PLANES of FAME - SUKHOI Su-57 FELON

Update: 2022/05/28  by Robert Kysela / CHK6

The development of defence technology was and is always characterised by the approach of being ahead of the enemy by the famous nose length. In the case of combat aircraft, the premise was for a long time to fly faster and higher than the enemy machines, or to have more powerful armament. In the first two (major) wars, in which aircraft played an increasingly important role, it was these capabilities and, of course, the skill of the pilots that determined who emerged victorious from an air battle. However, the superior technology was useless if the pilot detected the enemy aircraft too late. The invention of radar allowed pilots to locate enemy aircraft long before they were visible to the human eye. This was already evident in the Battle of Britain, when the British radar stations on the Channel coast located the German bomber formations shortly after their take-off. When they then approached their target, the Spitfires and Hurricanes of the Royal Air Force were already waiting for them.

This gave the West a great technological advantage, which ironically was based on the mathematical principles and calculations published by the Russian physicist Pyotr Ufimzev in the late 1960s.

R. Kysela
Sukhoi Su-57 Prototype T-50-2 - © by Robert Kysela
Sukhoi Su-57 Prototype T-50-4 - © by Robert Kysela

Since then, the greatest danger to a fighter plane has come from enemy radar. To avoid this, all kinds of tactics were used, from adapted low-level flight (under the radar using Terrain Following Radar) to jamming measures in electronic form (ECM) to operations at very high altitudes, everything was tried out. On 17 January 1991, the USAF demonstrated to an astonished world public the use of aircraft equipped with so-called stealth technology. The Lockheed F-117A Nighthawk was the first aircraft designed with the aim of not being detected by enemy radar, or only with difficulty. This gave the West a great technological advantage, which ironically was based on the mathematical principles and calculations published by the Russian physicist Pyotr Ufimzev in the late 1960s.

Sukhoi Su-57 Prototype T-50-1 - © by Robert Kysela
Sukhoi Su-57 Prototype T-50-2 - © by Robert Kysela
While the American designers since then have relied heavily on the stealth factor in new developments, the Russians have concentrated on superior manoeuvrability. The first aircraft from Russia that has stealth characteristics and can thus be assigned to the 5th generation is the Sukhoi Su-57 (NATO code: FELON). This aircraft is the result of more than 30 years of development, which was initiated in Soviet times but realised with considerable delays due to the collapse of the Soviet Union and the subsequent economic upheaval. Due to the long development time, the first two prototypes, which were developed by the design offices of Mikoyan & Gurevich and its long-time competitor Sukhoi, no longer met the requirements of the Russian military. The MiG-designed Izdeliye (Article) 1.44 resembled the Eurofighter EF-2000 in appearance, while the Sukhoi S-37 Berkut took a completely different approach (it had negatively swept wings), but both aircraft still had a relatively large radar signature (RCS = Radar Cross Section). Therefore, in mid-2001, the Russian Ministry of Defence issued a revised specification calling for a fighter with a small radar cross section, superior manoeuvrability as well as supercruise capability. Work on the new aircraft began in April 2002 under the leadership of Sukhoi’s chief designer Alexander Davidenko, and just a year and a half later the preliminary design was presented.

The first flight of the prototype took place on 29 January 2010 (T-50-1 / Bort 051) with Sergei Bogdan at the controls.

R. Kysela
Sukhoi Su-57 Prototype T-50-1/4 - © by Robert Kysela
Sukhoi Su-57 Prototype T-50-1 - © by Robert Kysela
This aircraft was henceforth designated the PAK-FA T-50 (Perspektivniy Aviacionniy Complex Frontovoi Aviacii – Future Multi-Purpose Combat Aircraft of the Frontline Air Forces). The first flight of the prototype took place on 29 January 2010 (T-50-1 / Bort 051) with Sergei Bogdan at the controls. To date, 9 prototypes have been built, with one machine being used exclusively for ground tests. In the meantime, series production has already started. By the end of 2021, however, just three series-produced machines had been delivered, with four more machines in the pipeline this year. As of today, the Russian armed forces have an order for 76 aircraft. Originally, India was intended to be an equal partner, but the Indians dropped out of the project in 2018. Delays, but above all the fact that the Indians were not given the feeling of being a full partner, contributed significantly to the decision. The lack of communication on the part of the Russians and their proverbial secrecy were probably the icing on the cake!
Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela
Sukhoi Su-57 Prototype T-50-4 - © by Robert Kysela

