceptor to break the heat barrier and fly long supersonic dashes

—high lift-to-drag ratio, good stability, and sharp maneuverability across a wide flight envelope where speed and ceiling were usual­ly favored

—a new (for MiG) aerodynamic scheme with lateral air intakes, twin fins, and two ventral fins

—a structure in welded steel that featured high mass ratio, simple maintenance, good manufacturing regularity due to automation, high output factor for the materials, and lower production costs due to better productivity

One of the seven preproduction MiG-25s fitted with triangular winglets and antiflutter bodies at the wing tips. The wing had no anhedral.

—electronic fuel control (the first in the USSR) and a single refueling point

—a greater number of auto-flight control modes with (for the first time) a range of programming possibilities: for altitude, flights on preset paths, landing approaches, limitations in automatic or semiautomatic flight modes, and overspeed warning —utilization of new materials and semifinished products in high – strength steel, titanium, and heat-resistant duralumin —intensive employment of automatic control systems and flight data recorders

—new technological processes for the heat treatment of materials to alleviate strains and stresses, plus new control and maintenance practices

—a long lifetime and time between overhauls for a combat aircraft of this category

The Ye-155P-l prototype was powered by two Mikulin-Tuman – skiy R-15B-300 turbojets originally rated at 7,350 daN (7,500 kg st) dry and 10,005 daN (10,210 kg st) with afterburner. Its main elements were developed on the R-15-300 that powered the Ye-150 experimen­tal aircraft. Unfortunately, its service life was limited to 150 hours.

The MiG-25PD was equipped with the new RP-25 radar and four pylons under the wing for two R-40 and four R-60 air-to-air missiles.

The internal fuel capacity was considerable: 17,760 1 (4,689 US gal­lons) distributed across built-in tanks in the fuselage and wing. The air inlet control was secured by a small rectangular flap in the lower lip of the air intake and by an internal door (both actuated by elec­tronically controlled cylinders). There was a spill door in the upper panel of the air intake duct, and both turbojets were equipped with adjustable-area nozzles.

If one overlooks the materials and the production processes, the wing had a standard box structure with two main spars attached to fuselage bulkhead nos. 7 and 9, a front spar fixed to the no. 6B frame, and two rear spars fastened to bulkhead nos. 10 and 11. The hinge pin for the flaps was also fixed to bulkhead no. 11. The plain flaps occupied one-third of the trailing edge, as well as the two-section ailerons that measured 2.72 m2 (29.28 square feet). There were two fences on the upper surface of each wing: one as long as the wing chord, roughly along the aileron/flap separation line; the other much smaller, along the aileron sections’ separation line. The wing leading edge had a com­pound sweepback: 42 degrees, 30 minutes at the wing root on half of the LE span, then 41 degrees. On the P-1 prototype the wing had nei­ther dihedral nor anhedral, and the wing tip was fitted with downward – canted winglets. The wing structure was made of welded steel, and its

Hie nose of the MiG-25PDS was lengthened by 250 millimeters (9.84 inches) to house the in-flight refueling probe. The added “slice" can be seen to the right of the “45." skin was made partly of titanium (especially on the leading edge) and partly of D19 duralumin.

The structural backbone of the fuselage consisted of fourteen bulk­heads (the first one level with the cockpit windshield, nos. 13 and 14 supporting the stabilator fulcrum pins on either side of the engine noz­zles) and many frames and stringers. The air intake ducts were not added up but were built-in members. The nose, made of nonconduc – tive material, housed the dish antenna for the Smerch-A ("whirlwind") radar, which could automatically lock on and track aerial targets within 50 km (31 miles). Behind the radar was the electronics compartment and the cockpit, whose canopy was hinged to open starboard. The inner walls of the air intake duct were separated from the fuselage to form a boundary layer bleed.

The airbrakes were located at the rear of the fuselage astride the engine nozzles, one atop the fuselage immediately ahead of the tail chute canister and one underneath it; they fit the curves of the nozzle closely. Both landing lights retracted into the lower wall of the air intake ducts. The tail unit comprised two fins canted outward (11 degrees) and a slab tailplane (sweep of 50 degrees at the leading edge and 9.81 m2 [105.6 square feet] in area). Two large ventral fins—whose size was later reduced—were located under the engine nozzles. On the prototypes a canard surface could be installed on either side of the air intake duct to act as a destabilizing device on some flight regimes This strategy was tested on the Ye-8 The tricycle gear consisted of a twin wheel forward-retracting nose unit and a single wheel with high-pres- sure tires 1 3 m (51 2 inches) in diameter on each forward-retracting mam unit Those wheels were stowed vertically in the side walls of the air intake duct

Though it was designed first, the Ye-155P-l made its premier flight after the Ye-155R-1 reconnaissance variant. Engineers took advantage of the knowledge acquired during the R-l flight tests to make a number of modifications

—the canard surface was discarded as useless

– the area of the fins was increased significantly to 8 m2 (86.1 square feet) apiece

—the chord of the ventral fins was reduced subsequently (they tend­ed to touch at landing)

—the winglets were removed, but the wing tips were fitted with an antiflutter body

—the wing was given a 5-degree anhedral (before that modification seven preproduction machines had triangular end plates at the wing tips)

