Hindustan Aeronautics Limited is moving to a five-bladed articulated rotor system for its upcoming Indian Multi-Role Helicopter (IMRH), marking a clear shift from the hingeless rotor design used on the Advanced Light Helicopter Dhruv and the Light Combat Helicopter. This transition reflects the far greater load-bearing and performance demands of a 13-tonne medium-lift platform compared to lighter utility and attack helicopters.
While hingeless rotors have proven efficient for smaller aircraft, the IMRH’s higher weight and mission profile require a stronger structural approach capable of managing intense aerodynamic forces and complex flight conditions. Designed to replace the Mil Mi-17 fleet of the Indian Air Force, the IMRH must handle significantly higher bending moments at the rotor root during heavy-lift missions, aggressive maneuvers, and turbulent operations. Hingeless systems would demand thicker, heavier blade roots, reducing efficiency, whereas articulated rotors use flapping and lead-lag hinges to dissipate stress loads more effectively.
The shift from a four-blade to a five-blade configuration increases rotor disc area, enabling higher lift generation without substantially enlarging rotor diameter, which is expected to remain around 21.2 meters. This design improves load distribution, enhances lift efficiency, and reduces vibration transmitted to the fuselage—critical for troop transport and VIP roles where comfort and structural longevity are essential.
Articulated rotors also offer smoother control responses, favoring stability and load management over agility—an approach consistent with global heavy-lift platforms such as the Sikorsky S-92 and other helicopters in the 10+ tonne class. The IMRH is expected to operate in demanding conditions, including high-altitude and high-temperature environments, where structural reliability is crucial.
For the naval variant, the Deck-Based Multi-Role Helicopter (DBMRH), the articulated rotor design also simplifies integration of blade-folding mechanisms required for shipborne operations. This makes it better suited for maritime use compared to rigid hingeless systems. Overall, HAL’s decision represents a strategic evolution in rotorcraft design, shifting from agility-focused configurations toward robust, heavy-lift optimized engineering.
