When a military helicopter and a passenger jet fatally collided over the Potomac River in Washington D.C. earlier this year, the tragedy illustrated a stark truth: Our skies are crowded. And they’re only getting more so. 

When the international trade group for airlines committed in 2021 to “fly net-zero by 2050,” the pledge underlined a growing problem: Aviation already accounts for 3% of global carbon emissions. That’s going to balloon if passenger miles double by 2050, as expected.

When journalists produce a steady stream of headlines about autonomous air taxis, the implication is clear: New electrically powered vertical takeoff and landing (eVTOL) aircraft suggest flying could look wildly different in some corners.

On the front lines of each of those issues — and more — you’ll find Georgia Tech engineers doing the critical research to smooth out the turbulence of a dynamic and changing industry. From designs that move beyond the tube-and-wing flying the skies today to new ways to model passenger demand and offer new kinds of travel packages, Yellow Jacket fingerprints are everywhere.

“Many of these things that are happening [in aviation] have roots directly here,” said aerospace engineer and Regents’ Professor Dimitri Mavris.

So grab a boarding pass, adjust your seat back, and see how engineers are planning, modeling, designing, and building the future of flight.

Windy Cities

If eVTOL vehicles are coming to skies near you, there’s much to do beyond designing the vehicles themselves. A signature research effort looking at the broader picture has been housed at Georgia Tech for more than 40 years.

The Vertical Lift Research Center of Excellence focuses on all areas of vertical lift: traditional helicopters and other rotorcraft, urban air mobility vehicles and drones, and even rotorcraft that could one day help us explore other planets and moons.

Led by Marilyn Smith, the Center operates on a five-year cycle with funding from NASA, the U.S. Army, and the U.S. Navy. Three years into the current cycle, $16 million worth of research is underway on a dozen projects involving 10 faculty members and six universities. The Center also has become a hub for training — one of the few places in the country with a full scope of curriculum for rotorcraft engineers.

It’s potentially life-and-death work if air taxis and drones are to become viable operators.

“Are you designing the vehicle so that it can be the most productive flying through these areas? You don’t want conditions to draw too heavily on the battery so that your battery drains too fast,” Smith said. “If you’re flying a lighter drone, can you actually fly it on that path that day, or is it going to get slammed into the side of a building because it’s just too windy?”

In a related project for NASA — especially timely after this winter’s raging wildfires in California — Smith is modeling the environment around wildfires and fires in urban areas. Her models predict the direction of spread and thermals generated by the intense heat to offer insights on potential impacts and ideal flight paths for drones dropping fire retardants.

Another area of research in Smith’s lab looks at what happens when tilt-rotor aircraft like the RAVEN transition from hover to forward flight. 

“We don’t have good databases for solver validation and to understand the physics for tilt-rotor conversions,” Smith said. “[AE Assistant Professor] Juergen Rauleder is performing extensive experiments on that topic, and we are studying the aerodynamic interactions with him. We’re also making sure we can capture the important physics with the simulation tools we have and develop best practices to capture the physics.”

Smith said the world of advanced air mobility has shifted from feasibility to the just-as-complex questions of operations, which is why her group’s work is crucial.

“People weren’t thinking about this before, because they were focused on so many other things: Can you build vehicles? Are they practical?” she said. “At this point we’re saying, ‘We can build vehicles. They’re practical. Now, how do we operate them safely? What are these other problems that we need to solve?’”

“Traditionally, maybe it didn’t make as much sense to apply game theory here, but now I think it will,” Li said. “We’re losing some of that centralized structure. Imagine you order something from Amazon in the morning — and let’s say advanced air mobility happens. Amazon is going to ship it out in the afternoon. You maybe get a six-hour window to insert that flight trajectory into the current system. We can’t manage air traffic the same way we do now, where we have two years’ lead time to deconflict everything.”

Li sees her work augmenting human controllers trying to process and account for all the constantly updating information available to them. Her models might pull in all that data and suggest optimal routes to avoid conflicts or circumvent developing weather issues. This kind of partnership could mean better overall air traffic handling. 

“Controllers have some idea of what’s going on broadly, but they are mostly focused on local traffic control. Let’s say there are three or four different routing options that they’re more or less OK with locally. Maybe our models could suggest, based on global weather information or global forecasted traffic, you should choose this one if you can,” Li said.

To oversimplify, Li’s models have three main parts. First, they deal with multi-agent systems — in other words, all the individual vehicles using airspace at the same time — and the constraints and objectives for each of those agents/aircraft. Those objectives might be to arrive at their destination on time and use the least amount of fuel.

Second, the model accounts for the system’s dynamics: Behavior and activity change over time, and they happen in sequence. And third, the model incorporates uncertainty: weather forecasts, miscommunications, delays on the ground, and more.

What makes game theory an interesting approach, Li said, is that the objectives of any one flight might be in conflict — or at least affect — other flights. Every “agent” in the system can’t achieve its on-time, fuel-efficient objective without routes that would cause collisions or at least very close calls.

“We want to optimize the objective given constraints,” Li said. “Now these objectives and constraints are coupled to another optimization problem, they’re coupled with respect to each other. That’s game theory.”

She said it’s a valuable approach for thinking about managing the realities of ever-busier skies.

“Game theory is a good framework where now you can look at these multi-agent systems and how their decisions affect each other.” 

Travel packages could include a checked bag, advance seat assignments, or premium lounge access. But they also could include new kinds of nontraditional offerings — maybe free or discounted stopovers to break up long-haul flights. Garrow said the possibilities are vast. And the research need is helping airlines figure those out.

“We’re the math behind the scenes building a better airline experience, offering you products you actually want to buy and lower prices to consumers without steep price jumps you may see right now,” Garrow said. “We’re helping the airline industry stay profitable by finding good ideas and helping them better implement those ideas.”

The lab’s tools can help airlines decide what offers to create for customers, how to price them, and how to promote them to flyers. Their algorithms allow airlines to separate good ideas from bad ones by simulating the impact of those offers or other changes to service.

“Revenue management is such a strong lever. Small changes can have huge impacts on the bottom line or lead to huge losses,” Garrow said. “The value proposition we bring is this ability to model almost the full airline industry — competitive networks, competitive pricing, and revenue management — and allow researchers and industry partners to test out new ideas and quickly evaluate their impact.”

Garrow said her team’s work also helps airlines consider aircraft design questions and anticipate customer needs. They can help decisionmakers figure out when planes need more seats with extra legroom or more premium seats, for instance.

Garrow has long been a go-to resource for the industry. So, when the founder of a research consortium at MIT retired a few years ago, she worked quickly with eight airline and industry partners to establish ATL@GT. Along with research, those connections have also led her to create a graduate-level course on airline revenue management to fill a gap center members identified.

“No two companies are the same, so our role is coming up with a portfolio of the most important research questions that will benefit the industry and consumers.”