Electric and hybrid aircraft, hydrogen power, advanced airframes and more were on the table at the University of Michigan’s first symposium on sustainable aviation.
The goal was two-fold. First, the Michigan Initiative for Sustainable Aviation sought to gather people from all sides of the industry in a room together to discuss potential solutions to aviation’s emissions problem—and what it would take to make them operational. And second, they wanted to learn how the university could best support the shift to sustainable aviation, filling gaps in the research landscape and training students with the right skills to guide the transformation of an industry.
“There has hardly been a more exciting time to be an aerospace engineer,” said Gökçin Çinar, an assistant professor of aerospace engineering at U-M, who led the organization of the event. “As the need for sustainable aviation intensifies, we have an opportunity for more rapid change than the industry has seen since the invention of the jet engine.”
Indeed, the symposium was full of ideas, including efforts from aviation’s giants such as Airbus, Boeing and Pratt & Whitney as well as from startups developing small planes and innovating in energy generation and distribution.
“I think this is an amazing initiative that the University of Michigan is taking on. You could be a pathfinder for the United States, bringing stakeholders to the table to figure out how to do this,” said Gaudy Bezos O’Connor, project manager for the electrified powertrain flight demonstration program at NASA Langley.
And the Michigan Initiative for Sustainable Aviation intends to lead, as the team now aims to launch a large-scale collaboration to tackle challenges raised at the symposium, in partnership with technology developers, aviation operators and government agencies.
Biofuels remain the most immediately accessible tactic for reducing the climate impact of existing aircraft, but they may require too much land to offer a complete solution. In his presentation, Mirko Gamba, an associate professor of aerospace engineering, showed that biofuels based on soy require a land area the size of Alaska, California and Texas combined to provide all of the fuel that U.S. aviation requires.
Biofuels made from algae, on the other hand, could produce the same amount of fuel with an area the size of New Hampshire. However, land-efficient algae biofuels have yet to be integrated into real-world fuel production, whereas soy is already the key ingredient in biodiesel. Biofuels from food crops are already being demonstrated by airlines.
Electrification is perhaps the heaviest zero-emissions solution, with current batteries capping out around 300 watt-hours per kilogram. Bezos O’Connor raised the goal of 1000 watt-hours per kilogram, which was the topic of another recent electric aviation event at U-M.
Meanwhile, Matt Hutchison, vice president and chief engineer of Boeing’s vertical lift division, pointed out that kerosene has an energy density of 6000 watt-hours per kilogram, running in engines that are 50% efficient.
“That’s hard to beat,” he said.
The weight penalty means that batteries take up space that conventionally has been used for seats and cargo, and they can’t yet power large planes. Still, startups are beginning to launch electric and hybrid airplanes for 10 passengers or so.
Electra.aero is focusing on the air taxi and regional markets. Its design can use runways about the length of a football field—1/10th the runway required for even small airports—to ferry passengers from airports to city centers. AMPAIRE, on the other hand, is exploring hybrid powertrains in which electric and conventional propulsion are used in parallel or integrated together. And there are many more electric aircraft companies out there, some focusing on air taxis that take off and land vertically, as well as efforts at Boeing and Airbus.
Susan Ying, the senior vice president of global operations at AMPAIRE, says that with the integrated hybrid powertrain, “We’re able to save up to 70% of energy and emissions.”
However, certification is particularly challenging. “Have you heard about certifying 1.5 engines on an airplane?” she asked, to laughter from the room.
Like electricity, hydrogen suffers from being a relatively diffuse source of energy in gas form and from being needy in liquid form. Hydrogen liquifies at -253°C (-423°F)—or 20 Celsius degrees above absolute zero, the coldest temperature known to physics.
Yet the need for extremely cold temperatures could come with a silver lining, said Amanda Simpson, vice president for research and technology at Airbus Americas. If cryogenic equipment is already on the plane, it may be feasible to reduce some electrical losses with superconducting circuits. Superconductors can transmit electrical current without the losses to resistance that heat up our phones and computers, but so far, the only known superconductors need to be cooled well below Antarctica’s winter lows.
Universal Hydrogen is developing modular hydrogen fuel capsules that can be used to power fuel cells or burned in a hydrogen jet engine. It intends to demonstrate regional turboprop aircraft that have been converted to fly with electric propellers powered by fuel cells in the 2020s, followed by single aisle aircraft that burn hydrogen in turbines in the 2030s.
“Why are gas stations called Exxon, Shell, Mobile?” John-Paul Clarke, co-founder and chief innovation officer at Universal Hydrogen, asked. “Because they had to build out their whole distribution system.”
The hydrogen industry may have to do this too. Along the same lines, Simpson suggested that the move to hydrogen might expand what airports do: “You can make airports, which today are transportation hubs, into the energy hubs of the future.”
She reported that Airbus is in discussion with Delta about what size hydrogen-powered aircraft would be right for them, as they intend to begin producing zero-emissions aircraft by 2035.
Beyond the logistics of hydrogen fuel, how to make it truly clean and cost effective is an outstanding challenge. Most industrial hydrogen comes from methane, a method that is about 65% to 75% less energy intensive than producing clean hydrogen from water. The University of Michigan has a cohort of researchers exploring the possibilities of the hydrogen economy, including how to produce it without relying on natural gas.
Different designs can improve the efficiency of aircraft. For instance, longer wings can reduce the fuel burned over the course of a flight. Although the extra weight comes with a penalty during takeoff, it’s more than made up during cruise, said Joaquim Martins, the Pauline M. Sherman Collegiate Professor and a professor of aerospace engineering at U-M, in his discussion of aircraft design optimization. Boeing is making long wings lighter with a truss braced design, which it will demonstrate with support from NASA.
