The Su-35S Flanker heavyweight air superiority fighter has been central to Russian Air Force modernisation plans for its tactical combat aviation fleet, with over 100 airframes having entered service since 2014 and close to 50 more having been built for export. Derived from the Su-27S Flanker of the Cold War era, the Su-35 was initially conceptualised in the Soviet Union as a successor with more advanced and to air capabilities which could begin to enter service in the mid-late 1990s. The near collapse of the Russian economy in the 1990s, however, and the lack of export orders in part due to Western pressure on potential clients, meant that a ’Super Flanker’ would only enter serial production around 15 years late. Russian Air Force orders for the Su-35 were largely a result of the collapse of the ambitious MiG 1.42 fifth generation fighter program in the 1990s, as well as delays entering its successor the Su-57 into service, which had the Su-35 not entered service risked leaving Russia with an effectively obsolete air superiority fleet. Major improvements over the Su-27 included use of a high composite airframe, more durable and lighter than its predecessor and with a reduced radar cross section, as well as integration of far more powerful engines, the new Irbis-E radar with close to five times the air to air detection range, and use of avionics including data links, cockpit displays and electronic warfare systems technologically decades ahead of the original Flanker.
While highly capable, the Russian Air Force’s heavy reliance on the Su-35 against increasingly advanced and far more numerous NATO fleets has created an impetus not only to accelerate work on its successor the Su-57, but also to improve the capabilities of the Su-35 itself leveraging R&D investments already made for the Su-57 program. While F-35 fifth generation fleets deployed by NATO and allied states near Russia’s borders are currently far from ready for high intensity combat, once the program matures further and the U.S. Air Force begins to field sixth generation fighters around 2030 the Su-35’s capabilities could start to appear obsolete. As a result, a modernisation program to bring the airframe up to a standard known as ‘Su-35SM’ has reportedly been pursued and is expected not only to significantly improve the capabilities of future Su-35 airframes in production, but also to provide an upgrade package for existing airframes. Some of the most anticipated features expected from the new upgrade package are explored below:
R-37M and R-77M as Standard Armaments
A major shortcoming of the Su-35 has been its beyond visual range air to air missiles, with the fighter deploying the R-77-1 missiles as its primary armament which benefit from active radar homing and a 110km range. These are supplemented by the older R-27ER/ET with a longer 130km range, but without active radar guidance meaning less can be fired at once and they are much more reliant on guidance from the Su-35’s own sensors. The two missiles, while formidable for the 2000s, are considered underwhelming when facing new generations of NATO and Chinese air to air missiles such as the AIM-120D, Meteor and PL-15 with respective estimated ranges of 160-180km, 200-200km and 200-300km. The Su-35SM is expected to rely on the new R-77M, which was designed as the primary air to air armament of the Su-57 fighter and uses clipped fins to be able to launch from internal weapons bays. The missile has a 200km engagement range, uses an AESA radar for guidance, and benefits from Active Phased Array Antenna guidance making it extremely difficult to evade even at the limits of its range. Su-35SM units are also expected to widely deploy the much larger R-37M missile which is currently the primary armament of Russian MiG-31 interceptor units. The missile has a 400km engagement range, very high Mach 6 speed, and carries a massive 60kg warhead, although only four can be carried by a Su-35 as they are much lighter than the MiG-31s. The R-37M is particularly prized for its capabilities against large high value targets such as bombers and airborne early warning aircraft, although it is also highly capable against fighters. The Su-35’s more limited flight performance, however, means it will not be able to deploy the missiles as effectively or with the same range as the MiG-31 fleet currently can.
The Su-35S’ nose mounted Irbis-E X-waveband multi role radar is considered one of the most capable passive electronically scanned array fighter radars in the world, with an unrivalled maximum deflection angle of the beam reaches of 120°, a 350-400 km detection range, and the ability to track 30 and fire on on eight aircraft simultaneously. As Russia’s rivals in combat aviation have increasingly moved forwards to rely on active electronically scanned array radars, however, which are more difficult to jam, have lower signatures and provide more options for electronic warfare, future Su-35 variants are expected to follow suite. Although the USSR was 20 years ahead of the world in fielding electronically scanned array radars for air to air combat, the Su-57 is Russia’s only fighter in production with a nose mounted AESA radar. The integration of an AESA radar based on that of the Su-57 to replace the Irbis-E on the Su-35SM remains a significant possibility.
