A mix of technologies substantially improves the range of electric aircraft.
With the ever-increasing interest in minimizing our carbon footprint in aviation, companies, big and small, are keen to develop electric aircraft. Aircraft manufacturers aim to offer a sustainable mode of future transportation for passengers and cargo with zero carbon emissions.
The industry’s decarbonization mission requires the use of various technologies. These include significant improvements in infrastructure and operations, the use of sustainable aviation fuel (SAF), and the use of parallel power technologies.
Current advancements in electric aircraft research have opened doors for small human-piloted aircraft. One of the challenges of battery-driven electric aircraft is its concise range. Thousands of kilograms of battery packs are required to achieve a considerable flying range to fulfill passenger and cargo demand between two locations.
Hybrid electric aircraft
Hybrid electric aircraft provide a relatively feasible solution where a substantial range is achieved while minimizing carbon emissions. 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 significant portion of the propulsive power of a hybrid vehicle comes from an electric motor. The label “hybrid technology” is often misused when only small amounts of power are gained from an electrical motor.
For example, even when the engine’s starter generator is used to power an electrical system, it technically uses hybrid technology. But a true hybrid aircraft is where an electric motor is substantially involved in powering the thrust-producing part, the propeller or fan.
Serial hybrid system
A serial hybrid system is based on battery packs that have a limited range. The flying time or endurance of the aircraft typically determines the distance it can fly. Battery-based systems are limited to a specific range which may require “range extender” packs for improvements.
Photo: Air Canada
Unlike gas turbine engines which burn fuel throughout the flight, making the overall weight dynamic, the weight of battery packs stays constant, limiting the total range. To extend the range of an electric aircraft, the hybrid system often becomes heavier, more complex, and often inefficient.
Parallel hybrid system
These weight-related challenges in serial hybrid systems often make improving range extremely difficult. As a result, hybrid aircraft manufacturers often settle for parallel hybrid systems. Parallel hybrid systems allow traditional gas turbine engines to provide power (to some extent) in parallel with the electric motor fed by the battery system. According to Airbus,
In a hybrid configuration, the aircraft uses several energy sources in flight, either in tandem or alternately. The combination of energy sources – jet fuel or sustainable aviation fuels with electricity – enables us to optimize overall energy efficiency and reduce fuel consumption.
The parallel power by conventional sources (such as a downsized gas turbine engine) is typically provided during high-power requirements of takeoff and climb. In cruise conditions, the gas turbine generates the power for the fan/propeller. An enlarged embedded starter motor also assists the gas turbine during transient power conditions. While using multiple power technologies may not achieve a zero-emission target, the system substantially improves the range of the aircraft.
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