Realty Of Russian Aerospace Industries: China upgrades Russian-made Su-35 for PLAAF

China placed an order of two dozens Su-35 ‘4++ generation’ fighter in November 2015 alongside two regiments of the S-400 long-range surface to air missile system.

The People’s Liberation Army began to receive the fighters little over a year later in January 2017, with the delivery completed by mid-2019 with two dozen aircraft entering service – enough to form a single squadron.

China has previously been a leading client for Russian fighters, ordering over 100 Su-27 jets and almost 100 of the newer Su-30 platforms in the 1990s and the early 2000s. The much smaller contract for Su-35s was a result of significant advances in Chinese military aviation which had reduced its reliance on foreign designs, with the J-11B entering service in the mid-late 2000s based on the Su-27 but fielding far more capabilities, and the J-16 joining the fleet in 2013 as China’s first indigenous ‘4+ generation’ aircraft.

Why Did China Buy Su-35?

The engines in the J-20 are the Saturn AL-31, which the Russian used in Su-27 decades ago. Even after making significant progress in the aviation industry, China still could not produce modern engines that could complement the J-20. There is only one way to get a new powerful engine in a short time is to buy jets having it and then reverse engineer the engines. One of the many things, Chinese are good at is Reverse Engineering.

Saturn AL-31 117S Engines

The Chinese bought the Su-35 only for their Saturn AL-31 117S engines. They already have planes comparable to Su-35, like J-11 (copy of Su-27), and J-31. Thus it is clear that the 24 Su-35 were mainly bought for their engines.

China is new to this arena and is mostly just gaining experience. The Chinese can’t produce a jet engine that is suitable for what fighters require

China’s interest in the Su-35 is widely thought to have been influenced by the need for a technology transfer from Russia – primarily technologies pertaining to three-dimensional thrust-vectoring engines – rather than because of a need for the aircraft themselves.

While the Su-35 (Su-27M) is a fighter based on Soviet-era Su-27 airframe, as of 2020 it’s capabilities notably lag behind those of indigenous Chinese J-11A aircraft in many key fields.

Over the coming decade, the aircraft will increasingly be considered at the lower end of the Chinese fleet, particularly in terms of its sensors and armaments, which provides the PLA with a strong incentive to upgrade the aircraft domestically.

A look at four major upgrades China made in Su-35

PL-15 Active-Radar Homing Missile

PL-15 active-radar guided air-to-air Missiles

One of the most outstanding weaknesses of the Su-35 relative to new Chinese AESA radar-equipped fighters such as the J-10C, J-11BG, J-16 and J-20 is the limited capabilities of its air to air missiles.

The R-77 was the first semi-active radar-guided missile developed for Russian fighter-sized aircraft, and while it lacks behind the American AIM-120C and Chinese PL-12D/PL-15 with a heavier warhead and longer range its performance is very limited compared to newer U.S. and Chinese designs.

While the American AIM-120D introduced in 2014 was intended to provide an advantage over rival designs for at least a decade and had a formidable 160-180km range, the Chinese PL-15 achieved similar range like the AIM-120C/D.

The new Chinese missile not only has a much longer range close to 200km, as well as a heavier warhead but is also guided by an active-radar rather than a passive radar. This makes the missile much more difficult to jam, allows it to better lock onto the fourth generation and fourth++ aircraft at longer ranges and overall provides superior reliability to the Russian designs.

The significant capability gap between the Su-35’s air-to-air missiles and the PL-15 is thought to be the primary cause behind the Russian fighter’s poor performance in combat simulations, actual combat in Kashmir conflict in India and equipping it with theses or similar missiles is vital to prevent it falling behind as a growing proportion of China’s fighter fleet is equipped with the new missiles.

R-37M/ PL-21

R-37M Long-Range Air-to-Air Missile

A second option for upgrading the Su-35’s long-range arsenal could be to equip it with missiles specialized in targeting enemy support aircraft such as tankers and AWACS. One option could be to equip the fighters with the Russian R-37M missiles, which with a 400km range and Mach 6 speed were designed to threaten both fighters and support aircraft but are particularly dangerous against the latter.

