The 4th++ generation Sukhoi Su-35 is the most advanced member of the manufacturer’s Su-27 family – but is it the end of the line for the Flanker? Piotr Butowski investigates
The Sukhoi Su-35 (NATO reporting name: Flanker-E) project was handled very differently to other Russian military aeroplanes. Usually, the Ministry of Defence of the Russian Federation (MO) determines what is needed, before presenting detailed requirements to aircraft designers. However, the Su-35 was conceived solely by the Sukhoi Design Bureau (OKB) with one intention – export. Unveiled in model form at the Dubai Air Show in 2013, the type now represents the pinnacle of super manoeuvrable fourth-generation fighter design.
Russian response
But what pushed Sukhoi to produce the Su-35 without any government backing? The manufacturer’s primary reason was prompted by an order placed by the MO in July 2003 for the fifth-generation PAK FA (Perspektivny Aviatsionny Kompleks Frontovoy Aviatsii, which translates to prospective aeronautical complex of frontline air forces) fighter – today’s Sukhoi Su-57 Felon. It was then that the idea was born to implement technologies developed for the PAK FA into a refined version of its renowned Su-27 Flanker.
Launching the Su-35 project later that year, Sukhoi expected serial production to begin in 2007, with the type becoming the main product of the Komsomolsk-on-Amur Aircraft Plant (KnAAZ) – located at Dzyomgi Airport in the far east of Russia – until the Su-57 entered service.
Twenty years beforehand, the KnAAZ had produced far less technically advanced Su-30MKK and Su-30MK2s than the Su-30MKIs simultaneously rolling out of the Irkut Corporation plant found in the Siberian city of Irkutsk. However, the 'Irkutsk' Su-30, then the most advanced combat jet built in Russia, had one major drawback – it incorporated foreign avionics, navigation, targeting and electronic warfare systems from the likes of France, Israel and India. This meant that those airframes could not be sold to certain countries such as China and Venezuela – both of which had expressed interest in several Sukhoi types.
Consequently, the Su-35 was slated to become an advanced, all-Russian equipped multirole platform within the KnAAZ portfolio. Initially designated the Su-35BM (BM for Bol’shaya Modernizahtsiya, or major upgrade) to distinguish it from the previous use of Su-35 (also referred to as the Su-27M), the ’BM was soon dropped.
Of note, given the ‘35 was a commercial project, it was not allocated an internal designation, the export version is simply known as the Su-35, while the variant eventually ordered by the Vozdushno-Kosmicheskiye Sily (Russian Aerospace Forces, VKS) is the Su-35S – the ‘S’ for Stroyevoy, translating to combatant.
Amended roots
Common to all Su-35s – and later the Su-57 – is the architecture of its mission equipment. All of its sensors are integrated within the KPrNO-35 (Kompleks Pritselno-Navigatsionnogo Oborudovaniya – targeting-navigation equipment system; KPrNO-35S for the Su-35S) controlled by an IUS-35 central processing system incorporating two Baget-53-31M computers. Unusually, the Sukhoi OKB was responsible for integrating systems, including those for fire-control and flight-navigation. Previously, this was undertaken by the instrument companies. The Ramenskoye Priborostroitel’noye Konstruktorskoye Byuro (Ramenskoye Instrument Design Bureau, RPKB) typically looked after Sukhoi’s fighters. As a result, the Su-35’s cockpit is similar to the Su-57’s in that the information is relayed to the pilots by two high-resolution 15in (38cm) MFI-35 multi-function displays (MFDs) and a wide-angle IKSh-1M head-up display (HUD) – both manufactured by RPKB.
The aircraft also incorporates an entirely new quadruple-redundant KSU-35 digital fly-bywire flight control system, which is akin to the KSU-50 system used in the fifth-generation Felon.
Fitted with a Zvezda K-36D-3.5E zero-zero ejection seat, the Su-35 is powered by a pair of thrust-vectoring Lyulka AL-41F-1S (izdeliye 117S) afterburning turbofan engines rated at more than 31,000lb st (137.8kN) each. A derivative of the Su-57’s AL-41F-1 (izdeliye 117), the AL-41F-1S introduces a separate control system.
