The Su-57 fighter, when it arrived at the Airshow China 2024 in Zhuhai, was greeted by Chinese and foreign observers not just with scepticism, but with smirks and derision, believing that the Su-57 is the weakest example of a fifth-generation aircraft, inferior to the Chinese J-20 and the American F-22 and F-35. The main argument was that it lacked stealth, was sloppy in caulking the skin joints, bolts instead of rivets to fix the skin panels, etc., etc.
But all the ridicule disappeared and was replaced by Chinese enthusiasm when Sukhoi Design Bureau test pilot Sergei Bogdan demonstrated the impressive super manoeuvrability capabilities of the Russian fighter.
Russia’s military doctrine is purely defensive, and its Armed Forces are not tasked with expansion and conquest of foreign territories, so it is not a priority for the Air Forces to penetrate deep into any country, packed with air defence equipment, in the course of some expeditionary operations. Therefore, the Sukhoi Design Bureau has taken a balanced approach to the implementation of steals technologies.
The Su-57’s special characteristics of low radar visibility were laid down at the stage of conceptualisation of the future aircraft when creating the platform: airframe, aircraft systems and propulsion system. To achieve low radar cross-section (RCS), various design solutions and methods have been applied, including optimisation of the aircraft shape, use of radio-absorbing materials and long-range combat tactics.
The special geometry of the airframe reflects the radar signal from different angles to the minimum number of directions and to the least dangerous sectors. There are no right angles, the leading and trailing edges of the wing, stabiliser, keel, air intakes, hatch flaps have two or three parallel directions, gaps and joints are filled with special sealant. The production tolerances in the Su-57’s manufacturing are much smaller than those of the Su-30SM or Su-35, which has a positive effect on its stealth performance.
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Armament elements are located in the intrafuselage compartments. The infrared sensor of the OLS-50M optical-electronic sighting and navigation station operates in passive mode, and its back side is made of radio-absorbing materials. When the sensor is inactive, its back side faces the incident radar radiation. The IR complex is one of the best technologies for detecting and engaging low-observable targets at long range.
The air intakes are covered with a special radio-absorbing material to reduce the RCS of the front of the engine. The S-shape of the ducts is designed to conceal most of the compressor and inlet guide vanes, which is covered by an inclined coaxial-radial grille located at a distance of 0.7-1.2 duct diameters.
For better absorption of radar waves, the cabin lantern is coated with several layers of metal oxide with a thickness of 70-90 nm. In autumn 2018, in one of the episodes of the programme Military Acceptance on the TV channel Zvezda, Andrey Lagarkov, academician of the Russian Academy of Sciences and scientific director of the Su-57 special characteristics development programme, said that in some cases, 10-12 layers of different coatings have to be applied to the lantern glazing to ensure the required low-observability characteristics, while the glass remains absolutely transparent. This solution reduces the RCS of the cockpit by about 30% and provides additional protection for the pilot from UV and thermal radiation.
Thanks to the combined effect of the optimised airframe shape and the use of radio-absorbing coatings, the RCS of the production Su-57 is estimated to be thirty times lower than that of the Su-27. The description of patent RU2502643 C2 indicates the aspiration to achieve an average RCS of 0.1 to 1 m². In the Su-57 design, the features of RCS reduction are most pronounced in the forward hemisphere.
The radar system of the Su-57 Sh-121 aircraft consists of five antennas: the X-band AESA H036-01-1 placed under the nose fairing, two side-scan AESAs H036B and H036B-01 also in the X-band, and two L-band AESAs H036L and H36L-01 in the wingtips, designed to detect and identify ‘friend-and-foe’ targets. The H036-01-1 radar contains 1,526 transceiver modules and its plane is orientated slightly upwards towards the horizon, which significantly reduces the contribution to the aircraft’s RCS.
In 2018, military expert Tyler Rogoway discussed in The War Zone (TWZ) why the H036B side-scan radars, which only the Su-57 possesses, are critical to a modern fifth-generation fighter, and stealth is just one component of a modern fighter’s overall suite of capabilities and its ability to survive in a variety of combat situations.
