The AOS-H2 was built under a project of the Research and Industry Consortium integrating three universities: the Warsaw University of Technology and its Faculty of Power and Aeronautical Engineering and Faculty of Electrical Engineering and the AGH University of Science and Technology, Kraków, and the Project Leader: Rzeszów University of Technology. The industrial partner of the program was Zakład Szybowcowy “Henryk Mynarski”, a glider factory based in Jeżów Sudecki. The project “Hybrid Propulsion System Based on Hydrogen Fuel Cells in a Light Aircraft” is funded under the “Applied Research III” Program by the National Centre for Research and Development. Prof. Marek Orkisz, Ph.D., D.Sc., Eng., of the Rzeszów University of Technology became the Program Manager.

The AOS-H2 motor glider is built of hybrid polymer composites and is the first in Poland and one of the few in the world to have an electrical propulsion system powered by hybrid fuel cells.

Developing a fuel cell unit powered by compressed hydrogen to be built in on board an aircraft was quite a feat in itself. The innovative fuel cell block with an output of 10 kW that ensures a stable horizontal flight after take-off and climb was developed and produced by the team of the AGH University of Science and Technology, boasting a track record in similar projects. The team worked under the direction of Magdalena Dudek, Ph.D., D.Sc., Eng., a university professor at the Faculty of Energy and Fuels. The fuel cell block built in on board the motor glider is complemented by an auxiliary battery of electrochemical lithium-polymer cells which powers the electronic systems and supports the propulsion system during maximum power consumption, i.e. during the take-off and climb of the motor glider. The total output of the hybrid power system for propulsion is 40 kW. Spare hydrogen compressed to the pressure of 300 bar in two cylinders of 12 liters each provides ca. 60 minutes of continuous work of the propulsion system.

The AOS-H2 airframe was designed at the Warsaw University of Technology, just as its older predecessor, the electric-powered motor glider AOS-71, had been some years before. In both cases, the airframe structure was developed at the Faculty of Power and Aeronautical Engineering, Institute of Aeronautics and Applied Mechanics, under the direction of Wojciech Frączek, M.Sc., Eng. The AOS-H2 project was intended as a continuation of the ULS Program that has been run for many years and involves electromobility efforts at the Faculty of Power and Aeronautical Engineering, i.e. designing and building innovative aircraft fitted with low-emission propulsion technologies. The last completed project was the AOS-71 motor glider fitted with an electric-powered propulsion system integrated in the fuselage and powered by lithium-polymer batteries in the wings.

Compliance with the stringent requirements for hydrogen system fittings was a new challenge in designing the AOS-H2 airframe. Made mostly of carbon fiber reinforced composites, the motor glider structure is a good electrical conductor but it can get electrostatically charged because of the non-conductive adhesive joints in the structure. In addition, the location and installation of individual components had to be designed is such a way in the structural and engineering design so that uninterrupted work of complex electronic systems and the hydrogen system could be ensured. It was also important to provide an adequate level of safety to the pilot during the aircraft operation. Very good and creative collaboration with the Warsaw University of Technology Faculty of Electrical Engineering was a key element in those efforts. Under the AOS-H2 project, all issues related to the development of the power electronic systems supporting the fuel cell and electrical engine as well as their comprehensive control and communication to ensure the expected power flows between the fuel cell, the electrochemical battery and the engine were responsibility of a team headed by Grzegorz Iwański, Ph.D., D.Sc. Eng., a university professor of the Warsaw University of Technology Institute of Control and Industrial Electronics, Department of Electric Drive Systems. The entire sophisticated power flow control system with a very complex architecture proved its reliability in the field tests, providing seamless control of the propulsion system fitted with a two-blade propeller. The chief designer of the power electronic devices was Tomasz Miazga M.Sc., Eng. The overall work on the AOS-H2 motor glider at the Warsaw University of Technology was directed by Piotr Czarnocki, Ph.D., D.Sc., Eng., a university professor of the Faculty of Power and Aeronautical Engineering.

All designed and produced components of both the hybrid power supply system and the complete propulsion system were integrated into the airframe built in the partnering glider factory in Jeżów Sudecki. The airframe was provided by the firm of Mr Henryk Mynarski, the manufacturer of the previous structures of the Warsaw University of Technology, i.e. the PW-5 Smyk and PW-6U gliders. In the next step, the motor glider structure underwent selected bench tests which fully confirmed the designed durability and rigidity of the structure. The static tests, integration work and preparation for field tests of the AOS-H2 motor glider were done at the Rzeszów University of Technology with all project consortium members participating. 

A multifunctional research laboratory operating as a test site for research and implementation of aircraft and unmanned aerial vehicles is being set up at the Warsaw University of Technology’s airfield in Przasnysz. It will be home to research on new sources of zero-emission propulsion for aircraft and more. The AOS-H2 hybrid hydrogen motor glider could be a good example and could complement the ongoing research once the test flight and air tests are completed.

Source and photos: Wojciech Frączek, MSc, Eng., WUT Faculty of Power and Aeronautical Engineering