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In 1883, the airship La France made history as one of the earliest recorded examples of electric propulsion in aviation. Powered by a 435 kg zinc-chlorine flow battery, the airship completed a full 8km round trip. Once the Wright brothers completed the first heavier than air flight using gasoline, however, electric aviation became a niche pursuit in an industry that exploded in innovation around the internal combustion engine, particularly after the dawn of the jet age.
More recently, however, the advancement of full battery-electric, hybrid and hydrogen fuel cell-electric planes, UAV’s and rotorcraft, has become a significant focus of the aviation industry to improve the sustainability and economics of modern air travel. It has been widely suggested that electric engines for propulsion can deliver cleaner and quieter flight, reduced dependency on fossil fuels and enhanced operational efficiency and cost savings.
Electric aviation offers enormous potential for increased connectivity for people all over the world and the opportunity is being seized by innovators developing exciting new aircraft and electric propulsion technologies to unlock new advanced air mobility and regional connections. Whilst many electric aircraft applications will be limited by range capability in the short-term, as propulsion technologies are refined, innovators are targeting scaling up to narrowbody aircraft for commercial air transport.
In this blog post, we outline the benefits and applications of electric aircraft, developments in electric motor technology and what the near-term future could look like for the regional aviation and developing urban air mobility markets.
Conventional ICE aircraft use no electric power or electrical energy for their propulsion and instead use the internal combustion of liquid fuels for mechanical propulsion. Electric aircraft can be categorised into differing groups according to the degree of hybridisation of their electric motor power and energy source (i.e., battery or hydrogen).
Full-electric or battery-electric aircraft exclusively use electrical energy and power for propulsion. Energy is stored in a battery onboard an aircraft.
Hybrid-electric aircraft use a combination of fossil fuel or SAF and electrical energy storage, usually with a gas-turbine alongside an electric motor.
Hydrogen-electric aircraft use hydrogen fuel cells to generate electricity (from stored gaseous or liquid hydrogen fuel) with an electric motor for propulsion.
Specific energy (energy per unit mass of energy storage), specific power (power of a component per unit mass) and also volumetric energy density (the amount of energy stored in a given volume) determine the available range and payload for the electric aircraft. In practice, that means innovators must consider these when selecting what form of electrification they are seeking to integrate to support what type of flights.
Applications include:
Battery-electric aircraft are currently limited by the energy density of existing battery technologies, meaning the range will be insufficient for large commercial aircraft. However, the environmental benefits and increased efficiency and economics of the system provides a suitable alternative for fixed-wing short commuter flights, UAVs and new urban air mobility applications like eVTOL taxis.
Hybrid and hydrogen-electric aircraft are predicted to capture routes of longer ranges in the fixed wing sub-regional segment, as well as rotorcraft, UAV and novel clean-sheet applications. Whilst hydrogen has 100 times the gravimetric energy density of lithium-ion batteries, it is currently limited by the low volumetric density of hydrogen fuel. Yet as electric motor and hydrogen storage technologies improve, hydrogen-electric has potential to scale for commercial aircraft applications, providing truly clean electrified flight.
Traditional electric motors for aviation are hindered by weight and heat generation inefficiencies. The latest permanent magnet synchronous electric motor (PMSM) technologies deployed in automotive and other sectors are being pushed even further to deliver aerospace level capability. PMSMs offer numerous advantages, as they deliver greater efficiency and heat transfer, higher specific power and speed, reduced noise, greater compactness and increased life spans. Permanent Magnet electric motors work through the interaction of magnetic fields, one created by the permanent magnet in the rotor and the other generated by the current flowing through the stator windings. The interplay between the two magnetic fields creates a force that causes the rotor to turn, and this mechanical energy ultimately turns the aircraft propellor(s). Having a permanent magnet present reduces the overall amount of electricity needed for magnetic field generation, leading to reduced energy loss.
Developments using superconducting material or high purity metals are other avenues that may allow increases in specific power – super conducting materials exhibit zero electrical resistance below a critical temperature. When superconducting materials are used in the rotor or stator components, they have virtually no electrical resistance to steady current, meaning they can carry up to 100x more current density that copper conductors at room temperature. Whilst the challenge of increased cooling apparatus and weight must be considered during cryogenic operation, cooling using cryogenic fuel like liquid hydrogen may offer a solution in the future.
In addition to technological advancements, many steps are being taken to gain a better understanding of the certification standards that will be needed. ZeroAvia recently announced that it’s 600kW electric propulsion system has received a G-1 issue paper from the US Federal Aviation Administration, defining the basis of its certification for aerospace. This already highlights the maturity of the design and applicability to aerospace applications.
Electric aircraft propulsion can enable new urban mobility and regional aviation sectors. A report by the World Economic Forum and McKinsey suggests that by 2050, up to 38% of the global fleet could be replaced by alternative propulsion (including battery, hydrogen-electric and hydrogen combustion). With an estimated 79,000 fixed-wing aircraft (in storage/service) globally within the <950kW power range, based on recent Cirium data, there is a huge opportunity for clean aviation innovators to capture the existing short-commuter and regional market and drive the creation of new low-cost routes and regional hubs for enhanced connectivity.
In America, it’s calculated that there are 5,050 underutilised airports and only 1.6% of all trips between 50 and 500 miles are taken by air. Many of these are positioned on acres of public land, which could be used for renewable energy generation from solar or on-site hydrogen production and storage.
As well as this, by 2040 it’s predicted that there could be already be 12,000 eVTOL deliveries, rising to 33,000 by 2050. Existing eVTOL designs are already maturing through certification and are expected to enter into the commercial market in the next few years.
It’s clear that electric aviation will bring many advantages for a new era of flight, yet advancements in several areas will be necessary for their widespread commercial adoption. These include: infrastructure development i.e., battery charging, hydrogen production or grid integration; policy and regulatory advancements and technological developments in energy and fuel storage and electric motor technology. At ZeroAvia, we are joining this challenge by delivering breakthrough innovations in electric propulsion technology, to help take a generation of new electric aircraft designs off the drawing board and into the air.