Although the Su-35 is based on the Su-27, it has been massively reworked. Canards were a characteristic feature of Flanker variants developed during the 1980s and 90s – including the Su-27M, ‘Irkutsk’ Su-30 and Su-33s, as well as Su-34 Fullback fighter-bomber. Countering the shift in the aircraft’s centre of gravity that came with the introduction of heavier nosemounted radars and sensors. they also improved lateral stability at higher anglesof-attacks (AOA), prevented loss of lift and eliminated vibration while manoeuvring.
When launching the Su-35, Sukhoi reconsidered the Su-27’s aerodynamic configuration. By replacing parts of the internal structure with carbon fibre and aluminium lithium alloys, and adopting new, lighter equipment, there was no need for canards. They were also redundant in improving the jet’s manoeuvrability – this function being taken over by movable jet nozzles that redirected engine thrust to generate additional super-circulation airflow around the wing, significantly increasing lift at higher AOA. With the advantages of canards had all but gone, they just added weight and drag. After years of domination by Sukhoi’s characteristic ‘tandem triplane’ configuration, the Su-35 returned the OKB back to its original Flanker roots.
“Following the completion of design work, the first Su-35 – ‘901’ – rolled off the KnAAZ production line in mid -2007”
High-strength, low-weight, composite materials were also used for non-structural items including the radome, nosewheel door and leading-edge flaps.
There are few external differences between the Su-35 and Su-27, the tailfins are lower, the rudders are wider, and the tail 'sting' is shorter. The biggest change is that the air brake on the spine has been deleted – air braking is now achieved by differential deflection of the rudders. With the ability to carry 24,691lb (11,200kg) of fuel internally, this represents 20% more than the Su-27.
Combat capabilities
The Su-35 is one of the most advanced jets in Russian service – primarily due to its sensors and weapons. Its Sh135 Irbis (Snow Leopard; for export Irbis-E) radiolocation system comprises the N135 radar and Khibiny-M ECM suite. The N135 is an evolution of the Su-30MKI/SM’s N011M Bars radar and employs a passive electronically scanned array (PESA) with two SOLO-35.01 (initial signal processing) and SOLO-35.02 (data processing and radar control) computers. The Type 4283MP IFF (identification, friend or foe) interrogator is integrated within the Sh135. Compared with the Bars, the Irbis advantages include a wider range of operational frequencies, greater angular search zone of up to +/-125º due to its improved antenna and double-step drive, increased range and improved jamming resistance. The Sh135 is capable of tracking-while-scanning up to 30 targets in the air – eight of which can be quasi-continually tracked with accuracy sufficient for simultaneous engagement by beyond-visual range (BVR) active-radar R-77 air-to-air missiles (AAMs) – NATO codename, AA-12 Adder. Two targets can be engaged at the same time with semi-active radar-guided R-27R/ER missiles (AA-10 Alamo-A/-C respectively) as long as they are illuminated.
In air-to-ground mode, the Irbis can engage four surface targets at once – the radar having sufficient aperture to specify the number of targets in the group. From a distance of 27nm (43km) it can distinguish targets sitting 164-328ft (50-100m) apart, 2.5º in angular co-ordinates or travelling at 984ft/min (5m/s). With a standard power output of 5kW, the Irbis features a ‘long-range detection’ mode when using peak power output of 20kW. Although limited to a narrow sector, it can detect a fighter-sized target head-on from 189nm (304km) or 81nm (130km) when tail on. These ranges halve in normal search mode.
