Air transport ensures global connectivity, supporting social reach, job creation, and economic growth. To deliver these benefits in a sustainable manner that will also allow aviation to attain its environmental goals will take the combined efforts of all stakeholders, including governments, aircraft and engine manufacturers, airlines, airports, and air navigation service providers.
To date, aviation has exceeded its target of a 1.5% annual fuel efficiency gain. And, looking ahead, the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) will enable the industry to grow without adding to its net carbon footprint.
Even as CORSIA makes its impact felt, evolutionary technologies will continue to deliver an improved environmental performance. Since the beginning of the jet age, lighter materials, better engine performance, and aerodynamic improvements have reduced aircraft fuel consumption per passenger-kilometer over 70%.
And up to 2035, it is expected that other improvements such as natural and hybrid laminar flow control, high-bypass engine architectures, electric landing gear drives, and fuel cells for onboard power generation will all deliver notable efficiency gains. Sustainable aviation fuels, of course, will be another major component in reducing aviation’s carbon footprint.
Electric flying is becoming a reality and we can now foresee a future that is not exclusively dependent on jet fuel
“By applying combinations of evolutionary technologies, fuel efficiency improvements of roughly 25% to 30% compared with today’s aircraft still appear possible,” agrees Thomas Roetger, IATA’s Assistant Director, Aviation Environment. “However, further significant improvements of the classic tube-and-wing configuration powered by turbofans are becoming more and more difficult to envisage after 2035 or so.”
The manufacturers are considering future options, forming partnerships with research establishments and start-up companies and are behind many of the new aircraft design ideas. The strut-braced wing, box-wing, and “double-bubble”—two side-by-side fuselages blended together—are all on the drawing board.
The strut-braced wing allows for a larger wing span, reducing drag and, therefore, the thrust required. This means smaller, more efficient engines. Folding wingtips avoid infrastructure adjustments to accommodate the larger wing span.
The Subsonic Ultra Green Aircraft Research (SUGAR) studies conducted by Boeing and NASA found that a 150-seat strut-braced wing aircraft entering into service by 2040 could be about 30% more fuel-efficient than, for example, today’s Boeing 737-800.
The most hyped design, however, is the blended wing body. Essentially, this is a large flying wing with the passenger cabin or cargo storage area within its center section. The aerodynamic shape generates greater lift, which means the benefits are most obvious in cruise flight.
The blended wing has generally been proposed as an aircraft for several hundred passengers. However, it has recently looked like a realistic possibility to optimize smaller versions of the design for the larger market segment of around 100 passengers. Estimated fuel efficiency gains for larger blended wing aircraft vary between 27% and 50% compared with current aircraft of similar size and range. For the smaller version, the estimate is around 30%.
The real game-changer, though, promises to be electric aircraft. Electric power generation is not emissions-free today, but it can be expected that the related emissions will go down considerably between now and 2050, thanks to the strong worldwide trend toward renewable energies.
In fact, the most optimistic scenario in the International Energy Agency’s World Energy Outlook foresees over 80% of CO2-free electricity after 2040. And an all-electric aircraft would produce no emissions in its operation.
Furthermore, other aspects beyond environmental concerns improve the business case since an electric motor needs less maintenance than conventional gas turbine engines and that is a value that can be put into dollar terms. In short, the numbers are starting to fall on the side of electric aircraft development.
“As a revolutionary technology, electric aircraft are also an opportunity for new entrants,” says Roetger. “And the other positive is that it is a scalable technology. Implementation is already happening step-by-step starting with light, one-seater aircraft before moving into the commercial arena. This not only makes the certification process manageable but will also help the industry gain confidence in this radically new technology. With electric aircraft, there is the chance to prove safety and reliability on a small scale first. Scalability mitigates much of the development risk.”
Wright Electric is working on a design based on distributed propulsion with electric fans integrated in the wings, and on batteries that can be easily exchanged during airport turnaround. The company is working with easyJet on an aircraft that would accommodate 150 passengers and be able to fly up to 540 kilometers covering over 20% of easyJet’s route network. The announced plans suggest an entry into market by 2035.
“The technological advancements in electric flying are truly exciting and it is moving fast,” says Johan Lundgren, easyJet CEO. “Electric flying is becoming a reality and we can now foresee a future that is not exclusively dependent on jet fuel.
“The target range of the electric plane is around 500 km which, within our current route portfolio, would mean a route like Amsterdam to London could become the first ‘electric flyway.’ And as it is currently Europe’s second busiest route, this could in turn offer significant reductions in noise and carbon emissions, with multiple take-offs and landings every day.”
