Indian news agency ANI, quoting defence officials, recently reported that the Kaveri Derivative Engine (KDE) for the Ghatak UCAV is undergoing trials at Russia’s Gromov Flight Research Institute (GFRI), with 25 hours of testing still pending.
The GFRI is a prominent Russian aerospace research and testing center located in Zhukovsky, near Moscow.
It operates an aircraft test base known as Ramenskoye Air Base and has been involved in numerous significant aerospace projects, including hosting the MAKS International Air Show and serving as a backup landing site for the Buran space shuttle program.
KDE Readiness For Flight Testing
On December 23, 2024, India’s GTRE announced that the KDE had been cleared for in-flight testing.
The KDE was scheduled for 70 hours of flight testing on a specially modified Russian Ilyushin Il-76 aircraft starting in February 2025. The Il-76 has been adapted to integrate the KDE engine with its fuel and engine management systems.
The flight trials aim to evaluate the KDE’s efficiency at high altitudes.
Flight Testing Delays
Flight testing appears to be progressing more slowly than desired by the GTRE. The likely cause is Russia’s other flight testing commitments.
Russia is simultaneously flight-testing several new aero engines to revive its civil aviation sector, which has been hit hard by Western sanctions. For instance, the PD-8 turbofan engine is being tested for the SSJ NEW airliner, a 100% import-substituted version of the SSJ-100.
Before flight testing began, the KDE had completed over 140 hours of testing, including 70 hours of ground tests at GTRE’s Bangalore facility and 75 hours of altitude tests in Russia.
It was previously reported that a team of 20 GTRE scientists would collaborate with Russian experts to ensure the success of the flight trials.
Kaveri Derivative Engine (KDE) Evolution
The KDE is derived from the Kaveri GTRE GTX-35VS engine, originally designed for India’s Light Combat Aircraft (LCA) Tejas. Unlike the GTX-35VS, the KDE is a non-afterburning engine, tailored for UCAV applications.
Building on the core of the original Kaveri engine, the KDE incorporates advanced materials, aerodynamics, and cooling technologies for improved performance. It is expected to produce 48 kN of dry thrust, slightly lower than the GTX-35VS due to modifications for UCAV applications.
GTRE has also developed a new fan designed for high inlet pressure distortion tolerance, targeting future stealth airframes with serpentine intakes. The objective is a 3.4:1 pressure ratio and 78 kg/s mass flow in a three-stage design, optimized for stealthy platforms.
At Aero India 2019, GTRE displayed a model of a Kaveri engine compatible with serpentine air intakes.
The DRDO plans to develop various KDE variants to meet the evolving requirements of Unmanned Combat Aerial Vehicles (UCAVs). If necessary, an afterburner will be integrated to increase thrust to 73–75 kN for more demanding applications.
Technological Stature Of Kaveri Engines
The Kaveri Core is classified as a fifth-generation engine. Aero engines are often classified based on their Turbine Inlet Temperature (TIT)—the temperature of gases entering the first stage of the turbine.
Higher TIT enables higher efficiency and thrust but requires advanced materials and cooling techniques.
Here’s a general TIT classification by generation:
1st Gen (1940s) ~1,100 K
2nd Gen (1950s-60s) ~1,250 K
3rd Gen (1970s) ~1,400 K
4th Gen (1980s) ~1,600 K
5th Gen (1990s-2000s) ~1,750 K
6th Gen (2020s+, Adaptive Engines) ~1,800-2,000 K
The GTX-35VS has a TIT of approximately 1,427°C (2,600°F or 1,700 K)—slightly lower than contemporary engines like the GE F414 and Eurojet EJ200, which operate at 1,700–1,800 K.
The KDE is expected to have a similar or slightly reduced TIT due to the absence of an afterburner, but specific TIT values for the KDE have not been publicly disclosed.
GTRE continues to work on enhancing the Kaveri engine’s performance through the development of advanced materials and cooling techniques.
Flight Testing of GTX-35VS
The GTX-35VS Kaveri engine was flight-tested at the Gromov Flight Research Institute (GFRI) from November 2010 to mid-2014. The first flight occurred on November 4, 2010, using a modified Ilyushin Il-76 as the flying testbed.
The engine underwent 27 test flights, accumulating over 57 hours of runtime in various flight conditions.
During testing, the Kaveri engine demonstrated a dry thrust of 49.2 kN against the design target of 51 kN. However, the thrust deficit was more significant with afterburner: 70.4 kN achieved vs. 81 kN designed.
In addition, the engine exceeded the ASR weight limit of 1,100 kg by 135 kg.
Indian scientists developed nine engine prototypes and four core engine prototypes, collectively accumulating over 2,550 hours of testing.
Due to the dry thrust shortfall, it was decided to develop a variant of the GTX-35VS for UAV applications, such as the Ghatak stealth UCAV, which primarily requires dry-thrust-only engines to minimize heat and noise signatures. UCAV thrust requirements are also generally more modest.
As stated earlier, DRDO plans to integrate an afterburner into the KDE if higher thrust—73–75 kN—is needed for future applications, while continuing to improve the engine’s overall characteristics.
Conclusion
In 2018, the Kaveri engine passed a Safran audit, confirming it had reached a maturity level suitable for limited aircraft integration.
Despite delays, cost overruns, and performance shortfalls, a clear pathway exists for the continued development of the Kaveri core. The initial focus is on meeting UCAV requirements, with the long-term goal of generational leaps in engine technology.
With aggressive funding and technology partnerships, there is no reason why a future Kaveri variant could not power a next-generation Indian stealth fighter.
Interestingly, India approved the development of an advanced fighter jet prototype, the latest push to boost local arms development.
Indian Defence Minister Rajnath Singh approved the prototype of a 5th generation Advanced Medium Combat Aircraft (AMCA), the ministry said in a statement, calling it a “significant push towards enhancing India’s indigenous defence capabilities”.
India’s Aeronautical Development Agency (ADA) — a government agency under the Ministry of Defence responsible for aircraft design — is “set to execute the programme through industry partnership,” it added.
“This is an important step…which will be a major milestone towards aatmanirbharta (“self-reliance”) in the aerospace sector”.
- Vijainder K Thakur is a retired IAF Jaguar pilot, author, software architect, entrepreneur, and military analyst.
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