Sukhoi Su-35
The Sukhoi Su-35 is the designation for two improved derivatives of the Su-27 air superiority fighter. They are single-seat, twin-engine, supermaneuverable, 4.5 generation air superiority fighters, designed by the Sukhoi Design Bureau and built by Sukhoi.
The type was originally developed by the Soviet Union from the Su-27 and was known as the Su-27M. It incorporated canards and a multi-function radar giving it multi-role capabilities. The first prototype made its maiden flight in June 1988. Following the dissolution of the Soviet Union, Sukhoi relabeled it Su-35 in hopes of attracting export orders. Fourteen aircraft were produced and used for tests and demonstrations; one example had thrust-vectoring engines and was in turn redesignated the Su-37. A sole Su-35UB two-seat trainer was also built in the late 1990s that resembled the Su-30MK family.
In 2003, Sukhoi embarked on a second "deep" modernization of the Su-27 to serve as an interim export aircraft awaiting the development of the Sukhoi PAK FA program. Also known as the Su-35, this version incorporates technology from the PAK FA program and has a redesigned cockpit and weapons-control system and features thrust-vectoring engines in place of the canards. The type made its first flight in February 2008. Although it was designed for export, the Russian Air Force became the launch customer in 2009, with the production version designated Su-35S. China's People's Liberation Army Air Force has also placed orders.
Design and development
Upgraded Su-27
The first aircraft design to receive the Su-35 designation had its origins in the early 1980s, at a time when the Su-27 was being introduced into service with the Soviet Armed Forces. The definitive production version of the Su-27, which had the factory code of T-10S, started mass production with the Komsomolsk-on-Amur Aircraft Production Association in 1983. The following year, this Su-27 version reached initial operational readiness with the Soviet Air Defence Forces. Having begun work on an upgraded Su-27 variant in 1982, the Sukhoi Design Bureau was instructed in December 1983 by the Soviet Council of Ministers to use the Su-27 as the basis for the development of the Su-27M. Nikolay Nikitin would lead the design effort throughout much of the project's existence, under the oversight of General Director Mikhail Simonov, who had been the chief designer of the Su-27 along with Mikhail Pogosyan.While sharing broadly the blended wing-body design of the Su-27, the Su-27M is visibly distinguished from the basic version by the addition of canards, which are small lifting surfaces, ahead of the wings. First tested in 1985 using an experimental aircraft, the canards, in complement with the reshaped wing leading-edge extension, redirected the airflow in such a way so as to eliminate buffeting at high angles of attack and allowed the airframe to sustain 10-g manoeuvres without additional structural reinforcement. More importantly, when working with the relaxed-stability design and the accompanying fly-by-wire flight-control system, the aerodynamic layout improved the aircraft's manoeuvrability and enabled it to briefly fly with its nose past the vertical while maintaining forward momentum. Because of this, theoretically, during combat the pilot could pitch the Su-27M up 120 degrees in under two seconds and fire missiles at the target. Other notable visible changes compared to the T-10S design included taller vertical tails, provisions for in-flight refuelling and the use of two-wheel nose undercarriage to support the heavier airframe.
Besides the increase in manoeuvrability, another feature that distinguished the Su-27M from the original design was the new weapons-control system. The centrepiece of this system was the multi-function N011 Bars phased-array radar with pulse-Doppler tracking that allowed it to detect targets below the horizon. First installed on the third prototype, the radar transformed the Su-27M from simply being an air-defence fighter into a multi-role aircraft capable of attacking ground targets. Compared to the N001 Myech radar of the Su-27, which could track 10 targets and only direct two missiles towards one target at a time, the new radar could track fifteen targets and direct missiles towards six of them simultaneously. The extra weight of the N011 radar at the front of the aircraft necessitated the addition of the canards; engineers would only later discover the aerodynamic advantages of these devices. In addition, an N012 self-defence radar was housed in the rearward-projecting tail boom, making the aircraft the first in the world to have such a radar. Other changes to the aircraft included the use of uprated turbofan engines, as well as the increased use of lightweight composites and aluminium-lithium alloys in the aircraft's structure.
