As mobility’s industry revolution on the ground captures all the press—electric and fuel-cell vehicles, driverless cars, etc.—it should not be a surprise that the aerospace industry’s drawing boards are full of exciting new designs. Beyond advances in technology, key drivers behind the new designs are some significant increases expected by the aircraft industry 2050: A seven-fold increase in air traffic and a three-to-four-fold increase in carbon dioxide (CO2) emissions. This compares with only a doubling of the world’s ground vehicle fleet in the same timeframe.
Aircraft emissions is one of the main reasons that the transport sector is expected to be a key player in the climate change challenge ahead. A report by the International Council on Clean Transportation (ICCT) suggests that if counted as a country, globally the aviation sector would rank 7th in terms of CO2 emissions, just after Germany and well above Korea in 2011. The sector stands to cancel out the gains made in emissions in other sectors as the disparity continues to grow in the decades ahead.
Unlike ground vehicles, for which each country has developed its own emissions standards, aerospace fortunately has an entity that is working on a global solution: the International Civil Aviation Authority (ICAO), a UN body that writes the high-level standards all countries must comply with. It has been behind the drive to reduce aircraft noise (1972) and implement standards for air pollutants (1981). Now it is working to develop a common set of CO2 and particulate matter (PM) standards for all manufacturers worldwide.
SAE International enjoys a strong relationship with ICAO, underpinning its emissions regulations with the necessary technical standards for measurement and modelling. SAE has also been tasked by ICAO to develop a performance-based safety standard for the air shipment of lithium batteries.
Dramatic increases in fuel efficiency will be needed for future commercial aircraft—not only to continue to manage the cost of air travel, but also to deal with the emissions challenges. Many aerospace researchers argue that the design of future airliners needs to change, as the current “tube and wing” architecture is outdated. With the advances in aerodynamics and in computer-aided tools, that design has been refined and perfected for decades to a point where it has reached its asymptotic limits of efficiency.
But nature is still way ahead of us. Studying how birds “morph” their shapes—and even surfaces—as they fly, aircraft designers are learning that aircraft could be significantly more efficient if they could develop flexible structures. While the old model is efficient during steady flight, fuel efficiency drops during transitional conditions. If aircraft could change their wingspans or their shape during flight, fuel efficiency—and in turn CO2 emissions—could be improved by some 20%, designers believe. This research is what led Mike Griffin, President of AIAA, to state at SciTech 2014, “Biology is becoming the new basis for technology.”
Beyond design architecture, the other key variable is the propulsion system. There are two options: low-carbon biofuels and electrification.
Biofuels offer some 40-80% improvement over carbon fuels in emissions. There is considerable experimentation under way, with virtually every major airline having advertised test flights with biofuel power. A joint program sponsored by leading European airlines (Lufthansa, Air France/KLM, and British Airways) and key European biofuel producers (Neste Oil, Biomass Technology Group, and UOP) is called the European Advanced Biofuels Flight Path. It is a roadmap for producing 2 million tons of sustainably produced biofuel for aviation by 2020. But the road is a difficult one, as there are a number of hurdles—including a lack of both biofuels policies worldwide and long-term agreements between biofuels producers and the aviation industry to support investments. And, there is the price issue; biofuels are still too expensive, and many believe it will be a decade before parity with carbon fuels can be achieved.
The other path to cleaner propulsion is electrification, as it stands to deliver zero CO2 and NOx emissions. This, of course, is assuming the electricity can be sourced from clean power. The advances in lithium–ion (Li-ion) batteries for consumer electronics, and more recently for electric vehicles, are already expanding supply and driving costs down. Large-form-factor Li-ion battery cell costs that are used for electric vehicles have already come down some six- to seven-fold since the first mass-market EVs like the Nissan Leaf and the Chevy Volt hit the market early this decade. At the same time, battery power density is increasing rapidly. Tesla CEO Elon Musk is on record saying that once batteries are capable of producing 400 watt-hours per kilogram, with a ratio of power cell to overall mass of between 0.7-0.8, an electrical transcontinental aircraft becomes “compelling.” If we look at the forecasts from key EV suppliers like LG Chem, those parameters are likely to be within reach by the early 2020s. And SAE International’s Electric Aircraft Steering Group is currently laying out the landscape for the standards needed to support more-electric aircraft including hybrid-electric and all-electric propulsion systems.
Interestingly, the FAA estimates that there are already some 500,000 electric aircraft of a certain type flying the skies of the United States: drones. Many are battery powered, as any electric aircraft would be today, but advances in solar power stand to further contribute to the future of electric aircraft. Although solar cells can only still claim conversion efficiencies about 20%, their costs have come down exponentially in the last decade and are continuing to fall. The historic flight of the Solar Impulse, the first solar plane to circumnavigate the globe with no fuel in 2016, has put the concept of solar-powered electric aircraft on the map of the possible.
SAE international enjoys a stellar reputation in the aerospace sector among regulators such as ICAO, FAA, and EASA to OEMs and suppliers. In fact, the aerospace business of SAE is expanding rapidly, in particular supporting the safe introduction of new and exciting technologies.
What a great time to be an SAE aerospace engineer.