Another would be to equip them with PL-21 missiles, which are currently being developed for the J-16 fighter and have an estimated range of over 400km. The PL-21 has a number of advantages over the R-37M, which aside from its longer-range include active-radar guidance includes a secondary seeker which uses infrared guidance for improved reliability.

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While it is more likely given its strengths in close-range engagements that China will equip the Su-35 with PL-15 missiles rather than relying on it to hunt support aircraft over extreme distances as the Russian onboard radar is not capable of detecting fighter aircraft with less 1sqm RCS, the possibility remains that the Su-35 fighter could be relegated to such a role. 

Su-35 ‘4++ Generation’ Fighter

AESA Radar

One of the Su-35’s primary shortcomings compared to its Chinese counterparts is its lack of an AESA radar, with a passive radar not only providing lower efficiency but also being much easier to jam.

While the Russian Air Force is notably considering integrating an AESA radar being under development for the Su-57 and MiG-35, China’s greater familiarity with such technologies could allow it to do this domestically at a much lower cost.

KLJ-7A

The PLA began to integrate AESA radar onto its fighters from 2013 with the J-16. Chinese AESA radar technologies are thought to be considerably ahead of those of Russia, and a new generation of these radars is behind scheduled delivery.

These could replace the Su-35’s Irbis-E phased array radar, which lacks situational awareness and a less reliable sensor suite. 

PL-10 Short range air-to-air missile

PL-10 Short Range Air to Air Missile

Another shortcoming of the Su-35 is its reliance on the R-73 air to air missile for short-range engagements. The design was considered the most capable of the Soviet-era and has been modernized considerably since, but ultimately is far inferior to its newer Chinese counterpart the PL-10E.

The new Chinese missile is fitted with a multi-element infrared seeker capable of engaging targets at +/-90 degree off-boresight angles. It is paired with the helmet-mounted displays used by modern Chinese aircraft to allow pilots to track targets beyond the aircraft’s radar scan envelope using the high off-boresight capability, with the pilot able to lock on by simply turning his head towards the enemy aircraft.

This provides Chinese jets with a considerable advantage over their competitors at close ranges, complementing the manoeuvrability advantage provided by three-dimensional thrust-vectoring engines.

The missile would complement the capabilities of the Su-35’s airframe at close ranges provided by its high thrust/weight ratio and three dimensional thrust vectoring engines.

Radar Absorbent Material (RAM) Coatings 

J-16 Fighter with RAM Coatings

China is working towards stealth technologies with a particular emphasis on radar-absorbent paints, and alongside applications on its J-20 fighter, it has also applied them to fourth-generation aircraft with RAM coatings – namely the J-10C and J-16.

These coatings at present are thought to give all of these new Chinese fighters a reduced radar cross-section relative to the Su-35, and application of similar coatings to the Russian built jets would make them considerably more survivable at long ranges.

Given the considerable investment in the field, Chinese RAM coatings are likely to far supersede their Russian counterparts including any coatings which may be applied to the upcoming Su-57 next-generation fighter and will ensure that the Su-35 does not have a major disadvantage in terms of capabilities relative to other Chinese jets. 

Chinese PLA Su-35 ‘4++ Generation’ Fighter without RAM Coatings

Ultimately, with China’s defense sector surpassing that of Russia in a growing number of fields, air to air missiles being a particularly notable one, it can be expected that China will attempt to integrate at least some upgrades onto the Su-35.

The result could very well be the most capable Russian built fighter ever for air to air combat – potentially surpassing the capabilities of the newer Su-57 which at least for the foreseeable future will not have access to comparable missile classes or RAM coating technologies, and which may be forced to rely on an inferior AESA radar to that provided by China’s own defense sector.

Whether China will purchase further Russian fighters, with the Su-57 having a number of strong selling points including its use of hypersonic missiles, — the only motivation for China to buy Su-35 is to gain access to a new engine and prospect of reverse-engineering the engine and produced the same engine domestically. 

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