Underrated stealth capability of Su-57

Underrated stealth capability of Su-57

-Palash Choudhari

Since the first flight of its prototype, media websites and news networks have been engaged in a constant smear campaign to somehow tarnish the image of Brand Sukhoi. They resort to spreading false unverified claims about Su-57 in an attempt to build a false narrative against it. The critics simply make statements that aren’t backed by any credible proof and no understood reason. People who have already formed their mind about Russian technology being in bad light pick these statements and amplify the unverified claims confirming the narrative. This is everywhere now and wherever you speak about Su-57, people would jump in with statements about how the radar cross section of Su-57 makes it unworthy to be even called as a 5th generation fighter. This article aims at explaining the measures taken to make Su-57 a very low observable aircraft.

Frontal shaping of Su-57

Undoubtedly, the frontal portion of Su-57 has been optimized for reduced radar wave reflection at specific angles. The leading and trailing edges of the wings, control surfaces and the serrated edges of skin panels are carefully aligned at specific angles in different locations to reduce the number of directions the radar waves can be reflected. The periphery around air intakes has a complex shape of flat surfaces blended together in a fashion that enables deflection of radar waves in a direction away from the radar. The cockpit and fuselage have similar faceted VLO shaping. The Su-57’s antennas are recessed from the surface of the skin to preserve flatness of the surface.

Fully articulated, reduced aspect ratio dorsal fins that are canted outwards, blended movable LERXs (Leading Edge Root Extensions) and clipped trapezoidal wings similar to F-22 add to the shape enabling a VLO design. The top view of Su-57 resembles a “flattened flanker” with spaced engines, tails and large fuselage. The wing body blended design is more evident from the top view as is the blending of cockpit in its mid-section. It resembles a pyramidal shape with flat surfaces intended to deflect radar waves. Similar to what’s seen on the YF-23, in Su-57 cool air that flows in between the engines and around the engines mix with the exhaust hot air thereby reducing its overall temperature. This contributes to a reduction in thermal signature.

Aft shaping of Su-57

The initial prototype didn’t show much focus on the shaping at aft body and was quickly taken by observers as negligence, lack of funding or inexperience in designing a stealth aircraft. But the later variants and production aircraft showed unanticipated improvements that show a proper focus on RCS reduction in the aft fuselage.

To begin with, all the moving stabilizers are very well shaped for radar wave deflection. The surface at the aft fuselage (just aft of the bays where rear landing gear retracts) matches the flatness at other areas on the blending of wing-body. The engines are covered with the same radar absorbing carbon fiber composite structure as any other surface of the aircraft. The tail boom that houses an antenna of L-402 Himalayas electronic warfare system has also been shaped as blend of multiple flat surfaces to deflect radar waves.The Izdeliye-30 engine that Su-57 is ultimately going to have has low observable axisymmetric nozzles completely similar to F-35.

Radar Blockers

To mask the significant RCS contribution of the engine face, the partial serpentine inlet obscures most, but not all, of the engine’s fan and inlet guide-vanes (IGV). In the intake passage there is a set special device, partially overlapping in the axial direction of the GMV preventing electromagnetic waves. In addition to screening, this constructive solution separates inlet channel into several different cylindrical or planar voids, and, flat surface of the cavities can be both parallel and intersecting. Such a complex segmentation and channeled air intake cover wall segments with radar absorbing materials reduces the power of the electromagnetic waves reflected from the engine face and from wall cavities, thus providing a decrease of the RCS in the forward hemisphere of the aircraft. The radar blockers provide a further reduction in RCS of the frontal hemisphere.

Radar Absorbent Materials

The aircraft uses RAM to absorb radar emissions and reduce their reflection back to the source, and the canopy is treated with a coating to minimize the radar return of the cockpit and pilot. The optical windows of IRST and DIRCM are made of luco sapphire which is one of the strongest transparent material, also provides excellent RCS reduction. The IRST is turned backwards when not in use and its rear is treated with radar absorbent material to prevent radar signal returns.

RCS

The RCS of Su-57 as quoted by its chief designer is around 0.01 m². This figure was quickly taken by western bloggers and was used to dub Su-57 less stealthy. But in reality the method of assessing RCS is different in Russia. The manner in which average value of overall RCS is taken is different. The chief designer of Su-57 also said that the overall RCS of F-35 would be around 0.3 to 0.4 m² (according to Russian methods of average RCS assessment). Above given is a graph of radar engagement range versus target RCS of F-22’s AN/APG 77. The detection range for 0.01m² target is below 40 kms. Somewhere between 35 to 40 km, there are no other means of targeting F-22. The F -has to wait until Su-57 comes as close as 40 kms. All this if Su-57’s current RCS figures are judged true.

Why India pulled out of Su-57 project?

India has to pay huge amounts of “royalties” to the Russians whenever they have to make a hardware or software change in Su-30MKI aircraft. The SU-30MKI constantly keeps upgrading in hardware and software. Weapons integration like Brahmos ALCM or the structural changes made to accommodate the heavy launcher for Brahmos missile, all cost a lot. While developing the Su-30 MKI Indian airforce pilots and HAL engineers were actively involved in its development and made contributions in the canard design and enlargement of LERXs but no credit was given to Indian engineers. Even during the development of MiG-29K Indian engineers used their own technical expertise to increase internal fuel volume and elevators of the type. India also contributed in money just to keep the Mikoyan Design Bureau afloat with exactly no credit in return.

The Su-57 will have a totally different role in IAF and hence a separate variant named FGFA was proposed even though it was originally proposed that Indian and Russian side would have 50% contribution in intellectual property rights, research and costs, the Russians denied to give design ownership to Indians. To add to all the issue the Izdeliye-30 engine wasn’t supposed to be ready until 2024. The Indians realized that the Russian prospect of becoming a defence manufacturing power without having the financial and human resource ability is totally impractical. So Indians decided to exit the program to save costs and commented that they may join at a later stage when the project is mature enough to be called as a product.

Unlike the false news reported everywhere Indians were never dissatisfied with the design and concept. Indians invested money and contributed scientists and engineers during the development preliminary studies and concept development stage.

Su-57 v/s other 5th generation fighters

I have zero knowledge about the level of advancement of Chinese so I won’t comment on J-20. But Su-57 is obviously less stealthy than F-22 and F-35. The Americans have decades of experience in development of stealth fighters. This nowhere means that the Su-57 is anywhere less stealthy than any other fighter aircraft in 4+ generation. The Su-57 is more stealthy than any 4+ generation fighter aircraft including the Rafale that has spectra EW suite. The Su-57 is stealthy enough to deny long range detection by ground and AWACS based radars to the point that it can penetrate into enemy airspace. Its visit to Syrian battlefield completely undetected is a testimony that Russians have done a good job in their first attempt.

Interested to know about the status of AMCA? Read here.

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