Electronic Warfare Suite
Although the Su-57’s airframe design provides wide ranging performance advantages over the Su-35, one of the key means by which the Su-35SM is expected to largely bridge the performance gap is through integration of avionics derived from those of its next generation successor. The Su-35S currently uses the KNIRTI L175M Khibiny-M electronic warfare system which provides a radio-electronic ‘protective hood’ for the fighter against missile attacks – a digital cloud that makes the aircraft far more difficult for radars to detect. The system is capable of protecting not only the fighter, but also accompanying escorts and attack groups, and is thought to have been a contributor to the fighter’s extremely low attrition rates in the Russian-Ukrainian War. The Su-35SM could benefit from a derivative of the Su-57’s ‘Himalayas’ electronic warfare system, which was first integrated onto Su-57 prototypes for testing in 2014. The system is not stored in a single area on the Su-57’s fuselage, but instead distributed across its airframe including on the wings to better interfere with enemy targeting systems and provide protection from attacks from all angles. It reportedly has a very long reach exceeding the effective use radius of Western air to air missiles such as the AIM-120D, which allows Su-57s to more effectively neutralise attacks non kinetically. Should the Su-35SM be able to accommodate a similar system, it will contribute greatly to its survivability. An advanced electronic warfare capability is particularly key due to the aircraft’s non-stealthy fourth generation airframe design, which will need to rely more heavily on such means to remain survivable on future battlefields.
As network centric warfare capabilities and sensor fusion have become increasingly central to war fighting in the 21st century, the Su-35SM is expected to seek to at least partly bridge the gap with competitors such as the American F-35 and Chinese J-20 in this area of avionics. In September 2019 details were released of the Su-57’s new combined system of communications, data exchange, navigation and identification (OSNOD) system, which allowed the fighter to function as part of a larger combat network. The system provided enhanced encryption protection and anti jamming features, and was described by the head of the Polet science and technical centre of the Russian Electronics holding Alexei Ratner as one that “ensures constant cryptographic protection of communications… In other words, intercepting them will produce no result.” Two years later at the MAKS 2021 international aerospace show the S-111 communications system was presented by Russia’s state tech company the Ruselectronics Group. “The equipment provides radio-telephone communications and an exchange of the plane’s data with other aircraft of various designation as well as with ground, aerial and naval command and control posts. The equipment incorporates the state-of-the-art technology of high-speed data transmission and features advanced network solutions,” the company stated regarding the new feature which would significantly enhance the Su-57’s network centric warfare capabilities. These technologies are all likely to be considered for integration onto future variants of the Su-35.
Although the Su-35 was designed to be a multirole fighter capable of operating in strike, anti shipping, bombing and even close air support roles, air superiority was always the program’s primary focus where the Su-57 and the older Su-30SM were more well balanced to be equally capable in all kinds of operations. The Su-57 introduced a range of new guided air to ground weapons which could be integrated onto future Su-35 variants, notable examples being the PBK-500U Drel glide bomb with cluster submunitions and an effective ‘fire and forget’ capability, and the Kh-59MK2 cruise missile. The missile has been combat tested in Syria and Ukraine – the only cruise missile used in combat by a stealth fighter – and was designed as a primary air to ground armament for the Su-57 that could fit in its internal weapons bays. It is optimised for neutralising small hardened targets at extreme ranges of over 300 km. The Kh-59MK2 could significantly improve the Su-35’s strike capabilities, although it may be cut from a planned upgrade package to reduce costs due to the aircraft’s strong focus on air superiority.
Complementing expected improvements to the Su-35SM’s electronic warfare systems, the fighter could potentially integrate a derivative of the Su-57’s Directional Infrared Countermeasures System (DIRCM). Where electronic warfare can neutralise radar guided missile attacks, this system uses laser beams to blind incoming infrared guided missiles after they are discovered by the fighter’s missile launch detector apertures. This is particularly useful in visual range air to air combat, and when operating at lower altitudes against ground based air defence systems including widely used handheld systems such as the Soviet Igla and the American Stinger. DIRCM turrets are a unique feature of the Su-57, and are mounted both dorsally behind the fighter’s cockpit and ventrally beneath it.