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Modular Approach to Hybrid Electric Propulsion Architecture

Periodic Reporting for period 2 - MAHEPA (Modular Approach to Hybrid Electric Propulsion Architecture)

Reporting period: 2018-11-01 to 2020-04-30

Today, hybrid-electric cars are commonplace on European roads, but hybrid-electric aircraft are almost unseen on airports worldwide due to the lack of suitable powertrain components. Hybrid-electric powertrains developed by the automotive sector do not match the low weight and high performance values needed for aircraft installation. They differ also in the approach to reliability. Although designed with very high-quality standards typical of the car industry, in a car the failure of a component is survived by the driver simply pulling over the vehicle. Pilots instead need to land safely, therefore one of the project goals is to develop methods to design and connect hybrid-electric components in such a way to obtain a very reliable hybrid-electric powertrain. Within the scope of project MAHEPA (Modular Approach to Hybrid-Electric Propulsion Architecture) the focus is also placed on the development of new propulsion components suitable to power four-seat type aircraft, or by combining them in a distributed approach, for larger applications up to 19-seat airplanes. These design methods and components will represent the baseline for future environmentally friendly aviation.

Air transport is growing yearly over 4% creating new jobs, new mobility opportunities for citizens and new freight transport routes. The environmental costs however, cannot be overlooked. Although newer, more efficient engines equip recently built aircraft, CO2 and NOx emissions from the aviation sector are a non-negligible contributor of overall transport emissions. Acoustic pollution represents also a point of concern for communities surrounding airports, to the point that small General Aviation airfields face weekend closures when nearby residential suburbs are not separated by a buffer zone. To mitigate aviation emissions, electric propulsion represents a key revolutionary technology. Electric aircraft are quieter because there is no combustion engine noise and the propellers can spin at lower frequencies. When operated on fuel cells or battery power only, they represent truly a zero-emission vehicle for the nearby communities.

The objectives of the MAHEPA project are to develop innovative and lightweight hybrid-electric powertrain components and characterize their performance in flight to assess advantages and drawbacks in a rigorous way. Two variants of hybrid-electric propulsion architecture will be tested in flight: the first charges the batteries using a generator connected to a four-stroke internal combustion engine (ICE), while the second variant produces electric power by converting hydrogen in a fuel cell (FC). Each of the variants is installed in a dedicated four-seat test aircraft and both single-propeller airplanes use the electric motors developed in the project. Besides the component development and testing, another important project objective is the framing of a broader picture by preliminary studying new concepts for 19- and 70-seat hybrid-electric aircraft and their impact on infrastructure, regulations and overall emission reduction in an attempt to provide a holistic view of the revolution hybrid-electric aviation will bring to our society.
In the first period of the project a theoretical framework was developed that allows to model the basic components of a generic serial hybrid-electric propulsion system. These components, called modules, and their connection types, called interfaces, enable the development of different types of hybrid-electric propulsion systems. To validate the methodology, studies were performed on both airplanes developed in the project: the first is the ICE-hybrid, while the second is the FC-hybrid.

In parallel to the novel hardware and software development, several studies were started to frame a broader approach to hybrid-electric aviation. Assuming regional transportation can benefit from a 19-passenger and a 70-passenger hybrid-electric aircraft, research activities started to explore the infrastructure costs and burdens considering both the fast recharge and the battery swap case. Innovative aircraft design tools were developed to assess the economical utility and flight performance of new hybrid-electric 19- and 70-seater aircraft. In particular, tools for sizing novel hybrid-electric propulsion systems and hybrid-electric aircraft at conceptual level were developed and validated using experimental data from literature. In the next reporting period, these tools will be used to develop two design concepts, which will form the reference aircraft to estimate the environmental benefits and economic impact on society of hybrid-electric aviation.

In the second period all systems’ designs have been completed and components have been manufactured and tested. The two aircraft prototypes have been manufactured and are ready to begin ground testing.
The university partners continued with the work on the optimization of the power management and on scalability and market studies. Interesting results have been achieved about the modelling of transport demand and new route scenarios.

Nevertheless, there are delays in the project, mainly in the integration of the components. In fact, the ICE-hybrid powertrain ground testing phase is suffering a total delay of almost one year; this is mainly due to the high complexity of the system, which needed a longer development time than what was predicted. Moreover, during the qualification testing of the electric motor, the freewheel broke two times causing an additional delay. Motor and inverters have been completed one year later than what was predicted in the Grant Agreement.
Last but not least, the COVID-19 pandemic slowed the project pace since for many partners it was not possible to continue the ground testing.
These delays will have an impact on the project, especially in terms of flight test data analysis. However, the consortium is well aware of this and is preparing corrective actions to be taken in the third reporting period.
The MAHEPA project generated know-how on design methods on hybrid-electric propulsion systems. Together with the work currently undertaken in component design development, the project is expected to deliver lightweight and high-energy density components capable of hybridizing General Aviation aircraft. With additional industrialization work beyond the scope of the project, these components can form the basis of a powertrain supply chain for CS-23 category aircraft. Furthermore, by using in-flight testing data, emission analysis and socio-economical estimates, the project will provide a broader view to citizens, regulators, industry, fleet operators and authorities about the benefits of hybrid-electric aviation.