Hybrid-Electric Helicopter Propulsion System Safety Analysis

Abstract

As industries are trying to decrease their carbon footprint, new technologies are being implemented. This is also the case for the helicopter industry. Similarly to the automotive industry, the helicopter industry is looking to implement hybrid-electric propulsion. To support this, a lot of research has been conducted into the performance of the different hybrid-electric propulsion systems architectures.
However, no effort has been made to map the effects these architectures have on the safety of thehelicopter. Since safety is an important aspect of helicopter design, being able to grasp the effect ofvspecific architectural choices early in the development process could provide a major benefit in terms of development time. This knowledge gap led to the research goal addressed with this study: How is the risk analysis for helicopters affected by hybrid-electric engine architecture?

The safety assessment conducted during helicopter development is mandated via several industry standards, most notably SAE ARP 4754 and SAE ARP 4761. These standards were followed while performing a safety assessment for a baseline architecture provided by the thesis company. The first step was to identify the exact scope of the hybrid-electric propulsion system, explicitly determining which subsystems are considered part of the hybrid-electric propulsion system. The next step was the identification of the different functions that the system has to perform. By analyzing how these functions can fail several failure conditions could be specified. The failure conditions were then dissected until the failures could be traced to sub-system level failures. The knowledge gained from this analysis was then used to create a baseline to compare other theoretical architectures. The concepts were compared by failure rates for 5 different failure conditions, system weight, engine development requirements and
system complexity.

4 main classes of hybrid-electric propulsion system architectures were studied:
• Double-shaft Parallel
• Single-shaft Parallel
• Series-Parallel
• Series

Overall, it was found that choices in hybrid-electric propulsion system architecture significantly impact the safety assessment of helicopters. From the classes mentioned above, double-shaft parallel architecture has the least disadvantages, closely followed by single-shaft parallel. Series-parallel has higher failure rates but still shows a realistic possibility of implementation. Of all the architecture classes, the series architecture shows the worst results in all comparisons, lacking realistic implementation possibilities.

By combining this study with pre-existing performance studies and the recommended study on system weight, a comprehensive overview can be created to aid helicopter architects in the early developmentstages.