80% - The most optimistic scenario in the International Energy Agency’s World Energy Outlook foresees over 80% of CO2-free electricity after 2040
Hybrid electric aircraft
Battery performance will be critical to electric aircraft, and, at the moment, a battery-powered 100-seat aircraft is still a long way off. Simply put, jet fuel has a high energy density and getting the equivalent ability in batteries makes them too heavy for use.
“Jet fuel has been an ideal energy carrier and the alternatives have issues in terms of weight or volume,” says Roetger.
But, as work on fully electric aircraft continues, hybrid-electric aircraft should be taking to the skies. A hybrid-electric aircraft would use jet fuel as the primary energy source but could then switch to electric motors for propulsion during several phases of flight.
There is a host of hybrid-electric aircraft designs from all the major aerospace manufacturers. These all combine innovative electric motors and combustion engines. An Airbus, Rolls-Royce and Siemens partnership hopes to fly a hybrid-electric demonstrator aircraft, the E-Fan X—based on a BAe 146—in 2020.
NASA, meanwhile, is combining the blended wing design with turbo-electric propulsion—a particular form of hybrid-electric propulsion. The electric blended wing body could provide 70% fuel savings. As smaller aircraft using the blended wing design become possible, the potential for the introduction of such an aircraft increases enormously as it is likely to have a huge market demand, speeding up innovation.
Conservative views predict electric aircraft in the 15-20 seat category will arrive about 2030. Larger aircraft carrying 50-100 passengers would enter into service about 2050. This view suggests more time is needed for battery technology development. Optimistic views take 5-10 years off those estimates, based on interest and public funding of climate change-related technologies. Moreover, a possible alternative to heavy batteries could be hydrogen fuel cells, especially if a worldwide hydrogen supply network becomes a reality in the next 20 years.
“We must encourage the seamless integration of radically new aircraft by making infrastructural adaptations such as high-power electricity supply to airports,” concludes Roetger. “All aviation stakeholders have a vested interest, and all will benefit from their introduction because handling the increasing demand for air travel in a sustainable manner requires these new technologies. The biggest winner of all will be the environment.”
Norway goes electric
Some proactive governments are joining aviation’s call for environmentally-friendly aircraft. By 2040, Norway hopes all short-haul flights leaving its airports will use electric aircraft.
Norway wants the first 25-to-30-seat aircraft powered by electric motors to be introduced into service as early as 2025. The country is ideally suited to be a pioneer in the field given its reliance on short-haul flights to remote communities, especially when winter blocks roads and rail tracks.
“A lot of the flights here are only 15 to 30 minutes,” says Dag Falk-Petersen, CEO of the country’s airport company, Avinor.
The argument is that most of the aircraft flying short-haul routes today are really designed to fly longer routes. That means they are larger and heavier than necessary. So, for much shorter routes, a smaller aircraft will be much easier to power with electricity. Smaller aircraft means smaller airports and runways. And they will be much quieter too.
Potentially, they will be cheaper to operate as well, making it possible for airlines to continue the trend in offering lower fares in real terms.
2040 - The Subsonic Ultra Green Aircraft Research (SUGAR) studies conducted by Boeing and NASA found that a 150-seat strut-braced wing aircraft entering into service by 2040 could be about 30% more fuel-efficient than, for example, today’s Boeing 737-800.
Engines roaring on
Engines are the key component in the industry’s incremental improvements in fuel efficiency. Most new engines have higher bypass ratios (BPRs) than older models. Basically, the higher the BPR, the greater the improvement in fuel efficiency.
Rolls-Royce is working on two new designs planned for launch in 2020 and 2025. The Advance engine is expected to achieve at least a 20% reduction in fuel burn and CO2 emissions relative to the Trent 800 and the Ultrafan engine will develop that to an expected minimum 25% improvement in fuel burn and CO2 emissions relative to the Trent 800.
Safran is also working on Ultra-High-Bypass Ratio (UHBR) turbofan engines and other manufacturers have similar innovative designs. In addition, Safran is looking at open-rotor technology. The open rotor—which uses two counter-rotating, unshrouded fans and is a combination of propeller and turbofan technology—is actually an old design but was not pursued as it was too noisy. But work on reducing the noise has made open rotor viable with an expected entry into service around 2030. A reduction of fuel burn and CO2 emissions of about 30% compared with conventional turbofan engines is possible.