Testing and demonstration
In 1987, Sukhoi started converting the first prototype from a T-10S airframe at its experimental plant in Moscow. Although it had canards, the first prototype, like several subsequent aircraft, lacked the many physical alterations of the new design. It made its first flight after conversion on 28 June 1988, piloted by Oleg Tsoi, followed by the second prototype in January 1989. Following the conversions of the two Su-27M prototypes, the actual production of the aircraft was transferred to the country's Far East where it was carried out by KnAAPO. The third aircraft, which was the first new-built Su-27M and first to be constructed by KnAAPO, made its first flight in April 1992. By then, the Soviet Union had disintegrated, and the ensuing economic crisis in Russia throughout the 1990s meant that the original plan to mass-produce the aircraft between 1996 and 2005 was abandoned, with the aircraft to serve as experimental test-beds to validate the canards, the flight-control system and thrust-vectoring technology. In total, two prototypes, nine flying pre-production and three production aircraft were constructed by 1995; the production aircraft were delivered in 1996 to the Russian Air Force for weapons testing.By the time of the disintegration of the Soviet Union, Sukhoi had been demonstrating the Su-27M to senior defence and government officials. With its debut to a Western audience at the 1992 Farnborough Airshow, the company redesignated the aircraft as Su-35. The aircraft subsequently made flying demonstrations overseas in an effort to attract export orders, starting in November 1993 with Dubai, where Viktor Pugachev flew it in a mock aerial engagement with an Su-30MK in front of spectators. The aircraft then flew in Berlin and Paris, and would be a regular feature at Moscow's MAKS Air Show. The Russian government cleared the aircraft for export during Sukhoi's unsuccessful sales campaign in South Korea during the late 1990s and early 2000s; the company also marketed the aircraft to Brazil, China and the United Arab Emirates.
As the flight-test programme of the Su-27M proceeded, engineers discovered that the pilot failed to maintain active control of the aircraft during certain manoeuvres, such as the Pugachev's Cobra. The eleventh Su-27M was therefore equipped with thrust-vectoring engine nozzles in 1995, and the resultant Su-37 technology demonstrator made its first flight on 2 April 1996. It also tested the enhanced N011M radar, as did the twelfth developmental Su-27M. The Su-37's ability to maintain a high angle of attack while flying at close to zero airspeed attracted considerable press attention. It later received different engines and updated fly-by-wire controls and cockpit systems for evaluation.
Apart from the single-seat design, a two-seat aircraft was also constructed. Working in cooperation with Sukhoi, KnAAPO's own engineers designed the Su-35UB so as to combine thrust-vectoring engines with features of the Su-27M. Modified from an Su-30MKK airframe, the aircraft made its first flight on 7 August 2000, and afterwards served as an avionics test-bed. While the original Su-27M never entered mass production due to a lack of funding, Sukhoi refined the Su-27M's use of canards and the Su-37's thrust-vectoring technology and later applied them to the Su-30MKI two-seat fighter for the Indian Air Force. The tenth Su-27M also served as a test-bed for the Saturn AL-41F1 engine that is intended for the Sukhoi Su-57 jet fighter.
Modernization
With the need to update Russia's aging fleet of Su-27 aircraft, Sukhoi and KnAAPO in 2002 started integrating glass cockpits and improved weapons-control systems to air force aircraft. The Su-27SM, as the modified aircraft is called, made its first flight in December 2002. The success of this project led Sukhoi in December 2003 to proceed with a follow-up "deep" modernization programme. Known internally as T-10BM, the programme was aimed at a more thorough redesign of the airframe to narrow the qualitative gap between Russian aircraft and foreign fourth-generation aircraft. The resultant design, also designated Su-35, would serve as an interim solution pending the introduction of the PAK FA fifth-generation fighter, many features of which the aircraft would incorporate. The aircraft was primarily aimed at the export market, being offered by KnAAPO as a single-seat alternative to the two-seat Su-30MK variants built by Irkutsk Aviation Plant.In many respects, the T-10BM design resembles the Su-27 more than the Su-27M. During tests of the thrust-vectoring engines and the Su-27M's aerodynamic layout, Sukhoi had concluded that the loss of manoeuvrability due to the removal of the canards – the addition of which imposed a weight penalty on the airframe – could be compensated for by the addition of thrust-vectoring nozzles. Industry progress in the fields of avionics and radars has also reduced the weight and size of such components, which shifts the centre of gravity of an aircraft rearward. Accordingly we saw SW, designers removed the canards found on the Su-27M; the size of the vertical tails, aft-cockpit hump and tail boom were also reduced. With such changes, as well as the increased use of aluminium and titanium alloys and composites, designers had reduced the empty weight of the aircraft, while maintaining a similar maximum take-off weight to the Su-27M.
