Su-27SK/UBK Flanker Air Superiority Fighter Aircraft

Su-27SK/UBK Air Superiority Fighter Aircraft

The Sukhoi Su-27 (NATO codename: Flanker) is the twin-engine front-line fighter aircraft designed by the Russian Sukhoi Design Bureau in the late 1970s as a counter to the U.S. third-generation air-superiority fighters such as F-14 and F-15. The PLA Air Force (PLAAF) has acquired three batches totalling 76 Su-27 fighters from Russia since 1992. Two variant are currently serving with the PLAAF: the single-seat Su-27SK fighter manufactured by KnAAPO at Komsomolsk-na-Amur and the two-seat Su-27UBK fighter-trainer manufactured by IAPO at Irkusk. The Su-27SK is also built under license at Shenyang Aircraft Industry Co. (SAC) as the Jian-11.

High-level negotiations between Beijing and Moscow over a possible fighter deal began in 1990. Soviet pilots demonstrated the Mikoyan-Gurevich MiG-29 Fulcrum and Sukhoi Su-27 Flanker fighters in Beijing in March 1991. After careful evaluations, the PRC signed the contract of 26 Su-27 fighters, including 20 single-seat Su-27SK (Flanker-B) and 6 two-seater Su-27UBK (Flanker-C). The delivery of these aircraft was completed by 1992, making the PRC the first non-CIS country to operate the Su-27. These aircraft were initially operated by the PLAAF 3rd Aviation Division / 7th Fighter Regiment based at Wuhu AFB, Anhui Province, and later transferred to 19th Air Division / 55th Fighter Regiment based at Jining, Henan Province.

One of the first batch Su-27SK delivered to the PLAAF in 1992 (Chinese Internet)

After showing interest in 1993 in acquiring a second batch of the Su-27, the PRC ordered 22 of the fighters (16 Su-27SKs and 6 Su-27UBKs) in 1995 in a deal worth about US$710 million. In reporting to the United Nations, both the PRC and Russia confirmed that the transfer of 22 aircraft took place in 1996. A Russian source noted that China requested special modifications for its aircraft, which included strengthened landing gear to enable the aircraft to carry its designed fuel load and enable its intended 1,400km combat radius. These aircraft are operated by an aviation regiment organic to the PLAAF 2nd Aviation Division based on Suixi AFB, Guangdong Province.

In 1995, the PRC expressed interest in a licensed co-production of the Su-27SK single-seat fighter. In 1996, Sukhoi Company (JSC) and Shenyang Aircraft Corporation (SAC) entered into a contract worth US$2.5 billion for the co-production of 200 Su-27SK fighters as the J-11. Under the terms of the agreement, Sukhoi/KnAAPO would supply the aircraft in kit form to be assembled in SAC. Russia was also responsible for supplying the PRC with the avionics suite and AL-31F turbofan engines for the J-11 production.

The shortage of comparable training aircraft in the PLAAF for the new Su-27 pilots started to emerge in the late 1990s. This has resulted in the purchase of the third batch of 28 Su-27s, all in the two-seat UBK fighter-trainer variant, in 1999. These aircraft were delivered to the PLAAF in 2002 and are deployed by an aviation regiment organic to the PLAAF 33rd Aviation Division based at Baishiduo AFB, Chongqing.

The Su-27 is the first PLAAF fighter aircraft capable of competing with modern Western fighters. The aircraft was demonstrated to the public for the first time during the 1996 PLA exercise to intimidate Taiwan, when China Central Television broadcasted images of PLAAF Su-27s flying in four-plane formation and attacking ground targets with unguided bombs and rockets. Later in the summer of 1999, Suixi-based Su-27s also flew round-trip missions over the Taiwan Strait during the PLA joint exercises. At least five Su-27s were reportedly destroyed during a typhoon in 1998, with several more lost during flight training over the years.

The limitations of the Su-27, however, soon became apparent to the PLAAF. As a single mission air superiority fighter, it could only perform secondary attack missions, and only with “dumb” munitions that include a range of free-fall bombs and unguided rockets. Using such munitions in combat unnecessarily exposes the expensive fighter to enemy air defence systems. This later led to the decision to purchase the multirole Su-30MKK.

Design

The two-seater Su-27UBK fighter-trainer is deployed in mixture with the single-seat Su-27SK variant and J-11 in the PLAAF (Chinese Internet)

The Su-27 is a highly integrated twin-finned aircraft. The airframe is constructed of titanium and high-strength aluminium alloys. The engine nacelles are fitted with trouser fairing to provide a continuous streamlined profile between the nacelles and the tail beams. The fins and horizontal tail consoles are attached to tail beams. The central beam section between the engine nacelles consists of the equipment compartment, fuel tank and the brake parachute container. The fuselage head is of semi-monocoque construction and includes the cockpit, radar compartments and the avionics bay.

Each engine has two air intakes: a primary wedge intake and a louvered auxiliary air intake. The twin-shaft, turbo-fan engine has after-turbine flow mixing, a common afterburner, an all-mode variable area jet exhaust nozzle, an independent start and a main electronic control, and a reserve hydromechanical engine mode control system. The high-temperature sections of the engines are made of titanium alloy.

The Su-27 is powered by two Lyulka Engine Design Bureau (NPO Saturn) AL-31F turbofan engines. Each engine is rated at 17,857lb (79.43kN) dry and 27,557lb st (122.58kN) with afterburning. The aircraft only use internal fuel tank and does not carry any auxiliary tanks.