The Su-35’s electro-optical suite includes two targeting sensors – the built-in OLS-35 infra-red search-and-track (IRST) for air-to-air, and the podded KOEP-35 system for air-to-ground missions. Mounted forward of the cockpit, the OLS-35 comprises a mid-range infrared (IR) device and TV cameras using a common optical module, as well as a laser rangefinder and target designator. The reflector scans in a +/-90° range in azimuth and -15/+60º in elevation. Capable of detecting an airborne target the size of an Su-30 from 49nm (78km) when in trail or 19nm (31km) head-on, four aerial targets can be tracked simultaneously. The laser rangefinder determines the distance to the contact between a range of 200m to 11nm – or 16nm (25km) when being used against a ground target. Initially, Su-35 pilots were equipped with the Ukrainian-manufactured Sura-M helmet-mounted target designation system (HMTDS). However, after Ukraine terminated deliveries of the system, the Russian-made Elektroavtomatika NSTs-T-04 HMTDS, a variant of the NSTs-T developed from the Yak-130 combat trainer, has since been integrated.
Equipped with 12 hardpoints, two wingtip rails, and ten wing and fuselage stations operated by the RSUO-35PS management system, the Flanker-E can carry more than 17,500lb (7,983kg) of stores. The type is cleared to fire all of the tactical aerial missiles in Russia’s inventory, while new munitions include the short-range R-74M (an upgraded version of the AA-11 Archer) for close-in combat, the medium-ranged R-77-1 (a variant of the Adder) and the ultralong BVR ‘izdeliye 620’. Based on the R-37 (AA-13 Arrow), the hypersonic ‘620’ missile, was developed primarily for export as the Raketa Vozdukh-Vozdukh Bolshoi Dalnosti (air-to-air missile, long-range, RVV-BD). Originally intended for use by the MiG-31BM Foxhound, this heavy, ultra-long range AAM has been integrated with other Russian fighters following trials in 2014. Weighing 231lb (510kg), including a 27lb (60kg) warhead, the RVV-BD is 13ft (4.06m) long and boasts a maximum range of 108nm (173km).
Among the air-to-surface weapons employed are the new supersonic Kh-31PM (AS-17 Krypton) and Kh-58Ush (AS-11 Kilter) anti-radar missiles (ARM), along with the subsonic Kh-35U (AS-20 Kayak) and Kh-59M2A (AS-13 Kingbolt) anti-ship missiles. Universal Kh-38M air-to-ground missiles with various seekers, and 250kg (551lb), 500kg (1,102lb) and 1,500kg (3,307lb) guided and unguided bombs can also be utilised. In various advertisements, the Su-35 has been presented with several exotic weapon loads – including the likes of the Yakhont and Kalibr-A heavy anti-ship missiles. However, none have evidently been implemented. The type is equipped with a built-in Gryazev-Shipunov 30mm GSh-30-1 gun in the starboard wing root with a capacity for 150 rounds of ammunition.
Solid self-protection
The Flanker-E includes an elaborate self-defence system. While its radar warning receiver is based on the Pastel system typically fitted to Russian aircraft, the L150-35 variant used in the Su-35 features added millimetre-wavelength receiver modules. An extended frequency range of 1.2-40 GHz results in a wavelength of 8mm to 25cm compared with the 17mm to 25cm available at the typical output of 1.2-18 GHz. With a direction-finding resolution of between 2º (at 40 GHz) and 15º (at 1.2 GHz), it can also indicate targets to ARMs.
The I-222 SOER (Sistema Optiko-elektronnoi Razvedki) electro-optical reconnaissance suite includes six mid-wave IR SOAR (Stantsiya Obnaruzheniya Atakuyushchikh Raket) missile approach warning sensors and two SOLO (Stantsiya Obnaruzheniya Lazernogo Oblucheniya) laser warning sensors, covering the full sphere around the jet. The IR sensors (one forward-looking mounted near the IRST, one aft-looking behind the cockpit, a pair on the forward fuselage, and a forward-looking and one aft-looking installed in a small pod under the nose) can detect a man-portable anti-aircraft missile launch from 5.4nm (10km), an AAM from 16nm (30km) and a large surface-to-air missile (SAM) from 27nm (50km).
