Researchers from the Indian Institute of Technology Madras (IIT Madras) have made significant progress toward creating a Vertical Take-off and Landing (VTOL) aircraft and unmanned aerial vehicle (UAV) utilizing hybrid rocket thrusters. Their innovative study combined real-time testing of a hybrid rocket engine with virtual simulations, successfully achieving the required velocity for a soft landing, which is a vital aspect for various applications, including planetary exploration and terrestrial landings.
The focus of the research was to assess the practicality of hybrid rocket motors for vertical landing platforms, highlighting their advantages over traditional liquid engines in terms of simplicity and safety. Hybrid rocket systems are increasingly favored due to their enhanced safety features and controllable thrust capabilities, merging the best aspects of both liquid and solid rocket propulsion systems.
Currently, the complexity and maintenance demands of existing VTOL systems present challenges. Consequently, the researchers proposed a hybrid rocket thruster-powered platform as part of a developmental study aimed at creating an efficient propulsion system for VTOL applications in aircraft and UAVs. The research findings were documented in a paper co-authored by Prof PA Ramakrishna, Dr Joel George Manathara, and Anandu Bhadran, published in the International Journal of Aeronautical and Space Sciences.
Prof Ramakrishna, from the Department of Aerospace Engineering at IIT Madras, emphasized the importance of VTOL technologies by stating, “Vertical take-off and landing, as the name suggests, will enable an aircraft to take off and land vertically, eliminating the need for infrastructure like long runways.” This capability enhances access to remote and challenging terrains where traditional runways are impractical. He noted that while helicopters are currently utilized in such areas, they are limited in speed, range, and efficiency compared to fixed-wing aircraft.
He added, “Once the VTOL system reaches the Technology Readiness Level (TRL) for commercial application, it will be a game-changer in both civil and military aviation. VTOL will help decentralize air transport to multiple locations rather than a single large airport or airbase, providing significant strategic and operational benefits.” This research serves as an initial step toward developing and demonstrating a proof-of-concept for a hybrid rocket-powered VTOL platform.
Discussing the practical implications of the research, Prof Ramakrishna mentioned that future studies could involve experimental trials of the landing platform designed with multiple degrees of freedom. He stated that achieving attitude stabilization of the platform would enable further hardware-in-the-loop simulations for landing that do not assume a stabilized attitude system, moving closer to realizing a VTOL platform with hybrid rocket thrusters.
Dr Manathara, an Associate Professor in the Department of Aerospace Engineering at IIT Madras, highlighted the uniqueness of this research, noting that the use of hybrid rocket thrusters for VTOL applications is both novel and innovative. He remarked, “Our work paves the way to move beyond conventional approaches by demonstrating the viability of hybrid rocket propulsion, which offers a balance of safety, simplicity, and control.”
A notable advancement is the development of hybrid rocket fuel that utilizes only compressed air as an oxidizer, simplifying the integration of VTOL systems with aerospace vehicles, particularly in environments where compressed air is available. Dr Manathara further explained the significance of the unique Hardware-in-the-Loop Simulation (HILS) framework developed by the researchers, which combines physical testing with simulations, providing a cost-effective method for rapidly developing complex systems.
In this innovative approach, rather than typical setups involving servo motors or microcontrollers, the research team integrated a live hybrid rocket motor into the HILS loop, enhancing the accuracy of their testing framework and bridging the gap from technology to functional prototype. This advancement brings them closer to practical applications.
Researcher Anandu Bhadran noted that hybrid rocket motors have been regaining interest for their controllable thrust capabilities. Previous studies established closed-loop thrust control for their hybrid rocket motor, which was tested within the HILS framework to evaluate the feasibility of a vertical soft landing. The hybrid rocket motor demonstrated a dynamic response to thrust demands dictated by a guidance control algorithm.
In the hot flow tests, the system achieved a touchdown velocity of 0.66 m/s, meeting safety objectives with air as the oxidizer. The HILS simulation approach enabled a series of cold and hot flow tests in a simulated VTOL environment, facilitating the fine-tuning of a PID controller for a seamless landing. The developed landing algorithm, which incorporates a velocity-tracking mechanism and a PID controller, proved effective in monitoring and adjusting the velocity profile for safe landings.
The successful outcomes of the HILS simulation have set the stage for future experimental studies involving a landing platform with multiple degrees of freedom. Efforts are ongoing to achieve attitude stabilization in the experimental VTOL platform, with subsequent simulations planned that do not rely on a stabilized system. This next phase will further advance the realization of a hybrid rocket thruster-powered VTOL platform.