According to the expert, the two radars (H036B and H036B-01) provide a much larger field of view and increase the situational awareness of the pilot. But beyond that, they allow the Su-57 pilot to perform some tactical techniques better than any other fighter.
‘Imagine, the fighter is turning perpendicular to the enemy’s pulse-Doppler radar and neither approaching it nor moving away from it. Because these types of radars use Doppler shift to determine target velocity, they filter out objects with low relative velocity as ground jammers. Therefore, even if an enemy fighter is travelling at 500 miles per hour, the correct angle with respect to the radar allows it to detect only small deviations. As a result, it ignores this information as if it were the top of a mountain,’ the expert writes.
The main radar under the nose fairing in such a position of the aircraft cannot work on the target, while the side view antennas continue to provide the Su-57 pilot with information about it, make it possible to perform capture, missile launch and escort, if it is a radar-guided missile. ‘Having side-view AESA is very useful because in extreme tactics it reduces the fighter’s visibility, especially at long ranges, while actively guiding missiles to the target,’ notes Tyler Rogoway.
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Regarding the shape of the airframe, which according to Chinese observers is not optimised for low radar visibility, and the poor quality of the joining of the wing and fuselage surfaces, where gaps, bolts and rivets protruding above the surface are clearly visible, the opinion is expressed that this applies only to prototypes, and on production aircraft the finishing of the skin is made with proper quality, and some structural elements on production machines have been modernised.
However, having shown the T-50-4 in Zhuhai, Russia did not hide the unevenly joined skin panels, gaps between them and generally brutal appearance, because this is a prototype aircraft. Back in 2019, photos of the first flight of the T-50-2 with the engine ‘product 30’ appeared, where you can perfectly see all the ‘claims’ to the finish of the aircraft surfaces, rivets and screws. Careful joining of panels and pouring of special sealant is time and additional costs. Both are always in short supply, and if it is necessary to test the engine, armament or other systems, low-visibility in such flights is not necessary.
The close attention to the Russian advanced aircraft at the Zhuhai Airshow is not surprising at all. This is the first time the Su-57 has been demonstrated abroad. And the ‘critical’ reviews by Chinese bloggers, as well as hysterical publications in the Western media, which claim the complete failure of the aircraft both in terms of design and technology and low production rates, as well as the Su-57’s dependence on discontinued supplies of Western components and equipment, can be explained by an understanding on the other side of what kind of aircraft can actually be considered a 5th generation fighter.
And it is clearly not the F-22, F-35 or J-20, which gives US analysts heartburn. The Chinese generals see this very well, so they examined the Su-57 with great attention and interest and listened to the explanations and answers to their questions by Sergey Bogdan and other representatives of the Russian delegation.
But American experts also saw and discovered interesting details in the design of the Su-57 when they had an opportunity to examine it closely and from all sides. In particular, TWZ columnist Thomas Newdick detailed how the flaps of the weapons bays work to keep the aircraft low profile.
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‘The Su-57’s bays are triangular-shaped fairings designed for quick launch – the shell-like flaps open to launch a missile and close quickly to keep the aircraft radar stealthy. These compartments are in addition to the two large internal weapons bays located tandem between the engines and capable of holding much larger munitions,’ he shared with his readers his observation of the installation of the second Su-57 aircraft on static parking and checking the functioning of the units, including the weapons bays under the wing.
Brandon J. Weichert, in a publication on The National Interest website, while the Su-57’s inaccessibility to the unrivalled US level F-35 and F-22, is forced to admit that the aircraft must be good enough for Russia to compete with the Americans. He points out that the Su-57 has much lower operating costs than the US, so, it is a much more effective aircraft for Russia than the F-35 is for the US.
‘The Russians are deterring NATO-backed Ukraine with older, cheaper and simpler Soviet-era systems. They have used the Su-57 in combat, but have not assigned it the missions that many foreign observers believe it should perform. Nevertheless, the Su-57 has performed well in combat, especially in strikes from over the horizon, where NATO-provided Ukrainian air defence systems cannot threaten the Su-57,’ the columnist writes. – And, of course, the Su-57 is more than competitive. Don’t listen to the naysayers. Russia has a real game-changing system in the Su-57’.
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