Why the Tejas MkII Lacks DSI Intakes While AMCA Incorporates Them

India’s defense aviation sector is on an ambitious trajectory, spearheaded by projects like the Tejas MkII Medium Weight Fighter (MWF) and the Advanced Medium Combat Aircraft (AMCA). These aircraft represent a critical leap in the country’s push for self-reliance in defense manufacturing. However, a key difference between the two jets has sparked interest among defense enthusiasts and experts: the inclusion of Diverterless Supersonic Inlets (DSI) in the AMCA and their absence in the Tejas MkII. This design decision reflects a nuanced balance between technological priorities, cost considerations, and operational goals.

What Are DSI Intakes, and Why Are They Important?

Diverterless Supersonic Inlets are an advanced intake design that eliminates the need for traditional diverter plates and bypass ducts. The primary advantages of DSIs are:

1. Reduced Radar Cross-Section (RCS): By eliminating complex external components, DSIs improve an aircraft’s stealth capabilities by reducing radar reflectivity.
2. Improved Aerodynamics: DSIs create smoother airflow into the engine, reducing drag and increasing efficiency.
3. Simplified Maintenance: Fewer moving parts mean lower maintenance demands and a lighter overall structure.

These benefits make DSIs particularly desirable for stealth-focused, next-generation fighter jets. Yet, despite these advantages, their incorporation involves significant design complexity, which influences their suitability for different platforms.

Why the Tejas MkII Doesn’t Feature DSI Intakes

The Tejas MkII is an evolutionary upgrade of the Tejas MkI and MkIA. Retaining a design lineage from its predecessors, the MkII integrates advanced avionics, a higher payload capacity, and better performance parameters. However, it doesn’t adopt DSIs for several practical reasons:

1. Inherited Airframe Design:
   The MkII is built on the existing Tejas airframe to save on development costs and time. The conventional intake design of its predecessor was retained and optimized for the MkII’s operational needs, which focus less on stealth compared to 5th-generation fighters. Introducing DSI technology would have necessitated a complete re-engineering of the airframe, leading to delays and budget overruns.

2. Focus on Operational Priorities:
   The primary objectives for the Tejas MkII include enhanced maneuverability, greater payload capacity, and improved avionics. These upgrades cater to the operational requirements of a 4.5-generation fighter. Stealth was an enhancement, not the central focus, for the MkII’s design philosophy.

3. Timeline and Budget Constraints:
   The Tejas MkII is critical to the Indian Air Force’s fleet modernization and is intended for quicker induction. Incorporating DSIs, which require extensive aerodynamic testing and validation, would have delayed the program significantly.

4. Stealth Requirements:
   While the Tejas MkII features some stealth improvements—such as radar-absorbing materials and a reduced frontal RCS—it doesn’t demand the same level of stealth optimization as a 5th-generation aircraft. The traditional intakes meet the stealth and performance needs of the MkII without requiring the leap to DSIs.

Why AMCA Features DSI Intakes

In contrast, the AMCA is designed from the ground up as a 5th-generation fighter, with stealth as a cornerstone of its design. Here’s why DSIs were chosen for the AMCA:

1. Stealth-Driven Design:
   As a stealth-centric platform, the AMCA incorporates multiple technologies to minimize RCS, such as internal weapon bays, radar-absorbing coatings, and DSIs. The elimination of external diverters and bypass ducts significantly reduces radar visibility.

2. Clean-Slate Approach:
   Unlike the Tejas MkII, the AMCA doesn’t inherit its design from an earlier platform. This freedom allowed designers to integrate DSIs and other advanced features from the outset without retrofitting existing structures.

3. Future-Proofing:
   The AMCA is being developed to compete with global 5th-generation fighters, including the F-35 and the Chinese J-20. Incorporating DSIs positions it as a technologically advanced competitor, catering to both stealth and aerodynamic efficiency.

4. Longer Development Timeline:
   The AMCA’s development schedule, while ambitious, allows room for integrating cutting-edge technologies like DSIs. Unlike the Tejas MkII, the AMCA program isn’t under the same time pressure for immediate deployment.

Strategic Balance in Design Philosophy

The absence of DSIs on the Tejas MkII and their inclusion in the AMCA highlight the distinct roles these aircraft are designed to play. The Tejas MkII prioritizes affordability, ease of production, and rapid deployment to fulfill the IAF’s immediate needs. On the other hand, the AMCA embodies India’s long-term vision of fielding a world-class stealth fighter capable of rivaling global competitors.

By avoiding the complexity of DSIs on the MkII, India has ensured faster delivery and broader affordability for the IAF. At the same time, the integration of DSIs into the AMCA signifies a leap toward advanced capabilities and technological parity with global aviation leaders.

This thoughtful division of priorities reflects India’s pragmatic approach to defense aviation, balancing current operational needs with future aspirations. The decisions made in these programs not only serve immediate requirements but also lay the foundation for the evolution of indigenous aircraft design.