—after the displacement of its fulcrum pms, the slab tailplane had a taileron capability at high speeds meaning that the two halves could operate in unison (for pitch) or differentially (for roll)

All of these modifications increased the maximum indicated air­speed to 1 300 km/h (702 kt) As was standard practice for new aircraft the ОКБ tried hard to improve its operational availability, service life, and time between overhauls

The Ye-155P-l was first piloted by Ostapyenko on 9 September 1964 (six months after the Ye-155R-1) but was not certified until 1970; it entered service with the WS only in 1973, though mass production had started four years earlier The official decree by the council of min­isters commissioning the aircraft for the Soviet air force was signed on 13 April 1972 Close scrutiny of those dates indicates that the MiG-25 suffered repeatedly from childhood diseases This is not surprising in view of the project’s many innovations There were problems with the stabilator in its taileron mode. There were problems with the ailerons There were problems with the dangerous asymmetry noticed at high speeds whenever a single missile was fired from a wing station Auto­matic trim resolved the taileron shortcomings, and all others were set­tled by V Gordyenko, the LII test pilot There were also concerns about engine TBO that could not be solved—for want of money

The Ye-155P-l prototype was armed with two R-40 air-to-air mis­siles, but the production M1G-25P could carry four of them plus two infrared-guided R-40Ts and two radar-guided R-40Rs. Its primary equip­ment included the Smerch-A radar and the K-10T associated weapon pointing device, the SOD-63 АТС transponder, the SRO-2M/SRZO-2 IFF (transponder/interrogator) whose antennae were flushed in the starboard fin, the Sirena-3 360-degree radar warning receiver whose antennae were set into the center of the antiflutter bodies at the wing tips and at the top of the starboard fin, the RV-UM or RV-4 low-altitude radio-altimeter for 0-600 m (0-1,970 feet), the ARK-10 automatic direc­tion finder, the MRP-56P marker receiver, the SP-50 ILS, the RSBN-6S short-range navigation unit, the R-832M VHF-UHF transceiver, the Prizma HF transceiver, the Lazur command receiver, and the SAU-155 automatic flight control system. The ejection seat was the KM-1 (alti­tude, 0 m; speed, 130 km/h [70 kt]). The МЮ-25Р had two tail chutes with either a circular (60 m2 [646 square feet]) or a cross-shaped canopy (50 m2 [538 square feet]).

Taking into account the experience acquired in the air regiments as well as technological advances, a new version of the aircraft entered production in 1978: the MiG-25PD. It used a new power plant com­posed of two R-15BD-300s—each rated at 8,625 daN (8,800 kg st) dry and 10,975 daN (11,200 kg st) with afterburner—whose service life was extended in stages to 1,000 hours. The Smerch-A radar was replaced by the Sapfir-25 (RP-25), which offered better performance in the automat­ic tracking mode and true look-down/shoot-down capabilities. The MiG-25PD’s armament was supplemented, comprising now two R-40 and four R-60 air-to-air missiles. Infrared sensors were placed under the forward section of the fuselage. The range was increased signifi­cantly by an auxiliary tank attached to the underbelly (developed for the Ye-155R) that could hold 5,300 1 (1,400 US gallons).

As of 1979 all operational MiG-25Ps were upgraded to the MiG – 25PD standard as quickly as they could be sent to overhaul workshops. These modified aircraft received the appellation MiG-25PDS. The MiG – 25PD was mass-produced until 1982. Thanks to the weapon system modifications and improvements to the airframe and engine TBOs, the PVO command announced in 1990 that the MiG-25 would be still oper­ational at the start of the next millennium. The MiG-25 was exported to Algeria, Iraq, Libya, and Syria.

The following details refer to the MiG 25P.

Specifications

Span, 14.015 m (45 ft 11.8 in); length (except probe), 19.75 m (64 ft 9.6 in); wheel track, 3.85 m (12 ft 7.6 in); wheel base, 5.139 m (16 ft 10.3

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МІС-25Р (MiG ОКБ three-view drawing)

in); wing area, 61 4 m2 (660.9 sq ft); takeoff weight with four R-40 mis­siles and 100% internal fuel, 36,720 kg (80,930 lb); takeoff weight in clean configuration with 100% internal fuel, 34,920 kg (76,965 lb); fuel, 14,570 kg (32,110 lb); with 5,300-1 (1,400-US gal) auxiliary tank, 18,940 kg (41,745 lb); wing loading, 598-568.2 kg/m2 (122.6-116.5 lb/sq ft); max operating limit load factor at supersonic speed, 4.5.

Performance

Max speed, 3,000 km/h at 13,000 m (1,620 kt at 42,640 ft); max speed at sea level, 1,200 km/h (648 kt); max Mach number, 2.83; climb to 20,000 m (65,600 ft) in 8.9 min at Mach 2.35; service ceiling, 20,700 m (67,900 ft); landing speed, 290 km/h (157 kt); takeoff speed, 360 km/h (194 kt); range on internal fuel at supersonic speed, 1,250 km (775 mi); at subsonic speed, 1,730 km (1,075 mi); endurance on a coverage mission, 2 h 5 min; takeoff roll, 1,250 m (4,100 ft); landing roll with tail chute, 800 m (2,625 ft).