Benefits of Parallel Hybrid Electric Propulsion for Transport Aircraft

As battery and electric machine technologies improve, the electrification of aircraft propulsion systems may have the potential to reduce the energy consumption and emissions of transport aircraft. Incorporating electrical components adds a dimension to the propulsion system design space and introduces new tradeoffs between weight and efficiency. In this article, we apply numerical optimization to the conceptual design of regional transport category airplanes to quantify the energy efficiency benefits of parallel hybrid electric propulsion, identify the mechanisms of the benefits, and characterize the scaling effects of design parameters such as range and electrical technology parameters such as battery specific energy. The results show that the state-of-the-art technology may provide energy savings up to 1%–8% over conventional turboprop engines, while projected improvements in electric technology may allow greater savings of up to 14%, albeit at a reduced range relative to conventional gas turbine-powered aircraft. By supplementing the gas turbine engine with electrical power in high-thrust conditions, the overall efficiency of the propulsion system can be improved throughout the mission. Improvements in battery specific energy and power electronics specific power are identified as enablers for efficient hybrid electric aircraft propulsion.