It’s not just Su-57 being less stealthy than F-35 (-40 dBsm) – it has a 1,000 times bigger RCS.
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.
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.
However, even though the Su-57 is marketed as fifth generation fighter, the Felon is not a true stealth fighter and it can’t be compared to the US-made F-22 Raptor and F-35 Lightning II. Why is that?
‘Imagine if Boeing were to market F/A-18 Super Hornets or F-15 Silent Eagles with Enclosed Weapons pod and weapon bays as a ‘Stealth aircraft’ along the lines of 5th gen. aircraft, how do you think they would compare to F-35?,’ says Abhirup Sengupta, an aviation expert, on Quora.
‘That’s analogous to calling Su-57 a direct competitor to the F-35 and F-22. Sukhoi’s own patent claims Su-57 having a design RCS between 0.1 and 1 m^2.
For a known aircraft [Su-27], the EPR value is about 10–15 m 2.
The technical result, the achievement of which the invention is directed, is to reduce the magnitude of the aircraft radar visibility to an average value of the order of 0.1 – 1 m 2.
Sukhoi Su-57 Patent – RCS Reduction
‘That’s comparable to a clean Super Hornet and it shouldn’t be a surprise when Su-57 follows many of the same RCS-reduction measures such as using radar blockers to hide the engine face instead of an actual serpentine duct.
‘It’s not just Su-57 being less stealthy than F-35 (-40 dBsm) – it has a 1,000 times bigger RCS. Since detection range is proportional to the 4th root of RCS, a 1,000 times bigger RCS equates to 5.6 times greater detection range. And this is after giving Su-57 every benefit of doubt, the F-35’s RCS is very likely closer to -50 dB.’
‘The F-35 will be enjoying almost 6 times greater detection range against Su-57. The difference is so huge that Su-57 will be hopelessly outclassed. We see this time and again in Red Flags and Northern Edge with F-35 having 28–1 kill ratio against modern 4th gen. aircraft backed by AWACS and SAMs. The enormous difference in detection range from Stealth is the primary factor for such a lopsided kill ratio.
‘It doesn’t matter how capable radar or EW suite you have, they simply can’t compensate the enormous difference in detection range from a VLO airframe. You can have amazing performance at airshows but without Stealth you’re not gonna be in a fight against 5th gen. aircraft.
‘And this is ignoring the infancy of Su-57 program and consistent delay in the production/IOC since last 4 years or the fact Su-57’s avionics suite is not remotely comparable to that of F-35. The F-35 has a bigger and much more capable radar and orders of magnitude more powerful EW suite giving vastly superior Situational Awareness.
‘Where F-35’s DAS make it the only Fighter to fully operate in the IR spectrum, Su-57 can’t even use its forward-hemisphere IRST without further ruining its RCS. The IRST is turned backwards in Su-57 because it’s a sphere, the worst shape in terms of RCS that uniformly reflects in all direction.
‘Despite all the problems with Su-57 program including lack of existence or international interest, the fundamental design is so far behind F-35 in terms of both Stealth and Situational Awareness – two key aspects of a 5th gen. aircraft. The Su-57’s design is closer to that of modern 4th gen. than it is to either F-22 or F-35.
‘Yet the Su-57 is portrayed as an equal counterpart to F-22 and F-35 with people talking about its kinematic performance or side-arrays without even understanding their actual purpose, let alone the impact on EMCON. How great are the Directed IRCMs (Laser turrets) while turning a blind eye to the fact Su-57 use a UV based Missile Warning System – making Su-57 significantly vulnerable to BVR missiles. 10 years since first flight and there’s no indication of K-77M or K-74M anywhere close to being operational, forcing Su-57 to fly with R-77 & R-74 externally (as they won’t fit inside).’
‘Imagine the kind of articles you’d see if F-35 didn’t have an operational missile that could fit internally. The Su-57 gets away with all the shortcomings using propaganda and fantasies, the likes of non-existent L band radar.
‘The Su-57 is nowhere near F-35 for similar reasons as to why F/A-18 Super Hornets are nowhere near F-35. The gap in Stealth and ultimately Situational Awareness is just overwhelming.’
Photo credit: U.S. Navy, Boeing, Sukhoi and Chinese Internet