The Indian Air Force has raised detailed technical concerns over the stealth performance of Russia’s Su-57E fighter, focusing on shortcomings that undermine its radar signature reduction, especially in the rear-aspect domain, reported Hindi vernacular website Zee News.

Sources indicate that the IAF’s evaluation team has found the aircraft’s exposed engine section to be one of its most serious vulnerabilities, negating much of the benefits achieved through frontal shaping and radar-absorbent coatings.

IAF experts noted that the open engine panels and nozzle layout resemble legacy Soviet designs, particularly that of the Su‑27 family. This configuration results in an enlarged radar cross‑section (RCS), making the aircraft detectable by hostile sensors. Preliminary assessments indicate the Su‑57E’s RCS ranges between 0.1 and 1 square metre from the frontal sector, substantially higher than the Lockheed Martin F‑35’s 0.001 square metre rating.

Aviation specialists familiar with the IAF evaluation observed that Russia prioritised engine thrust over low‑observability refinement, opting for greater power output rather than stealth perfection. The Su‑57’s Saturn AL‑41F1 engines offer exceptional thrust‑to‑weight performance but at the cost of an elevated RCS and thermal signature. This design philosophy diverges from the Western approach that integrates propulsion efficiency with stealth optimisation.

Officials conveyed these findings to Russian representatives, warning that India would not finalise procurement discussions until stealth deficiencies were addressed. The evaluation forms part of India’s multi‑billion‑dollar procurement plan for 114 next‑generation fighters, estimated at around 20 billion USD. The Su‑57E was among the prime contenders under consideration for advanced air dominance roles.

In response to Indian feedback, Russia’s defence industry has reportedly tested new composite panels and heat‑shield assemblies at the Gromov Flight Research Institute. These structural revisions are designed to conceal hot zones and reduce IR emissions by 40‑50 percent.

However, India is seeking a firm timeline for these upgrades, with clarity on whether such improvements will coincide with the full integration of the second-stage AL-51 (Izdeliye 30) engine. The IAF is reportedly unconvinced that the current AL-41F1-based variant offers genuine fifth-generation stealth credentials.

In addition, the IAF has requested long-term performance data for the Su-57E’s radar-absorbent material (RAM) coatings. Experts within Air HQ have highlighted that the durability and maintainability of RAM under tropical and desert conditions will determine its operational viability in Indian environments. Previous Russian systems have shown limited coating life, leading to maintenance and cost complications.

The service has also pointed to visible inconsistencies in panel alignment and sensor aperture shaping across the Su-57E’s composite fuselage, which contribute to radar scattering. The Air Force considers these imperfections to be critical, given that stealth effectiveness depends on precision manufacturing tolerance — an area still under scrutiny in Russian aerospace manufacturing.

Another major factor under discussion is the long-term sustainment of the Su-57E amid continuing Western sanctions on Russia. IAF is concerned that restricted access to certain avionics, semiconductors, and maintenance components could severely affect aircraft serviceability rates and future upgrade pathways.

These assessments are taking place alongside India’s own fifth-generation Advanced Medium Combat Aircraft (AMCA) development and the ongoing Multi-Role Fighter Aircraft (MRFA) acquisition effort. The IAF leadership has underscored that any potential acquisition must complement indigenous efforts without creating long-term logistic or technological dependencies.

While Moscow continues to pitch the Su-57E as a cost-effective fifth-generation option, New Delhi’s evaluation framework appears to be shifting toward a more pragmatic balance between stealth effectiveness, maintainability, and strategic autonomy. The final decision will likely hinge on whether Russia can demonstrate reliable improvements and verifiable stealth data within the next evaluation cycle.

Based On ZEE News (Hindi) Report