As a basis for the Su-57 layout, the Sukhoi designers used a so-called blended wing body (the fuselage merges seamlessly into the wings and is part of the aircraft’s lift) with delta-shaped wings and a V-shaped double tailplane. This configuration keeps the construction very flat. The wings have a sweep angle of 48° in the front section, the rear section has an angle of 14°. The same applies to the tailplane which, like the double rudder, is designed as a pendulum rudder (the entire tailplane is movable). The air intakes are designed to provide sufficient airflow to the engines in any attitude and even at extreme angles of attack. Instead of canards, the Su-57 uses so-called LEVCON’s (Leading-edge Vortex Controllers). These are movable slats which, together with the variable, three-dimensional thrust/vector control, give the Su-57 enormous agility, also known as supermaneuverability.

Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela
Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela

Stealth characteristics in aircraft are not solely determined by the shape of the aircraft. In fact, the influence of the shape accounts for about two thirds, the other third is generated by the use of radar-absorbing materials such as composites as well as a special coating. Also important is a very clean and smooth finish of the surfaces. Unclean joints (butt edges), the smallest distortions as well as countersunk screws/rivets that are not absolutely flush and cleanly filled with the planking have a negative effect on the RCS. In the Su-57, almost 70% of the surface materials consist of composite materials. The interior of the wing and control surfaces is made of an aluminium honeycomb structure, which not only ensures high stability, but also has an absorbing (scattering) effect on radar beams.

The Izdeliye 30 is equipped with a fully digital engine control system (FADEC), which ensures that the engine operates at the highest possible efficiency under all conditions.

R. Kysela
Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela
Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela

Two brand-new engines from the manufacturer UEC NPO Saturn are planned for propulsion, which currently still bear the internal designation Izdeliye (Article) 30. This is a two-shaft turbofan engine with a low bypass ratio. The turbine’s guide vanes (in the inlet section) are made of composite materials, and the three-dimensional thrust nozzle is of convergent-divergent design. The rear shape of the thrust nozzle is serrated to make detection by radar difficult here as well. The Izdeliye 30 is equipped with a fully digital engine control system (FADEC), which ensures that the engine operates at the highest possible efficiency under all conditions. Performance figures are quoted by the manufacturer as 108 kN dry thrust and 176 kN thrust in afterburner mode – about 25% more than the AL-41F1A currently in use. This will give the Su-57 a very high super cruising speed (estimated at over 1800 km/h), and the top speed is even said to be over 2600 km/h. The range (with internal fuel load) is said to be more than 3000 km, and the Su-57, like most modern fighter aircraft, has the capability of air-to-air refuelling.All prototypes as well as the first production aircraft are still powered by the NPO Saturn 117S (AL-41F1A), as testing as well as production of the Izdelije 30 has been slow. The first machine in which a pre-production model of the Izdeliye 30 was installed was the 2nd prototype (T-50-2 / Bort 052). However, only an Izdeliye 30 was installed on the left side, with an AL-41F1A still acting as the right engine. The first test flight in this configuration took place on 05 December 2017 (again with Sergei Bogdan at the controls). Delivery of the first Su-57 with the Izdeliye 30 is not expected before 2024. All (series) aircraft delivered by then are to be converted to the new engine.

To date, the design of stealth fighters has been primarily tuned to the X-band range (8 GHz to 12 GHz).

