At Pipistrel, we are announcing successful completion of the first stage of the project UNIFIER19, where three project partners (Politecnico di Milano, TU Delft and Pipistrel Vertical Solutions) have laid groundwork methodology and tools for multi-objective interdisciplinary design and optimization of a brand-new near-zero-emission regional aircraft concept.

Pipistrel’s ambition is to develop and demonstrate a  zero emission 19-seat commuter aircraft to provide fully climate neutral aerial mobility in the next decade. By using hydrogen-based propulsion a 100% emission reduction is expected. Apart from the emission reduction potential on the aircraft level, the aircraft will present a stepping stone for using zero emission technology on larger platforms such as the Regional and SMR aircraft. In a future scenario, the 19-seat zero emission aircraft could replace larger conventional/non-zero emission aircraft leading to an increased positive climate impact and improved mobility for EU citizens.

For millions who drive to work every day, travelling along highways and encountering heavy traffic is typically something to be endured and rarely something to enjoy. Funded under EU Clean Sky 2, the new UNIFIER19 airliner concept design will offer a new, sustainable and cost-efficient air mobility solution. The 19-passenger near-zero-emission aircraft is designed to provide a diffused service connecting smaller airports to each other (miniliner) and with hubs (microfeeder), accommodating both scheduled and on-demand shuttle flights. Exploiting the sparse, underused European small airport network (Figure 1), UNIFIER 19 will offer commuters a radically new mobility experience that will be as simple to use as a bus.

Figure 1: Trans-European Transport Network, with hub airports are indicated as white aircraft silhouette in black circles; airports capable of 20-70 passengers aircraft indicated as black aircraft silhouettes.

Both aircraft roles (miniliner and microfeeder) are conceived as key components in the future development of a more connected European transportation network through enhanced, environmentally sustainable regional air travel.

The multi-objective interdisciplinary optimization will explore a vast design space, considering all possible combinations of aero-propulsion systems (blended wing body, distributed electric propulsion, wingtip propellers, box-wing, …) (Figure 2) and hybrid-electric architectures (lithium batteries, internal combustion engines, fuel cells, liquid hydrogen systems, …) (Figure 3).

Figure 2: Schematics of zero-emission powertrains (top: pure electric, bottom: FC serial hybrid-electric)

Figure 3: Examples from aero-propulsion design space (Hoogreef M., et al: “Synthesis of Aero-Propulsive Interaction Studies Applied to Conceptual Hybrid-Electric Aircraft Design”, AIAA Scitech Forum, 2020)

Moreover, optimization will include chemical and noise emission footprint objectives (Figure 4), as well as appropriate production and operating cost indicators, developed exclusively for the project (Figure 5). In this way, UNIFIER19 will offer a fast, affordable transport solution with low noise footprint and near-zero impact to the environment.

Figure 4: L. Gasco, C. Asensio and G. de Arcas: “Communicating airport noise emission data to the general public,” Science of The Total Environment, vol. 586, pp. 836-848, 2017.

Figure 5: Contribution of each cost in the total direct operating cost for the typical mission of the reference aircraft.


Initially, the project was set to consider optimization to combustor-based propulsion as well as entirely new propulsion technologies. Already in this first stage of the project it became very clear, that the only responsible, sensible and sustainable way for European aviation for REGIONAL air-traffic to be embraced is going towards complete zero-emission flight. This is why the project major focus will be on hydrogen and battery-based propulsion for the well-being of European citizens, the promotion of the world-leadership of European Aerospace Industry, and to pave the way for future research, innovation actions and developments under Clean Sky 3.

The design concept (Figure 6), as the final project outcome, will be a keystone for enabling Europe’s Flightpath 2050 vision, which envisages that virtually all EU citizens shall reach any continental destination in less than four hours, door to door, by the year 2050.

UNIFIER19 - miniliner/microfeeder

Figure 6: Artistic impression of a 19-seater with liquid hydrogen hybrid propulsion technology (based on preliminary sizing evaluation)


Clean Sky 2

The project leading to this application has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No [864901].

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