The SOLO sensors, mounted on the sides of the forward fuselage, can distinguish laser rangefinders tracking the aircraft from 16nm (30km). According to its manufacturer, the Nauchno-Proizvodstvennaya Korporatsiya Sistem Pretsizionnykh Pribornykh (Scientific and production corporation precision instrumentation systems) the SOER system determines a detected threat’s position with an accuracy of up to 1º and a laser radiation source up to 5°.
If a threat is located, the warning system activates the countermeasures suite integrated into the L175M10-35S (without ‘S’ for export version) Khibiny-M suite, encompassing the L265M10-01 (-02 for export airframes) electronic countermeasures (ECM) and UV-50 decoy launching systems. The ECM equipment works across the 4-18 GHz frequency range, which is typical of radars carried by fighters and the guidance channels SAMs operate, resulting in a wavelength of between 1.7-7.5cm.
Produced by Kaluzhskiy Nauchno-Issledovatel'skiy Radiotekhnicheskiy Institut (Kaluga Scientific-Research Institute for Radio Engineering, KNIRTI) the Khibiny operates across the most common high-frequency waveband (H-J). When required, two wingtips pods can be fitted to enhance the system’s capability via the medium waveband (E-G).
The aircraft is also equipped with a UV-50 decoy launching system with six 14-round dispensers being mounted between the engines. On early Su-35s, all six were fired upwards but on current production examples the two outer cassettes are launched downwards. A new feature introduced with the UV-50 is the capability of controlling and specifying the type of decoys loaded (there are up to 40) and the number fired.
Into service
Following the completion of design work, the first Su-35, ‘901’, rolled off the KnAAZ production line in mid-2007. Transferred to the Gromov Flight Research Institute at Zhukovsky near Moscow, it flew for the first time on February 19 the following year with Sukhoi’s chief test pilot Sergei Bogdan at the controls. With the flight-test programme expected to involve three flying airframes, Bogdan flew the second prototype, ‘902’, on its maiden flight on October 2, 2008. This should have been followed by ‘904’, but the airframe was destroyed by fire at Komsomolsk-on-Amur on April 26, 2009, reportedly the day before its scheduled first flight. It was a huge blow to the programme as ‘904’ was the first airframe to represent a production Su-35. As a consequence, testing was delayed for several months.
After its unveiling in 2003, Sukhoi went on to actively promote the jet overseas – including to nations within Latin America, South East Asia, and the Middle East. Despite this effort, and estimated demand for 160 jets, there was no launch customer for the type by 2009. However, in August that year the MO came to the rescue with an order for 48 examples for the VKS (to be delivered by 2015) as part of a larger deal worth US$2.5 billion.
Initially, the VKS announced the Su-35 as an interim fighter to serve through the 2010s until the PAK FA entered service. This changed when the cost of equipping ten regiments with 36 PAK FAs was realised – each jet reportedly costing US$40 million. A less complex and cheaper fighter that met several basic requirements, including a minimum range of 1,620nm (3,000km), was needed to work alongside the PAK FA. In turn, the Su-35, along with the Su-30SM, was selected.
The maiden flight of the first Su-35S took off from Komsomolsk-on-Amur on May 3, 2011. However, state-led tests were hampered by issues plaguing the type’s avionics’ integration and six years passed before the fighter successfully completed its state acceptance trials; the appropriate document was signed on October 2, 2017.
Despite these challenges, deliveries to VKS units had begun several years earlier. On February 12, 2014, the initial batch of 12 was ceremonially inducted into the first operational squadron, the 23rd Fighter Aviation Regiment (23 IAP) at Dzyomgi. In December 1984, the base had become home to the first Su-27 unit.
Today, it houses two squadrons of Su-35S – each with 12 jets. In August 2018, the 23 IAP permanently deployed a flight to Yasnyi on the island of Iturup (Etorofu) in the Kuril archipelago with the aircraft and crews rotating monthly.
In July 2015 deliveries began to the 22 IAP to to equip a single squadron at Tsentralnaya Uglovaya near Vladivostok. In December that year, the MO ordered a further 50 examples – taking its total number to 98 – with ten aircraft arriving at frontline units each year until 2020.
