Sukhoi Su-24

The Sukhoi Su-24 (NATO reporting name: Fencer) is a supersonic, all-weather tactical bomber developed in the Soviet Union. The aircraft has a variable-sweep wing, twin engines and a side-by-side seating arrangement for its crew of two. It was the first of the USSR's aircraft to carry an integrated digital navigation/attack system.

The Su-24 started development in the early 1960s and first flew in 1967. It entered service in 1974 and production ceased in 1993. It remains in service with the Russian Aerospace Forces, Iranian Air Force, Ukrainian Air Force, Algerian Air Force and various other air forces to which it was exported.

Development

Background

One of the conditions for accepting the Sukhoi Su-7B into service in 1961 was the requirement for Sukhoi to develop an all-weather variant capable of precision air strikes. Preliminary investigations with S-28 and S-32 aircraft revealed that the basic Su-7 design was too small to contain all the avionics required for the mission. OKB-794 (later known as Leninets) was tasked with developing an advanced nav/attack system, codenamed Puma, which would be at the core of the new aircraft. That same year, the United States proposal for their new all-weather strike fighter would be the TFX. The resulting F-111 would introduce a variable-geometry wing for greatly increased payload, range, and low-level penetration capabilities.

In 1962–1963, Sukhoi initially set out to build an aircraft without the complexity of moving wings like the F-111. It designed and built a mockup of S-6, a delta wing aircraft powered by two Tumansky R-21 turbojet engines and with a crew of two in a tandem arrangement. The mockup was inspected but no further work was ordered due to lack of progress on the Puma hardware.

In 1964, Sukhoi started work on S-58M. The aircraft was supposed to represent a modification of the Sukhoi Su-15 interceptor (factory designation S-58). In the meantime, revised Soviet Air Force requirements called for a low-altitude strike aircraft with STOL capability. A key feature was the ability to cruise at supersonic speeds at low altitude for extended periods of time in order to traverse enemy air defenses. To achieve this, the design included two Tumansky R-27 afterburning turbojets for cruise and four Rybinsk RD-36-35 turbojets for STOL performance. Side-by-side seating for the crew was implemented since the large Orion radar antennas required a large frontal cross-section. To test the six-engine scheme, the first Su-15 prototype was converted into S-58VD flying laboratory which operated in 1966–1969.

Design phase

The aircraft was officially sanctioned on 24 August 1965 under the internal codename T-6. The first prototype, T-6-1, was completed in May 1967 and flew on 2 July with Vladimir Ilyushin at the controls. The initial flights were performed without the four lift jets, which were installed in October 1967. At the same time, R-27s were replaced with Lyulka AL-21Fs. STOL tests confirmed the data from S-58VD that short-field performance was achieved at the cost of significant loss of flight distance as the lift engines occupied space normally reserved for fuel, loss of under-fuselage hardpoints, and instability during transition from STOL to conventional flight. So the six-engine approach was abandoned.

By 1967, the F-111 had entered service and demonstrated the practical advantages and solutions to the technical problems of a swing-wing design. On 7 August 1968, the OKB was officially tasked with investigating a variable geometry wing for the T-6. The resulting T-6-2I first flew on 17 January 1970 with Ilyushin at the controls. The subsequent government trials lasted until 1974, dictated by the complexity of the onboard systems. The day or night and all-weather capability was achieved – for the first time in Soviet tactical attack aircraft – thanks to the Puma nav/attack system consisting of two Orion-A superimposed radar scanners for nav/attack, a dedicated Relyef terrain clearance radar to provide automatic control of flights at low and extremely low altitudes, and an Orbita-10-58 onboard computer. The crew was equipped with Zvezda K-36D ejection seats, allowing them to bail out at any altitude and flight speed, including during takeoff and landing. The resulting design with a range of 3,000 kilometers (1,900 mi) and payload of 8,000 kilograms (18,000 lb) was slightly smaller and shorter ranged than the F-111.