R. Kysela
Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela
Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela

The Su-57’s on-board radar does not consist of a single radar antenna housed in the nose segment of the aircraft, but of several units that communicate with each other. In addition to the main antenna (Tikhomirov NIIP N-036 / X-band range), which is traditionally located in the nose, there are two other AESA elements (N-036B / X-band range) on the side of the forward fuselage segment and two N-036L modules in the wing leading edges. Most interesting are the last two AESA radars. These operate in the so-called L-band range (1 Ghz to 2GHz of the radio spectrum). To date, the design of stealth fighters has been primarily tuned to the X-band range (8 GHz to 12 GHz). Therefore, an L-band radar can locate an enemy stealth aircraft earlier than is possible with an X-band radar, no matter how powerful. The L-band radar can also be used in passive mode, where it can detect electronic emissions from enemy aircraft at long ranges and even jam them sensitively (e.g. communication systems such as the MIDS/Link-16 or even the enemy’s friend-or-foe detection system IFF, which also operates in the lower GHz range). As with the Russian 4th generation fighters (Su-27/30/35 series; Mig-35), the Su-57 also has a very efficient passive infrared locator system (OLS – Optical Locator System) called 101KS Atoll. This is capable of detecting the heat signature of an enemy aircraft (or a fired guided missile) at a range of up to 70km.

Sukhoi Su-57 Bort054 - © by Robert Kysela
Sukhoi Su-57 Bort051/2 (1st & 2nd Prototype) - © by Robert Kysela

Another important factor is the implementation of AI (artificial intelligence) in the avionics of the Su-57. This should not only be part of the quadruple-redundant IMS (Information Management System), but also support the pilot as a kind of electronic co-pilot with the ability to think, especially in a possible attack scenario, or take over the control of the defensive measures. How far Sukhoi’s software developers have come in this area is still completely in the dark. The use of AI runs parallel to the development of the so-called Loyal Wingmen concept. Here, a Su-57 forms a team with a Sukhoi S-70 Ochotnik (Hunter) drone. According to information from the manufacturer, a two-seat version of the Su-57 is also being planned, which can operate in tandem with up to four! Okhotniks. The first flights with the S-70 were still completely controlled from the ground, the future goal is to use the UCAV’s as semi-autonomous combat units. The concept has been in flight testing since September 2019, or in the evaluation phase for a possible operational scenario.

Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela
Sukhoi Su-57 Bort051 (refurbished 1st Prototype) - © by Robert Kysela

In terms of armament, Sukhoi’s designers were able to access a wide range of guided weapons and bombs. Especially the latest variant of the KTRV R-77M (NATO code: AA-12 Archer) is causing the West some headaches. This medium-range missile has an enormously powerful APAA seeker (Active Phased Array Antenna), as well as a dual-pulse engine, and a laser proximity fuse. The latter makes the R-77M particularly insensitive to electronic jamming. For close air combat, the Su-57 is equipped with a 30mm rapid-fire cannon (1800 rounds/min) of the type 9A1-4071K. The Su-57 has 2 spacious internal weapon bays in the centre fuselage area, two further internal weapon bays in the inner wing area, as well as six possible external underwing stations.

Sukhoi Su-57 Bort511 (10th Prototype) - © by Robert Kysela
Sukhoi Su-57 Bort053 (3rd Prototype) - © by Robert Kysela
The Su-57 is not uncompromisingly trimmed for stealth. This may prove to be a groundbreaking concept in the near future, as the introduction of increasingly powerful tracking systems, such as so-called passive radar, may quickly render obsolete aircraft whose only advantage is their stealth property. Whether the Su-57 is equal to or even superior to other 5th generation fighter aircraft, such as the F-22 or the F-35, cannot be said with certainty at the moment. While the Russian side emphasises the superiority of its product in every statement, the Western side is engaged in a propaganda war that puts the Su-57 in a bad light in every way. However, numerous features of the Su-57 can certainly act as game-changers and thus create the famous nose-length advantage that was mentioned at the very beginning of this article!
 

Robert Kysela  / CHK6

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