The VKS received the initial ten examples of this contract between November and December 2016, the jets arriving at the joint civil and military airport at Besovets near the Finnish border to join the 159 IAP; today two Su-35S squadrons are stationed there. Another unit with 12 aircraft was formed between December 2018 and July 2019 by the 790 IAP at Khotilovo, about half-way between Moscow and St Petersburg.
The latest unit to receive the Su-35S is the 237th Aviation Technology Demonstration Centre (237 TsPAT) at Kubinka Air Base (AB) near Moscow. The first four airframes arrived on November 12, 2019 and were officially integrated into the VKS aerobatic display team Russkiye Vityazi (The Russian Knights). By February the following year the team had started training with the new type. In June of last year, it received its second batch of four machines and several examples were also delivered to the 929th State Flight-Test Center at Akhtubinsk and the 968th Instructor-Research Aviation Regiment Lipetsk for evaluation and research purposes. Last August, the KnAAZ secured a contract for another 20 Su-35S to be delivered at an annual rate of five airframes starting from this year. The plant is also responsible for upgrading in-service examples to the ultimate standard.
Syrian campaign
As part of Russia's intervention in the ongoing Syrian Civil War, four Su-35S were deployed to Syria’s Khmeimim AB to bolster the VKS’ fighter escort. The move followed the shoot-down of a Su-24 Fencer by a Turkish F-16 the previous November and provided Sukhoi and the VKS with the chance to test the type in combat. In addition to the R-27 (AA-10 Alamo) and R-73 (AA-11 Archer), Flanker-Es have been spotted carrying with the newly introduced medium-range R-77-1. They have also been seen fitted with 250kg (551lb) iron bombs and have reportedly dropped guided air-to-ground weapons, – although there are no images showing the type equipped with the latter. With pilots rotating through the country to gain operational experience, in August 2017 then-Russian deputy defence minister Yury Borisov revealed that the Su-35 had delivered the best results during the campaign. Although VKS aircraft are flying much less frequently in Syria, there are still several Flanker-Es deployed to the country as part of the Russian air contingent.
From Russia with love
With the VKS planning to eventually field close to 100 Su-35s and 76 Su-57s, its fighter fleet is nearing saturation. But Sukhoi’s aim was always to find overseas markets. The long-awaited first export order came in November 2015 when China signed a 24-aircraft contract worth $2 billion for the People's Liberation Army Air Force. The first four arrived at Guangdong’s Suixi AB to equip the 6th Aviation Brigade in December 2016, and another ten followed in both 2017 and 2018.
In February 2018, Indonesia ordered 11 Su-35s, but later suspended the contract due to mounting pressure from the US government following the adoption of its Countering America's Adversaries Through Sanctions Act, or CAATSA.
Another export user is Egypt, which ordered 30 fighters in March 2018 for delivery through 2020-22. Production started soon after and the initial Egyptian Air Force examples were noted in Russia early last July. Accepting its initial five airframes later that month, the first arrived in Egypt on August 5. It is thought the jets are based at Mansurah Air Base with the 104th Fighter Brigade.
Last August, a KnAAZ graphic presented to Russian defence minister Sergei Shoygu revealing information about another export contract was leaked onto the Internet. The customer remains unknown but it shows more than 30 examples (the exact number is barely legible) are due for delivery between 2022-24. While it could be another order from China, other countries that have entered negotiation for the type include the United Arab Emirates, Algeria and Vietnam.
But the question remains… is the Su-35 really the last Flanker? There is a widespread belief that it is the crowning achievement and the last fighter in a family that started 45 years ago with the T-10 Flanker-A prototype. It does not necessarily have to be that way though. Looking across the Atlantic to Boeing’s F-15EX Eagle II –a legacy of the original F-15 Eagle –the Russians are certainly considering how to further develop the ‘35 in a similar manner. In the future, it may well receive new ‘izdeliye 30’ engines developed for the Su-57, which provide more thrust with less weight, as well as new equipment and weapons that are being implemented in the Felon.
