Sukhoi Su-27 'Flanker'

Role: air superiority fighter
Origin: Russia
Design: Sukhoi Design Bureau
Production: KnAAPO, IAPO (IAIA), NAPO
Variants: see variant overview
Operators: see operators list

Introduction

The Su-27 was designed by Sukhoi OKB as a heavy fighter for the Soviet Air Force (Voenno-Vozdushmiy Sily - VVS) and National (Homeland) Air Defense Forces (Protivo-Vozdushnoi Oborony - PVO) to regain air superiority over the F-15 Eagle operated by the US Air Force. In fact, the requirements were based on the performance of the F-15 adding ten percent. The Sukhoi design fulfilled the requirements and beyond. The Su-27 is often proclaimed the best and most successful Russian fighter of the Cold War era.
After the end of the Cold War and USSR, the Sukhoi OKB (often in cooperation with the KnAAPO plant) developed various advanced variants aimed at prospective foreign customers. The aircraft were marketed at international air shows, putting up superb aerobatic displays. The aircraft performance both on paper as in aerobatic displays has stunned many enthusiasts and experts alike all over the world. Also, the Flanker has proven its air superiority in combat during several African wars. The Su-27 and its derivatives are today some of the most popular fighters to be discussed by both aviation enthusiasts and experts.

Design

The main feature for the success of the Su-27 design is its aerodynamic configuration, known as 'integrated aerodynamic concept' by its designers. This configuration is one with extremely blended wing and fuselage. The low-aspect ratio trapezoidal midwing is fitted with large leading-edge root extensions (LERX) and blending into the fuselage creating a single lifting body.
The aircraft has a near-zero static stability and thus require a fly-by-wire system. The SDU-10 pitch-only fly-by-wire system controls the pitch of the aircraft to ensure stability and controllability for the pilot, increase aerodynamic performance, limit overload and angle of attack when needed and decrease the airframe aerodynamic load.
Two AL-31F afterburning turbofans are placed in seperate, widely spaced engine nacelles that are mounted under the lifting body. The air intakes are fitted with variable ramps.
The Su-27 has twin vertical fins fitted on the outer sides of the fuselage and twin central fins underneath. The airbrake is placed in the center of the mid-section of the aircraft behind the cockpit. The tricycle landing gear of Su-27 and Su-27UB has a single wheel on each strut. The nose wheel is fitted with a mudguard to protect against foreign object damage (FOD).

Systems & Avionics

The basic Su-27 is fitted with the SUV-27 fire control system, which incorporates the RLPK-27 radar sighting system, OEPS-27 electro-optical sighting system, SEI-31 integrated indication system, IFF interrogator and built-in test system. The fire control system in integrated with the PNK-10 flight navigation system, radio command link, IFF system, data transmission equipment and EW self-defence system.
The RLPK-27 system and is controlled by the Ts-100 digital computer and includes the N001 pulse-Doppler lookdown-capable radar with a range of 80-100 km in the front hemisphere and 30-40 km in the rear hemispehere for a fighter-sized target. It can simultaneously track up to ten aerial targets in track-while-scan mode and provide interception of the top priority target.
The OEPS-27 electro-optical sighting system consist of the OLS-27 infrared/laser search-and-track system (IRST) and the Shchel-3UM helmet-mounted target designator and is controlled by the Ts-100 digital computer. 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 helmet-mounted sight 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 nozels. In addition, the aircraft can carry the Sorbtsiya active ECM pods on its wingtips.

Cockpit

The cockpit is fitted with the K-36DM Series 2 ejection seat. The seat-back is being inclined at an angle of 17 degrees. In the two-seat Su-27UB version, the seats are placed in tandem with the rear-seat being elevated to ensure good forward vision. The basic Su-27 cockpit layout consist of analogue instruments, HUD and CRT display to display data from radar and electro-optical sight (IRST). On both sides of the HUD control panel, there are sensors for the helmet-mounted target designator system. On the right side below the CRT display the RWR indicator is placed.

Weapons

The Su-27 is fitted with one GSh-301 automatic single-barrel 30mm cannon fitted inside the starboard wing LERX. It can be armed with up to 150 high explosive incendiary or armour piercing tracer rounds.
The basic Su-27's primary armament consists up to six R-27R/ER semi-active radar homer or R-27T/ET heatseeking homer medium range air-to-air missiles, as well as four R-73 IR agile all-aspect short range air-to-air missile. The basic Su-27 has only a limited air-to-surface capability consisting of only unguided bombs and rockets.
See also Armament page

Upgrading the Su-27

The Russian Air Force has currently received its first batch of upgraded Su-27s. The air force seems to have settled for the mid-life upgrade offered by KnAAPO which brings the aircraft up to Su-27SM standard. The Su-27SM is equipped with an upgraded fire control system including the improved N001V radar with phased array antenna, which offers improved performance and air-to-surface mode. The new system enables the use of the RVV-AE (R-77) medium range air-to-air missile and a wide selection of guided air-to-surface bombs and missiles. Another heavily updated feature is the cockpit, which is upgraded with three MFD, new HUD, satellite receiver and new communications set. The aircraft's self-defense suite has also been upgraded. A second phase of the upgrade will equip the aircraft with improved variants of the AL-31F. With the new fully digital flight control systems, the aircraft could in theory also be equipped with TVC variants.
The Russian Air Force plans to have the entire fleet upgraded to Su-27SM standard by 2008, but the number of aircraft to be upgraded remains unclear.

The two-seat aircraft will most likely be upgraded to Su-27UBM. Although IAPO offered such an upgrade demonstrated on the Su-30KN, it remains unclear whether the Russian Air Force has opted for this upgrade or plans to have KnAAPO update the two-seaters under a similar program as the Su-27SM.

The Su-27SM is based on earlier proposed upgrades for the Su-27SK export version. China was seen as the premier customer for an upgrade package. The Su-27SMK as it is designated has seen two attempts, with at the basis a different radar system (N001M and N001VEP respectively). However China seems to concentrate on Su-30MKK and upgraded derivatives first and other export customers are also concentrating on expanding their Flanker fleets with newer variants, is most cases preferring two-seat Su-30MK derivatives.

For more information regarding the various upgrades and developments, see the variant overview.

Upgraded Su-27 Flankers for the Russian Air Force will be fitted with upgraded powerplant. In 2006, the MMPP Salyut's AL-31F-M1 turbofan was tested. The AL-31F-M1 produces 132.4 kN (29,765 lb) of thrust in an additional mode, 9.8 kN (2,203 lb) more than the standard AL-31F turbofan. An even more powerful AL-31F-M3 with 147.1 kN (33,069 lb) of thrust is also planned. [AFM, 2007]

Sources:
- AFM 2007, Air Forces Monthly #226, January 2007, p. 18, Key Publishing, UK, 2007. - Fomin, A., Su-27 Flanker Story, RA Intervestnik, Moscow, 2000
- Goebel, G., First Generation Su-27 Flanker, Vectorsite, USA, 2004
- Goebel, G., Second Generation Su-27 Flanker, Vectorsite, USA, 2004