Earlier this week, Rolls-Royce began ground testing an aircraft hybrid electric propulsion system in which a gas turbine engine generates the electric power used for thrust.
Rolls-Royce plans to implement its new hybrid electric system in Airbus’s E-Fanx demonstrator aircraft in 2020. The latest ground-tested demonstrator used Rolls-Royce’s M250 gas turbine engine, which provides between 500 kilowatts and 1 megawatt.
The new propulsion system has three different modes: series hybrid, parallel hybrid, and turbo-electric mode. Each of these has different levels of utilization for the aircraft’s onboard battery. In series hybrid, the turbine engine charges a battery which then provides power for thrust. In parallel hybrid, electric power is provided by a combination of the battery and the turbine, and in turbo-electric, electricity produced from the turbine flows directly to the motors.
Note that in all of these modes, power is provided to electric motors which then provide thrust. This means that although the system uses a gas turbine to provide electricity, all thrust providers are electric.
The Rolls-Royce, Siemens, and Airbus E-Fan X hybrid electric flight demonstrator planned for 2020:
Many eVTOL vehicles on the market are already using hybrid electric systems rather than pure electric, because battery technology with higher ranges can add great amounts of weight. Some of the vehicles that plan on using hybrid electric systems include the Dufour aEro2, the Workhorse SureFly, the AirspaceX Mobi-One, the XTI TriFan 600, the Transcend Air Vy400, and the Bell Nexus air taxi.
Rolls-Royce envisions that its new propulsions system will be used by eVTOLS, hybrid helicopters, and even general aviation hyrbid aircraft. New aircraft developers including Zunum Aero and Voltaero (founder John Botti was recently featured on the TransportUP Podcast) have also already begun developing aircraft that use hybrid electric propulsion, showing its high potential for the future. Other companies working on hyrbid or complete electric systems include magniX, which specializes in electric motors, and Verdego Aero, which specializes in propulsion systems specifically for eVTOL.
Why it’s important: While some eVTOL companies plan on using total electric systems, others that aim at higher ranges are looking to the kind of hybrid electric systems being built by Rolls-Royce. While there is certainly a market for short-range intracity travel, eVTOLs that aim at further distance intercity ‘regional air mobility‘ will require hybrid electric systems.
Sources // Flying Magazine