Electric Aircraft: What"s Needed To Make The Dream A Reality?

Achieving the desired power and range can make electric aircraft a near-term reality.


Photo: Aura Aero

With the ever-increasing need to shift towards sustainable transport, small and large manufacturers are exploring the feasibility of electric transport aircraft. Manufacturers, along with their research collaborators, aim to offer an aircraft that achieves sustainable transportation for passengers and cargo with zero carbon emissions.

Electric Aircraft

In the past few years, there have been tremendous advances in making zero-carbon commercial transport a reality. Numerous all-electric and hybrid-electric aircraft have either been launched or are in the prototype phase. In most existing examples, though, electric aircraft technology is limited to remotely piloted aircraft. While an unmanned electric vehicle sufficiently achieves zero-emission flights, it has minimum load and range capabilities.

In order to make the electric aircraft dream a reality for commercial passenger service, a significant increase in power and range must be achieved. This is done by improving the efficiency of the electrical power system. While the usable efficiency of the electric motor itself is over 90% (significantly greater than fuel-powered engines), the supporting power source (battery or sustainable fuel) lacks efficiency. For example, the Extra 330LE aircraft with a Siemens-powered engine returns a maximum of 20 minutes of flight, including takeoff and landing.

Alternate power sources

The concise flying range achieved by battery-driven electric aircraft remains the biggest challenge. Thousands of kilograms of battery packs are required to achieve a considerable flying range to fulfill desired passenger and cargo flights. One liter of lithium-ion battery pack stores 20 times less energy than one liter of jet fuel. Moreover, unlike consumable fuel, the battery weight stays constant throughout the flight.

Is the hybrid-electric system the way to the future?

Large OEMs, including Airbus, Rolls-Royce, and Raytheon, are proposing hybrid-electric aircraft as a solution to sustainable transportation. Rolls-Royce was recently awarded Ђ4.6 million from the government of Hungry to support the development of hybrid-electric aircraft. Rolls-Royce has successfully designed its first hybrid-electric propulsion system to power its High Power High Scalability Aircraft Hybrid Powertrain (H3PS) 4-seater aircraft, which completed its first successful test flight in December 2021.

In a hybrid electric aircraft, battery packs supply power to the electric motor, and a combustion engine generator provides power by burning fuel. Unlike traditional gas turbine engines, where the propulsive power comes from the exhaust air, a hybrid engine generator feeds energy to the electrical motor and the battery. As a result, the motor drives the fan or propeller.

Propulsive gains of hybrid aircraft

In a hybrid electric efficiency chain, there is a generator core, an electrical motor, and an inverter to provide suitable current to the motor. The efficiency of a superconductor generator is approximately 98%, and the efficiency of an electrical motor is 95%.

Switching to advanced semiconductors can substantially increase the inverter efficiency. For example, silicon-carbide (SiC) based semiconductors increase the breakdown electric field strength by tenfold. Assuming minor system losses, the chain efficiency of a typical hybrid electrical system can be approximately 94%. This is the percentage of total available energy that can be converted into useful work (to run a fan or a propeller).