Over the next three years, Embry-Riddle Aeronautical University will send cohorts of students to Brazil to study one of the most pressing challenges facing electric aircraft: thermal management.
The university on Friday announced a collaboration with Brazil’s Instituto Tecnológico de Aeronáutica (ITA) that will send students on 8- to 10-week trips in pursuit of strategies to keep electric aircraft batteries cool.
The research is backed by a $450,000 National Science Foundation grant. It will be led by Embry-Riddle engineers Drs. Sandra Boetcher and Mark Ricklick and their counterparts at ITA.
“Both sides have been working on the heat management challenge, so there are some real synergies,” Boetcher said in a statement.
Like the U.S., Brazil has a large aerospace manufacturing industry, most notably regional jet manufacturer Embraer and its electric air taxi unit Eve Air Mobility. According to the announcement, ITA is “affiliated” with Embraer.
The Electric Aircraft Predicament
In an electric aircraft, a single overheated battery cell could trigger a chain reaction that causes the battery pack to catch fire or explode. Developers of electric aircraft must take pains to ensure that the batteries are sufficiently cool not only on the ground but for the duration of flight.
Overheated cells can also translate to permanently degraded performance, battery life, and charging efficiency. Electric models generate large heat spikes during takeoff and landing, the most energy-intensive phase of flight. Their power demand can vary widely across phases, adding to the complexity of thermal management.
One method of thermal management involves the use of outside air to cool the batteries. But that can create what Matthew Clarke, assistant professor of aerospace engineering at the University of Illinois Urbana-Champaign, described to Aerospace America as “cooling drag.” Clarke leads the university’s Laboratory for Electric Aircraft Design and Sustainability, which studies battery thermal management and other topics.
In short, the air that exits the plane moves slower than the air flowing over its wings, causing a pressure differential that creates turbulence and drag. By Clarke’s estimate, relying solely on outside air for cooling can reduce total thrust by up to 15 percent.
To avoid those pitfalls, many electric aircraft developers are combining outside airflows with liquid coolant. Pipistrel’s Velis Electro, for example, has air intake valves that work in tandem with an inflight liquid coolant system to reduce cooling drag. The Velis is designed to fly for about 50 minutes and land with 45 minutes of battery reserves.
Joby Aviation told Aerospace America that its electric vertical takeoff and landing (eVTOL) air taxi—designed for shorter, 10-15 minute trips—is equipped with “active cooling plates mounted between each battery’s individual cells, which maximize coolant flow over the cells.” Its charging stations also have built-in thermal management systems.
Beta Technologies, which is developing both eVTOL and conventional electric aircraft, instead stores liquid coolant in a standalone thermal management system that can be installed alongside its chargers. The system circulates coolant to “pre-chill” the batteries for the duration of the flight, eliminating the added weight of onboard coolant. Competitor Archer Aviation will use the same chargers for its Midnight air taxi.
Keep It Cool
Three groups of five Embry-Riddle students will study both passive heat absorption and active cooling technologies. Their core focus, though, is on phase-change materials, which are designed to convert from solid to liquid at high enough temperatures. During that conversion process, heat is expended, and temperatures do not rise.
“It’s like you’re melting an ice cube,” Boetcher said. “The ice cube is melting, but the temperature stays the same” until all of the ice has melted.
Researchers believe a slab of phase-change material could be placed beneath the aircraft’s electrical circuit to keep its temperature down. They will study the material using computer simulations and plan to develop prototypes that could be tested in a real-world setting.
It is possible, though, that their learnings may apply largely to future aircraft concepts. For example, Beta, and by extension Archer, already has a network of more than 50 charging sites spread across U.S. airports and FBOs in more than 20 states. With that infrastructure in place, major design changes to their respective cooling systems could be costly and time-consuming.
