To reduce its impact on the environment and improve the sustainability of its operations, the commercial aviation industry has committed to achieve net-zero air transport emissions by 2050. Among numerous technologies the industry is exploring to help achieve this goal, one that holds promise is hybrid-electric propulsion.

Hybrid-electric propulsion systems, which combine fuel-burning engines with electric motors and batteries, create opportunities to significantly improve aircraft fuel efficiency and lower carbon-dioxide emissions, while also offering potential reductions in maintenance costs. Hybrid-electric propulsion architectures could have broad applicability across different aircraft types, with potential fuel savings ranging from 5 percent in large commercial aircraft, to 30 percent for regional commuter aircraft. These advances in efficiency will also support the growing adoption of sustainable aviation fuels.

High-power and high-voltage applications at altitude come with varying challenges, including materials, design, and testing restrictions. Coupled with operation in a harsh environment and the need to minimize failure rates during flight, novel architectures, including fault-tolerant designs, and novel processes, such as arc detection and HV insulation testing, need to be investigated and developed. Thermal management optimization of hybrid-electric propulsion systems will need to be understood in detail to reduce the overall system weight and maximize fuel savings. System integration understanding will also be critical to reducing cost and improving product manufacturability. Taking these technologies to certifiable standards will require further understanding of end-application requirements, which continue to evolve in the emerging hybrid-electric aviation market space.

Collins Aerospace  is working with sister business Pratt & Whitney Canada  to advance sustainable hybrid-electric propulsion technology for the aviation industry. In collaboration with De Havilland Aircraft of Canada, Collins and Pratt & Whitney are integrating a new hybrid-electric propulsion system into a De Havilland Dash 8-100 flight demonstrator. The demonstrator will be re-engined on one side with a 2 megawatt-class propulsion system that combines a fuel-burning engine from Pratt & Whitney with a battery-powered electric motor from Collins in a parallel hybrid configuration.

The electric motor will provide extra power during take-off and climb, demonstrating around 30 percent better fuel efficiency, compared to existing turboprop engines. (Photo: Collins Aerospace)

Both the engine and the motor will each generate about 1 megawatt of power for a 50/50 power split. The engine will be optimized for cruise efficiency, while the electric motor will provide extra power during take-off and climb, demonstrating around 30 percent better fuel efficiency, compared to existing turboprop engines.

Typically, a regional turboprop aircraft, like the Dash 8, requires high take-off power to carry large payloads, but flies relatively slowly under relatively low power. The demonstrator will leverage this large ratio between peak power and steady-state power to create significant total energy savings. The electrical assist is high power and short duration, allowing the size and weight of the energy storage device to be manageable within the aircraft maximum take-off weight.

The hybrid-electric system increases the aircraft’s operating empty weight (OEW), effectively reducing the aircraft’s fuel capacity to allow for the electrical equipment and energy storage. Based on current assumptions of battery energy density and considering the more efficient hybrid-electric system, the re-engined aircraft would have a shorter range compared to the base regional turboprop range of 1,000 nautical miles. Given that most regional turboprop missions are shorter than 500 nautical miles, however, and that the hybrid-electric system could improve fuel economy by 30 percent, the trade-off in range makes technical and economic sense.

Hybrid-electric propulsion systems hold clear potential to reduce aircraft carbon-dioxide emissions and support the industry’s drive toward greater sustainability in aviation. Although this technology is still in development, progress is quickly being made. For the Dash 8 demonstrator, Pratt & Whitney and Collins are targeting ground testing in 2022, followed by flight testing in 2024.

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