Researchers at the Indian Institute of Technology Madras have taken a significant stride towards developing a vertical take-off and landing aircraft powered by hybrid rocket thrusters.

The team’s innovative experimentation fused real-time hybrid rocket testing with virtual simulation, allowing the platform to achieve a soft landing velocity. This milestone marks an essential breakthrough in VTOL flight, useful across both aerospace exploration and unmanned aerial vehicle applications.

The study emphasised that touchdown velocity is a vital parameter in ensuring safe vertical descent. The hybrid rocket motor was assessed as a feasible propulsion unit for vertical landing platforms due to its simplicity, safety, and compactness compared to conventional liquid engines.

Hybrid propulsion systems are increasingly favoured in modern aerospace design, combining the advantages of solid and liquid propellants with ease of thrust modulation and safety control.

VTOL systems traditionally rely on complex and high-maintenance propulsion mechanisms. To address these constraints, the IIT-Madras researchers conceptualised a hybrid rocket-based propulsion unit specifically intended to reduce mechanical complexity while enhancing performance reliability. Their objective is to realise an efficient, scalable propulsion solution adaptable to both aircraft and UAV configurations.

The research findings, jointly authored by Professor P.A. Ramakrishna, Dr Joel George Manathara, and Anandu Bhadran, have been published in the International Journal of Aeronautical and Space Sciences. 

Professor Ramakrishna highlighted that vertical take-off and landing capabilities eliminate the need for long runways, thereby enabling operations in remote and rugged terrains. Once commercial readiness is achieved, this technology could transform airborne mobility by decentralising flight operations across smaller hubs instead of major airport installations.

The researchers view this study as a significant precursor in building a proof-of-concept for hybrid rocket-thruster VTOL platforms. Future work is expected to include experiments with landing systems possessing multiple degrees of freedom and autonomous attitude stabilisation. Following this, a comprehensive hardware-in-the-loop simulation phase will evaluate landing performance without presuming stabilised conditions.

A distinctive highlight of IIT-Madras’s work lies in the use of hybrid rocket thrusters for VTOL propulsion—a remarkably novel approach in aerospace propulsion studies. The team has also developed a specialised hybrid fuel requiring only compressed air as the oxidiser, simplifying integration with flight systems and enhancing overall safety. In an industrial context, such a configuration offers compatibility with on-demand UAV and air-mobility platforms.

The research further introduced a sophisticated Hardware-in-the-Loop Simulation framework that integrates a live-firing hybrid rocket motor within the feedback loop.

This setup offers unparalleled accuracy, merging hardware realism with simulation flexibility, thus shortening the transition from conceptual design to functional prototype. It paves the way for faster validation of propulsion control algorithms and throttle-response systems under simulated atmospheric conditions.

Testing confirmed that the hybrid rocket motor can modulate thrust dynamically in response to control system inputs. Using a proportional–integral–derivative (PID) controller and a velocity-tracking algorithm, the team successfully demonstrated velocity regulation with fine precision during landing. Cold and hot flow tests achieved a touchdown velocity as low as 0.66 metres per second using air as the oxidiser, proving the system’s safety and performance viability.

The study’s single-degree-of-freedom model yielded promising results during simulation, providing the foundation for ongoing experiments involving attitude-stabilised, multi-thruster VTOL prototypes. Upon successful validation, this hybrid propulsion-based technology could extend to fixed-wing unmanned systems, offering a transformative path for advanced air mobility and future aerospace applications.

Agencies