Replacing combustion engines with electric motors is fundamentally changing the ways land vehicles are propelled, fueled and lubricated. Until recently, aerospace had dodged the legislative and consumer pressures for a switch to a low- or even zero-emissions aviation industry.
Fixed- and rotor-wing electric aircraft are on their way to commercial takeoff within a decade, as electrification gradually gains momentum in the aviation industry. Aerospace engineers are developing hybrid and full-electric planes and helicopters to improve fuel efficiency, mitigate carbon dioxide emissions and take advantage of novel opportunities in urban mobility.
Aerospace design is influenced by inherently more conservative dynamics that favor incremental changes to engines and airframes. Unlike cars, which outnumber airplanes by several orders of magnitude and are essentially off-the-shelf products stocked in showrooms, most aircraft are made to order at a significantly higher price. They also have longer service lives, translating into a relatively slow replacement rate.
Crucially, an extensive history of safety regulation, reliability improvements and airworthiness certification costs (excluding CO2 emissions) continue to discourage aircraft original equipment manufacturers from taking innovation risks such as electrification. The variety of aircraft architectures, applications and power requirements complicate regulation and CO2 mitigation, too.
The past few decades of gradually increasing fuel prices – albeit with the occasional spike and crash – have squeezed margins and pushed commercial aircraft OEMs to make efficiency improvements to airframes and engines. At the same time, operators have reduced fuel consumption by replacing older aircraft with newer, more fuel-efficient models, changing routes and fitting turbulence detection systems, for example. Higher occupancy rates and load factors have also contributed to better fuel efficiency.
From 2000 to 2016, overall commercial aviation fuel efficiency improved by 2.9% (international aviation was 2.2%), according to the International Energy Agency. Emissions of CO2 per revenue ton-kilometer for global flights improved by more than 12% from 2010 to 2018, according to the International Air Transport Association.
This gives a false picture of reducing emissions, which after all is the raison d’être for vehicle electrification. From 2013 to 2018, global commercial aviation’s CO2 emissions rose 32% as overall fuel consumption soared on updrafts of increased passenger and cargo traffic, according to the Airports Council International.
Moreover, consulting company Roland Berger predicts a rise in emissions from aviation based on projections of continued growth of passenger travel and diminishing returns on further modifications of engine technology and airframe architectures.
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Aerospace engineers are developing hybrid and full-electric planes and helicopters to improve fuel efficiency, mitigate carbon dioxide emissions and take advantage of novel opportunities in urban mobility.
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As yet, there is no international legal framework surrounding aircraft emissions, but it is on the cards. The International Civil Aviation Organization, a specialized agency of the United Nations, set energy efficiency goals and policies for international aviation. The ICAO’s policies intend to reduce CO2 by limiting emissions from new aircraft, a resolution targeting 2% annual efficiency improvement by 2050 and a means to maintain CO2 emissions at the 2020 level through the Carbon Offsetting and Reduction Scheme for International Aviation. The scheme entails reporting CO2 emissions for international flights on an annual basis.
In January 2019, 79 countries responsible for 77% of passenger-kilometers voluntarily agreed to participate in these ICAO policies. If the organization’s offsetting scheme is implemented fully in the future, operators of airlines that exceed limits would compensate by “paying for the privilege” and underwriting green activities.
Regardless of the regulatory shortfall, the commercial aviation industry is moving in the right direction on its own by using sustainable and synthetic aviation fuels, retrofitting aircraft with energy-saving equipment, improving air traffic management and routing and developing new technologies for airframes and propulsion systems.
The IEA claims that completely new “clean-sheet” or “start-from-scratch” aircraft designs offer the largest potential efficiency gains, although this approach entails significant investment and lead times before commercialization.
According to a report by the International Air Transport Association, next-generation commercial aircraft (produced until 2035) will continue to be evolutionary modifications of existing tube-and-wing airframes with turbofan jet engines that burn conventional aviation fuel or sustainable drop-in equivalents. These modifications could include retrofitting conventional aircraft with active laminar flow equipment, riblets, adaptive trailing edges and geared turbofan engines.
As far as even partial electrification goes, fuel consumption could also be considerably reduced by technologies such using e-motors mounted in the main landing gear for taxiing instead of the main engines or a towing tractor. The IATA also forecasts novel airframes such as blended wing bodies and strut-braced wings, and propulsion systems including open rotors, boundary layer ingestion and hybrid and battery e-motors.
The power output to weight ratio of present-day e-motors and lithium-ion batteries similar to those in land vehicles is insufficient for the primary propulsion of commercial aircraft. However, they could be a useful supplement to combustion engines in hybrid aircraft propulsion by providing additional energy for peak load operation, such as takeoffs.
As in the automotive arena, all-electric aircraft propulsion systems use batteries, while hybrids use gas turbines for primary propulsion and charging batteries to power e-motors for secondary propulsion during specific phases of flight, as well as drive generators and power inverters. According to the IATA, there are a number of electrically powered general aviation (smaller private) aircraft are already in use and by mid-2018, there were about 100 e-aircraft projects in development worldwide, up from 84 in 2017 and 44 in 2016 (including prior years). Most of these are based in Europe and the United States with the rest in China, Israel and Brazil. Most focus on smaller general aviation architectures.
Current aerospace electrification technologies are better suited to less power-hungry aircraft. While e-motors of the appropriate size and power for commercial aircraft are available, current lithium-ion battery technology is only feasible for smaller planes. All-electric general aviation aircraft are closer to commercialization than larger commercial hybrids.