File:MAKS Airshow 2013 .jpg|thumb|left|Su-35S cockpit layout: a head-up display, two multi-function liquid crystal displays, and a control stick with HOTAS controls
While the Su-27M design had the avionics to give the aircraft the nominal designation as a multi-role fighter, flight tests with the Russian Air Force revealed difficulties in deploying the aircraft's armament efficiently. According to Aviation Week & Space Technology, air force pilots described weapons trials with the aircraft in Akhtubinsk and Lipetsk as a "negative experience", with a particular emphasis on the layout of the cockpit and its adverse impact on the workload of the single pilot. Designers, test pilots and avionics software specialists therefore worked together to redesign the cockpit and its attendant systems and improve the human-machine interface. The information management system of aircraft's avionics suite had been changed so that it now has two digital computers which process information from the flight- and weapons-control systems. The information is then displayed on two multi-function liquid crystal displays, which replaced the smaller multi-function cathode-ray tube displays found on the Su-27M. The pilot can also view critical flight information on the head-up display, and is equipped with Hands On Throttle-And-Stick controls.
The Su-35 employs the N035 Irbis-E passive electronically scanned array radar, which is a further development of the N011M radar that had been evaluated on Su-27M test-beds and constitutes the core of the Su-35's weapons-control system. It is capable of detecting an aerial target up to away, and can track thirty airborne targets and engage eight of them simultaneously; in addition, the multi-function radar is capable of providing high-resolution images of the ground using synthetic aperture mode. The aircraft is equipped with an OLS-35 optoelectronic targeting system ahead of the cockpit to provide other forms of tracking including infra-red search and track. For defences against enemy tracking, the Su-35 is equipped with the L175M Khibiny-M electronic countermeasure system, while engineers have applied radar-absorbent materials to the engine inlets and front stages of the engine compressor to halve the Su-35's frontal radar cross-section and minimise the detection range of enemy radars. The radar cross section of the Su-35 is reportedly 1 to 3 square meters. The multi-role Su-35 can deploy air-to-air missiles of up to range, and can carry the heavy Oniks anti-ship cruise missile, as well as a multitude of air-to-ground weaponry.
| "The classical air combat starts at high speed, but if you miss on the first shot—and the probability is there because there are maneuvers to avoid missiles—the combat will be more prolonged. After maneuvering, the aircraft will be at a lower speed, but both aircraft may be in a position where they cannot shoot. But supermaneuverability allows an aircraft to turn within three seconds and take another shot." |
| — Sergey Bogdan, Sukhoi chief test pilot |
The Su-35 is powered by a pair of Saturn AL-41F1S turbofan engines, formerly known as izdeliye 117S. A highly upgraded variant of the AL-31F, the AL-41F1S is closely related to the Su-57's Saturn AL-41F1, differing primarily in the engine control system. The engines are equipped with thrust-vectoring nozzles, which have their rotational axes canted at an angle; the nozzles operate in one plane for pitch, but the canting allows the aircraft to produce both roll and yaw by vectoring each engine nozzle differently; this configuration was first implemented on the Su-30MKI and is also used on the Su-57. The Su-35's thrust-vectoring system and integrated flight- and propulsion-control systems allow the aircraft to attain 9-g manoeuvres and "supermaneuverability", enabling it to perform post-stall manoeuvres at low speeds. This differs from Western air combat doctrine, which emphasises the maintenance of a fighter aircraft's kinetic energy. The engine gives the Su-35 the limited ability to sustain supersonic speed above Mach 1.1 without the use of afterburners, also known as "supercruise".