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The trend of powertrain electrification is quickly spreading from the automotive field into many other sectors. For ultra-light aircraft, needing a total installed propulsion power up to 150 kW, the combination of a specifically developed internal combustion engine (ICE) integrated with a state-of-the-art electric system (electric motor, inverter and battery) appears particularly promising. The dimensions and weight of ICE can be strongly reduced (downsizing), so that it can operate at higher efficiency at typical cruise conditions; a large power reserve is available for emergency maneuvers; in comparison to a full electric airplane, the hybrid powertrain makes possible to fly at zero emissions for a much longer time, or with a much heavier payload. On the other hand, the packaging of a hybrid powertrain into existing aircraft requires a specific design of the thermal engine, that must be light, compact, highly reliable and fuel efficient.

This paper focuses on the key problem of future aeronautics: which relates on energy efficiency and environmental footprint on a scientific point of view. Reducing emissions and increasing the energy efficiency would be both a key element to propel the market and increase the diffusion of personal aerial transport against ground transportation. Novel vehicle concepts and systems will be necessary to propel this innovation which could revolutionize our way of moving. This paper approaches an energetic preliminary design of a vehicle concept which could fulfill this social and cultural objective. Low cost energy efficient vehicles, which could be suitable for personal use with a high economic efficiency and without needs of airports, seem actually a real dream. Otherwise, is it a feasible goal or a scientific dream? Otherwise, a design method based on first and second law and thermodynamic and constructal law could allow reaching those goals.

Rotocycloid propulsion presents interesting performance as a possible long-term alternative to helicopters in a far future. It will lead to increase the energy efficiency of VTOL vehicles. This paper focuses on optimization of an airship with the possibility up to 2000 h/year of photovoltaic propelled flight at a cruise speed about 20 m/s. This paper demonstrates the feasibility of this airship concept and presents a full dimensioning according to the CDE (Constructal Design for Efficiency) developed at University of Modena and Reggio Emilia. The proposed solution has been deeply analyzed and the analysis of performances has been presented. The results allow thinking to a novel class of vehicles designed specifically to take the maximum advantage by this propulsion method.