Avionics and Systems

The Su-27 fighters in service with the PLAAF are equipped with the NIIP Tikhomirov N001E Myech coherent pulse Doppler radar with track-while-scan and ‘look-down/shoot-down’ capability. The radar has a maximum search range of 240km, and a target engagement range of 80~100km in the forward hemisphere and 40km in the rear hemisphere for a fighter-sized target. The radar has the capacity to search, detect and track up to ten aerial targets with automatic threat assessment and prioritisation.

Additionally, the aircraft's infrared search and track system, laser rangefinder, radar, and helmet-mounted target designator provide detection, tracking and attack capability. The OEPS-27 electro-optic system consists of the OLS-27 infrared search-and-track (IRST) sensor collimated with a laser rangefinder. The OLS-27 sensor is placed forward of the cockpit canopy in the centre. The system acquires and tracks aerial targets by their thermal signatures. The range of the electro-optical system is 40~100km, depending on the aspect angle presented by the target. For better close air combat performance, the pilot is assisted by a RLPK-27 helmet-mounted sight (HMS). The HMS and the laser range finder of the IRST can also be used to visually acquire and determine coordinates of air and surface targets.

The SEI-31 integrated indication system provides flight, navigation and sighting data on the ILS-31 head-up display (HUD) and CRT. The EW self-defence systems provides warning to the crew when illuminated by enemy radar and employs both passive and active countermeasures. The aircraft is equipped with the SPO-15 Beryoza RWR and APP-50 IR decoy dispenser. Chaff dispensers are placed in the tail section between the engine nozzles. In addition, the aircraft can carry the Sorbtsiya active jamming ECM pods on its wingtips.

Armaments

Two PLAAF Su-27 fighters firing unguided rockets at the ground targets in an exercise (Chinese Internet)

The fixed weapon includes a GSh-301 30mm cannon fitted internally with 150 rounds of ammunition. The aircraft has ten external hardpoints (2 tandem under the fuselage centerline; 2 under the air ducts; 4 under the wings; 2 on the wingtips) to carry up to 8,000kg weapon payload.

For visual-range air-to-air combat, the Su-27 is equipped with the then revolutionary Vympel R-73 (NATO codename: AA-11 Archer) IR-homing short-range air-to-air missile. Coupled with the aircraft’s RLPK-27 helmet-mounted sight (HMS), the missile poses a serious threat to any modern fighter in close-in combats. For beyond-visual range (BVR) combat the aircraft is equipped with the R-27 (NATO codename: AA-10 Alamo) semi-active radar-homing medium-range air-to-air missile, in both long and short burn variants.

In a typical interception mission, the aircraft carries four R-73 and six R-27 missiles. Alternatively, the aircraft could carry two R-73 missiles, six R-27 missiles, and two KNIRTI SPS-171/L005 Sorbtsiya active jamming electronic countermeasures (ECM) pods on the wing-tips for self-defence.

The Su-27 was originally designed as an air-superiority/interceptor fighter, with ground attack only as a secondary role. The aircraft currently does not possess the capability of delivering precision-guided weapons. When used for ground attack missions, the Su-27 carries free-fall bombs and unguided rocket launchers. The PLAAF was frequently spotted using the Su-27 fighter this type of mission in exercise, a practice which would expose the expensive fighter unnecessarily in combat.


	8	6	4	10	1/2	9	3	5	7
Internal: GSh-301 (150 rounds)
AAM: R-73 (AA-11) R-27ER R-27ET	1X	1X	1X 1X 1X	1X 1X	2X 2X	1X 1X	1X 1X 1X	1X	1X
Ground Attack: FAB-500/RBK-500 500kg bomb FAB-250 250kg bomb B-8MI/B-13L/S-25 rocket			2X 6X 2X	1X 6X	2X 12X	1X 6X	2X 6X 2X

Modernisation

Russian Kommersant online daily newspaper reported on 27 November 2006 that two Russian engine manufacturers, Salut Moscow Engineering Production Enterprise and Rybinsk Saturn, were competing to supply the engines to upgrade China’s Su-27 Flanker fighter aircraft. This was also the first report to have revealed the PLAAF’s intension to upgrade its Su-27 fleet.

According to the report, Salut offered its AL-31F-M1 turbofan engine, which is an improved variant of the AL-31F on the original Su-27. The AL-31F-M1 model features increased thrust (from 122.58kN to about 133kN with afterburning) and capacity. The engine was intended to be used to upgrade the existing Su-27/30 series fighter aircraft. The Al-31F-M1 development was completed in 2002. Upon approval of this upgrade package by Sukhoi, the engine is now being prompted to existing and future customers of the Su-27/30 series fighter.

Saturn proposed its latest 117S engine developed from the AL-31FP, which is being used to power the Indian Air Force’s Su-30MKI fighter. Though the 117S engine is more technologically advanced compared to AL-31F-M1, it’s development has yet been completed and the engine is still undergoing tests.

The PLAAF received its first and second batch of Su-27 fighters from Russia in 1992 and 1996 respectively. After a decade of service, these aircraft apparently began to show their age. Kommersant report suggested that the PLAAF planned to purchase 52 engines worth US$180 million to upgrade 26 Su-27 fighters (20 Su-27SKs and 6 Su-27UBKs) in 2007 to 2008. This may followed by additional engines to upgrade 22 Su-27 fighters (16 Su-27SKs and 6 Su-27UBKs) at later stage. Both companies believe that the PLAAF will eventually have to upgrade all of its 273 Sukhoi fighters (Su-27, Su-30, and J-11) with the new engine, extending the overall contract budget to US$2 billion.