The HYPSTAIR project, which began in September 2013 and officially ended in February 2016, has designed a serial hybrid propulsion system for small aircraft that uses an electric motor to drive the propeller. The electrical power can be sourced either from a battery pack, that can be recharged during the flight, or from an on-board fuel powered generator. Project researchers have designed the hybrid propulsion system’s components from the conceptual stage. The components have been sized and designed considering the performance and energy efficiency of the complete airframe-propulsion system and the finished prototype engine has recently been tested for the first time in Ajdovcscina, Slovenia. The plane chosen for the first test flight was provided by Pipistrel, the Slovenian light aircraft manufacturer that has coordinated the project. All of the powertrain components were developed by fellow project consortium member Siemens, a global leader in electric propulsion. New hybrid specifications For the initial testing, a five-blade, low-rpm propeller was attached to the motor. The first power-up tested all power modes at low and high power settings. Additionally, all of the components were designed with all existing aviation safety and certification regulations in mind. The HYPSTAIR project’s 200 kW motor is the most powerful hybrid electric powertrain developed for aviation to date, providing an equivalent amount of power as typical aviation engines. The HYPSTAIR drive motor is designed to deliver 200 kW for takeoff and 150 kW in cruise. The motor can run in electric-only mode, using battery power, generator-only mode or hybrid mode combining the two. Whilst the HYPSTAIR tests have been highly promising, the current limitations of electric energy storage technology make an electric-only propulsion system unsuitable for long distance flying. Consequently, an on-board generator provides a weight efficient, if somewhat less energy efficient, power generation solution. To realise a highly capable hybrid propulsion system, the electric motor and generator have been designed with special emphasis on high power densities to reduce the weight of the propulsion system. This thus maximises the airplane’s payload. Special attention was also given to the component’s efficiencies in order to realise the potential for increased energy efficiency. Tailored Graphic User Interface (GUI) The project has also developed a tailored Graphic User Interface (GUI) for hybrid drives following extensive tests and simulations. They comply with customs and regulations for the display of information in aeronautics, but bring innovations through the use of systems and regulations from other fields (automotive and marine). The new GUI has been designed in a way that is familiar to professional pilots in a layout similar to the analogue instrumentation. This type of representation and layout can particularly help pilots from older generation aircraft (that have lower levels of computerisation) or those with poor training on digital systems. As such, the design of the human-machine interface has emphasised simplicity and a high level of automation that will reduce the pilot’s workload. The design places emphasis on the pilot being able to receive important information on the state of the hybrid system through visual and haptic cues. Overall, the project hopes that such its innovative interface system will be adopted as standard by the aviation industry. Next steps With the end of the project, the aim is to begin installation of developed components into a flying airframe that will pave the way for the commercialisation of a hybrid drive airplane. Furthermore, the components developed during the project, as well as obtaining the necessary certification standards, would also allow other airframe and electrical component manufacturers to enter the market of hybrid and electric propulsion aircraft. The success of the project would therefore help to open a completely new aviation market. The EU could have a clear market advantage by not only defining the standards but also pioneering the first designs specifically tailored for this market.