However, we may be heading for a departure from the familiar tube and wing in the coming decades. Blended wing body designs can reduce fuel burn by 30 to 40% for the same wingspan. With wide bodies that taper into the wings, the entire surface produces lift.
This design is key to JetZero’s plans. While clean hydrogen and electric power are both more expensive than jet fuel per unit of thrust, reducing energy needs can bring the cost of sustainable passenger journeys back down.
In addition, JetZero’s design doesn’t require many of the moving parts needed to steer conventional aircraft—no flaps or slats, no tail rudder. This makes maintenance simpler, and simulations show that its noise footprint should be just 20% the size of a Boeing 737-800, Vassberg reported.
What it takes to get there, and a university’s role
In her talk, Bezos O’Connor gave an overview of the major challenges that still face both electrification and hydrogen. How will they prevent high voltage arcing at high altitudes? When the air is thinner, it’s not as effective at providing insulation between neighboring electric components.
And for every million watts of power, she noted, there will be 200 thousand watts of waste heat.
“Electric motors generate a lot of thermal energy,” said Rickey Shyne, director of research and engineering at NASA Glenn. “Do we dump it or capture it in a regenerative cycle and use it for something else onboard?”
As for hydrogen, its problems include energy density and storage, plumbing and sealing, material compatibility so that parts don’t degrade, and crashworthiness.
“We did this for the shuttle,” Bezos O’Connor said. “We have a lot of solutions on the space side of the house.”
However, she noted that the sustained presence at high altitude presents some different challenges than a trip from the ground into space.
These hurdles and more face the sustainable aviation movement, but those at the symposium were optimistic about what can be achieved in the next few years and into the 2030s.
Bezos O’Connor challenged the entrepreneurs to think in terms of FAA regulations as they try to gain the support of state and local governments, airlines and airport authorities, which abide by them every day. These regulations were already top of mind for many speakers and panelists—particularly the regulations governing the engines. As Ying pointed out, these need to be updated to account for new methods of propulsion. Certification was high on the list of ways that the group in the electrification break-out session thought that universities could help advance sustainable aviation.
As seen previously with the initial certification of the Boeing 737 Max 8, it is critically important for FAA regulators to fully understand new technologies. This could turn out to be an important role for university researchers, who are deep enough in the state of the art to ask the right questions about safety and reliability.
Perhaps the obvious way for university researchers to help drive sustainable aviation is to help fill in the knowledge gaps, particularly for technologies that are low on the nine-point “technology readiness level” scale. Irewole (Wally) Orisamolu, associate director of advanced concepts and technology at Pratt & Whitney, reported lively conversations with faculty and students about approaches that are interesting to industry but not yet sure enough to make a bet on.
Fundamental research into materials and their applications was another theme among the speakers. Lighter and stronger materials could change the game in airframes and hydrogen storage. New chemistries could enable batteries with higher energy densities. Materials with multiple functions could improve both weight and space efficiency.
“If we’re going to invest in something that’s going to be game changing for what we want to do, it’s advanced materials,” said Shyne.
The other obvious role for universities is in turning out more engineers, but with a twist: participants discussed the need for a slightly different kind of aerospace engineer.
“We talked about how to develop engineers who think on a broad ecosystem level rather than specific technologies,” said Simpson.
All engineers should have some training in how to take that broad view, she said, but there is also an emerging need for engineers who specialize in understanding the entire industry as a system. One tactic the group suggested is an aviation ecosystem course that brings in representatives from industry and government to discuss large-scale challenges that may feel distant to an engineer designing an individual part.
The symposium offered a venue to exchange ideas from nearly every angle of the industry, including those not just making aircraft or researching technological problems, but also those operating them.
“Our goal is to launch a collaborative platform to address pressing challenges and opportunities,” said Carlos Cesnik, the Richard A. Auhll Department Chair of Aerospace Engineering. “What are the most critical issues? Which of these most benefit from a collaborative research approach?”
The participants found common ground in the break-out discussions, exploring angles on sustainable aviation topics that they might not normally consider in their day-to-day work.
“At the end of the day, these new aircraft technology must be operated efficiently by airlines, and within a larger ecosystem such as at the airports. Consideration must be given to the harmonization and operational aspects, as well as the impact on infrastructure. This is only achievable through conversations and collaborations among a diverse set of collaborators,” adds Max Li, an assistant professor of aerospace, industrial and operations, and civil engineering at U-M.
The Michigan Initiative for Sustainable Aviation took care to bring in representatives from airlines and airport operations to ensure these conversations take place. At the same time, folks on the operations side could benefit from a closer view of the technology in development.
“Having different backgrounds brought out ideas that wouldn’t have been raised if we were all from the same part of the industry. The diversity of thought made our discussions more fruitful,” said Tim Niznik, director of analytics at American Airlines.
However, he said, very little can happen without policy to incentivize the change. Publicly traded companies like the major airlines can’t make expensive changes without a solid business case. Here, too, Michigan Initiative for Sustainable Aviation has the potential to play a role, collaborating with U-M’s Ford School of Public Policy.
“For us at Michigan, the event served as a catalyst, enabling a deeper understanding of the industry and government’s urgent needs, and bringing to light the critical barriers that we at U-M are ready to tackle,” said Çinar.
“It also enabled us to strengthen our ties with partners in industry and government as we prepare to establish a premier research and education center for sustainable aviation in Michigan. This center will leverage the robust sustainability ecosystem at U-M as well as ideas and resources from our partners as we find collaborative solutions to challenges facing sustainable aviation.”