The configuration of the Sukhoi Su-57 Felon is an evolution of the Su-27’s shape adapted for the requirements of low visibility and supersonic speed and agility.
According to Sukhoi, the Su-57’s radar cross section (RCS) is reduced to an average figure of 0.3-0.4m2 compared to 15m2 for the Su-27. As explained by Piotr Butowski in his book Russia’s Warplanes, Volume 1, the main solution to reduce radar visibility is internal carriage of weapons. Radar blockers reduce reflections from the engine inlet guide vanes and are installed in the engine air intake ducts. The shape of the airframe has been selected to reduce the number of directions in which electro-magnetic waves are reflected, and to ensure these directions are the safest.
Another group of stealth measures concern the fighter’s equipment. The surfaces of the NO36 radar arrays are deflected from the vertical plane, thus deflecting the enemy radar’s radiation aside. The domes of the arrays are selective — they let their own signal pass through and block other frequencies. In addition, the compartments for these arrays feature radar-absorbent coatings on their edges to absorb ‘freak waves’ (which occur when a wave is amplified after multiple reflections within an enclosed space). In order to reduce their total number, the available arrays are used by multiple systems simultaneously, for example, the radar, ECM and IFF systems. Within the antenna-feeder system, use is made of antennas that do not protrude outside the airframe outlines, and the vertical empennage serves as an antenna for the communications suite. The turret of the 101KS-V IRST is rotated backwards in cruise configuration, and its rear hemisphere is covered with a radar-absorbing coating.
Interesting features of the Su-57 that no other fighter jet has are the longitudinally arranged internal weapons bays and the 101KS-O DIRCM (Directed Infrared Counter Measures).
‘Technically this feature is seen on other turbine powered aircraft,’ Connor Dalton, aircraft and incidents researcher, said on Quora. ‘It’s just never appeared on anything outside of heavy lift transports, and helicopters prior to the Su-57.
‘DIRCM consists of two laser emitting turrets, with one placed behind the cockpit on the dorsal side, and the other beneath the cockpit on the ventral side. The function of the system is relatively straight forwards. When an IR missile is spotted, the lasers quickly aim for the missiles seeker system, blinding it and preventing it from being able to guide to the targeted aircraft.
‘The thing is, the system has never previously been seen outside of transports and helicopters, and has only ever been placed on the ventral side in the past, as a defense against MANPADS.’
‘So, the presence of the dorsal mounting, and on a fighter no less means that not only is this the first DIRCM system ever put into a fighter, it’s one of the first DIRCM systems ever made with the goal of combating air to air missiles.’
Photo credit: Chinese Internet and Sukhoi
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