The e-aircraft sector is heading toward commercialization of 15- to 20-seat aircraft by 2030 and larger 50- to 100-seat regional planes by 2035. Based on predictions of future passenger numbers and other air transport developments, the IATA projects the introduction of e-aircraft with more than 150 seats before 2050 and that the industry can achieve a 25% reduction of CO2 emissions. In addition to fuel efficiency and emissions benefits, the IATA predicts aviation e-motors will provide additional advantages over ICEs, such as lower maintenance costs, better air quality and less noise. However, the need for high-power electricity supplies to recharge batteries will present a challenge.
The IATA considers hybrid electric aircraft to be “a very effective substitute for conventional short- and medium-range aircraft in the near future.” Aircraft OEMs, electric equipment providers and specialized companies are currently developing a variety of electric technologies to propel aircraft and supply energy onboard.
In Europe, Airbus, Rolls-Royce and Siemens formed a partnership in 2017 to develop a hybrid demonstrator aircraft, and in 2019 Scandinavian Airlines and Airbus are cooperating on research relevant to commercialization of hybrid and e-aircraft. In the U.S., NASA is working on an experimental turboelectric aircraft, while start-up Wright Electric and partner easyJet are developing a battery-powered aircraft for short-haul transport of 150 passengers over distance up to or 537 kilometers (290 nautical miles) by 2035.
Electrification could initiate a boom in regional commercial air travel. Cars, trains and buses are still cost-competitive and convenient, while flying can be expensive. Airports are also often far from urban centers because of noise and air quality. All-electric regional commercial aircraft would mitigate these problems and may lead to the construction of electric-only airports near or even in cities.
For India and China, for example, infrastructure for convenient regional commercial aviation might tip the balance away from intercity land travel. Electrified regional commercial aviation could also take off in parts of the world where many flights are shorter than 45 minutes, terrain is inconvenient for land travel and petroleum-based fuels are not readily available.
China, in particular, may become a leading global player in e-aviation by virtue of its command economy that has shaped the global electronics, solar power and EVs industries already. With no major domestic airframe or aircraft engine OEMs, China is positioned to move ahead to commercialize e-aircraft without risk to a legacy aviation industry.
E-motor and battery technologies have opened the door to the development of a new aviation segment – urban air mobility, comprising intracity transportation systems for faster and more efficient movement of people and goods through the skies above congested cities.
To generate lift, fixed-wing aircraft need wings and forward thrust, typically produced by burning energy-rich fuels. They also need a runway. Helicopters use bladed rotors to generate lift without forward motion, allowing them to take off and land in a relatively small space. They can also access terrain off limits to fixed-wing aircraft.
With conventional helicopters come the downsides of cost, vibration, noise, emissions and instability, which have limited their use as air taxis in urban settings.
Companies such as Bell, Sikorsky, Honeywell, Toyota, Airbus, Ehang and Uber are developing e-helicopters for use as air taxies and autonomous delivery craft in a “third dimension” of urban transportation. They are promoting electric vertical takeoff and landing aircraft as a feasible alternative for urban air mobility in mega-cities. Investors have jumped onboard to support e-VTOL projects despite concerns of helicopter safety.
The e-VTOL market will grow to $411 million from $162 million between 2025 and 2030, driven demand for increase operational efficiency and reduce human intervention for intra- and inter-city transportation, according to analysts Markets and Markets.
This growth is being driven by companies such as German start-up Volocopter GmbH. The company produces two e-VTOLs: the Volocopter 2X, a personal air vehicle, certified as airworthy for use as an air taxi in urban areas, with capacity for pilot and passenger, total load of 160 kilograms, range of 27 kilometers at 70 km per hour; and the two-passenger VoloCity, with a 200 kg payload, 35 km range and a maximum speed of 110 km/h generated by 18 battery packs powering nine rotors.
Aviation lubricants comprise a modest but expanding segment that will grow to $1.4 billion by the end of 2027 from $910 million in 2019, driven by increasing demand for passenger and cargo transport, according to Transparent Market Research.
Commercial jet aircraft account for the single-largest segment of aviation lubricant demand, followed by piston-engine aircraft, helicopters, military aircraft and other business jets and turboprops. Roughly two-thirds of volume is engine oils, followed by hydraulic fluids, greases and miscellaneous products.
The effects of aviation electrification on the lubricant industry will depend upon wide range of factors influencing adoption electrified aircraft. Foremost is the willingness of governments to accept and implement limits on aviation CO2 emissions. This is closely followed by commercial-scale development of aviation e-motors, generators, lithium-ion batteries and other e-aircraft technologies including lubricants optimized for e-motors, generators and components.
Conventional aircraft technology still has the sticking power to compete with e-aircraft in the race to reduce CO2 emissions – novel airframe designs, innovative engine, operational improvements and hydrocarbon fuel taxes, among others.
Other obstacles could be the development of new airworthiness criteria, evaluations and certification standards for electrified aircraft; development of airport facilities, such as charging stations, and urban air mobility infrastructure with acceptable safety, security, noise levels, air quality and cost for travelers.
Lastly, e-aircraft have to gain by consumer trust, which relies heavily on demonstrated safety, reliability, convenience and comfort.
It appears likely that there will be at least a partial shift in demand for conventional aircraft lubricants to new products optimized for e-aircraft. This gradual transition will take place over the long term, along with fleet replacement and putting into service urban air taxis and eVTOLs.
Historic standards and expectations for reliable, safe, economical operation of conventional aircraft will apply to e-aircraft too, as well as regulation of CO2 emissions. There may also be tension between increasingly sophisticated technical performance requirements for aviation lubricants used in sealed-for-life e-motor components, as is the case for automotive EVs.
The lubricant industry needs to anticipate how it will adapt to inevitable changes in aviation, as it must with automotive developments. Nevertheless, the long-term outlook for increasing passenger and cargo air transport worldwide bodes well for the future of aviation lubricants.