Ten fatal accidents occurred during Su-24 development, killing thirteen Sukhoi and Soviet Air Force test pilots, and more than 5 crashes per year were occurring at average after that

The first production aircraft flew on 31 December 1971 with V.T. Vylomov at the controls, and on 4 February 1975, T-6 was formally accepted into service as the Su-24. About 1,400 Su-24s were produced.

Upgrades

Surviving Su-24M models have gone through a life-extension and updating program, with GLONASS, upgraded cockpit with multi-function displays (MFDs), HUD, digital moving-map generator, Shchel helmet-mounted sights, and provision for the latest guided weapons, including R-73 (AA-11 'Archer') air-to-air missiles. The upgraded aircraft are designated Su-24M2.

Design

The Su-24 has a shoulder-mounted variable geometry wing outboard of a relatively small fixed wing glove, swept at 69°. The wing has four sweep settings: 16° for takeoff and landing, 35° and 45° for cruise at different altitudes, and 69° for minimum aspect ratio and wing area in low-level dashes. The variable geometry wing provides excellent STOL performance, allowing a landing speed of 230 kilometers per hour (140 mph), even lower than the Sukhoi Su-17 despite substantially greater takeoff weight. Its high wing loading provides a stable low-level ride and minimal gust response.

The Su-24 has two Saturn/Lyulka AL-21F-3A afterburning turbojet engines with 109.8 kN (24,700 lbf) thrust each, fed with air from two rectangular side-mounted intakes with splitter plates/boundary-layer diverters.

In early Su-24 ("Fencer A" according to NATO) aircraft these intakes had variable ramps, allowing a maximum speed of 2,320 kilometers per hour (1,440 mph), Mach 2.18, at altitude and a ceiling of 17,500 meters (57,400 ft). Because the Su-24 is used almost exclusively for low-level missions, the actuators for the variable intakes were removed to reduce weight and maintenance. This has no effect on low-level performance, but absolute maximum speed and altitude are cut to Mach 1.35 and 11,000 meters (36,000 ft). The earliest Su-24 had a box-like rear fuselage, which was soon changed in production to a rear exhaust shroud more closely shaped around the engines to reduce drag. The revised aircraft also gained three side-by-side antenna fairings in the nose, a repositioned braking chute, and a new ram-air inlet at the base of the tail fin. The revised aircraft were dubbed "Fencer-B" by NATO, but did not merit a new Soviet designation.

Armament

The Su-24's fixed armament is a single fast-firing GSh-6-23 cannon with 500 rounds of ammunition, mounted in the fuselage underside. The gun is covered with an eyelid shutter when not in use. Two or four R-60 (NATO AA-8 'Aphid') infrared missiles are usually carried for self-defence by the Su-24M/24MK.

Initial Su-24s had basic electronic countermeasures (ECM) equipment, with many Su-24s limited to the old Sirena radar-warning receiver with no integral jamming system. Later-production Su-24s had more comprehensive radar warning, missile-launch warning, and active ECM equipment, with triangular antennas on the sides of the intakes and the tip of the vertical fin. This earned the NATO designation "Fencer-C", although again it did not have a separate Soviet designation. Some "Fencer-C" and later Su-24M (NATO "Fencer-D") have large wing fence/pylons on the wing glove portion with integral chaff/flare dispensers; others have such launchers scabbed onto either side of the tail fin.

Operational history

Substantial numbers of ex-Soviet Su-24s remain in service with Kazakhstan, Russia, and Ukraine. In 2008, roughly 415 were in service with Russian forces, with 321 in the Russian Air Force and 94 in the Russian Navy. The Russian Aerospace Forces will eventually replace the Su-24 with the Sukhoi Su-34.

Soviet–Afghan War

The Soviet Union used some Su-24s in the Soviet–Afghan War, with an initial round of strikes in 1984 and a second intervention at the end of the war in 1988. No Su-24 was lost.

Lebanese Civil War

On October 13, 1990, Syrian Air Force jets entered Lebanese airspace in order to strike General Michel Aoun's military forces. Seven Su-24s were used in this operation.

Operation Desert Storm

During Operation Desert Storm, the Iraqi Air Force evacuated 24 of its 30 Su-24MKs to Iran. Another five were destroyed on the ground, while the sole survivor remained in service after the war.