Two hybrid-electric aircraft developers, XTI Aircraft and Airflow Aero, have selected VerdeGo Aero’s diesel-battery powertrain to power vehicles intended primarily for cargo applications.
Airflow is developing hybrid-electric short takeoff and landing (eSTOL) aircraft that require a 300-foot runway, intended for middle-mile logistics missions, as CEO Marc Ausman told eVTOL.com in November. The Airflow team, which includes numerous former members of Airbus’ Vahana eVTOL technology demonstrator, believes the development and operating costs of eSTOL aircraft offer significant benefits over VTOL and have many market applications that don’t require vertical lift.
“Our first production aircraft will be hybrid-electric in order to meet range and turnaround time requirements, then move to fully electric when the technology allows,” a representative for Airflow told eVTOL.com.
XTI Aircraft, which continues to develop its VTOL TriFan 600 passenger aircraft, will use VerdeGo’s powertrain on a smaller TriFan 200 model for logistics missions.
Both XTI’s TriFan 200 and Airflow’s eSTOL design will use VerdeGo’s diesel hybrid system, which combines a 180-kilowatt generator with a battery pack to reduce emissions by 35 percent and operating costs by 40 percent compared to conventional turbine powertrains, according to the company, while offering “four to 10 times” the range of a battery-electric system. VerdeGo announced last month it had validated the “Iron Bird” prototype of the powertrain, developed in partnership with Continental Aerospace Technologies, at power output levels above 150 kilowatts.
Eric Bartsch, CEO and co-founder of VerdeGo, and other leaders of hybrid-electric aerospace startups emphasize the advantages of hybrid-electric aircraft over fully-electric designs, seeing fewer barriers to entry-into-service and more useful range and payload capacity in the near term.
“Why have so many urban air mobility startups emphasized battery-only solutions? I think, unfortunately, it’s because a lot of people aren’t doing the math and don’t understand the physics,” said Bartsch on a panel co-hosted by the Café Foundation and the Vertical Flight Society in August. “The fact is, the math doesn’t work for a lot of these market segments for batteries right now. The math will work in 20 years, but we don’t want to wait.”
Saleem Zaheer, XTI’s vice president for global business development, wrote in a blog post that reduced or eliminated need for ground charging, all-weather capability and profitability not dependent on autonomous operation mean that “hybrid-electric VTOL aircraft will attain quicker entry into service and greater deployment in all use cases other than the very short hops possible by all-electric eVTOLs.”
Advocates of fully electric solutions disagree on the “math” — seeing hybrid solutions as more complex and costly systems that won’t de facto win the race to certification — but also hold different views on where the demand for transportation lies, which may in part explain differing approaches in the industry.
“The real answer is because hybrid isn’t needed where the vast majority of trip opportunity exists, and hybrid results in a more complex, heavier and costlier aircraft for UAM missions,” Mark Moore, chief scientist at Uber Elevate, wrote on LinkedIn in response to Bartsch’s statement. “Look at trip range distribution and it’s clear there are 20-50 fold more trips conducted at 15-100 mile distances than at 200+ mile trips, and 100 mile trips with battery eVTOL with reserves is already possible.”
Eric Allison, head of Uber Elevate, told Aviation Today earlier this year the ride-hailing giant extensively analyzed hybrid, hydrogen and fully electric aircraft, concluding that the latter results in numerous ecosystem-wide benefits, including concerns related to using liquid jet fuel at sites where demand would be high.
Without breakthrough advancements in battery technology, the energy density of lithium-ion cells has historically increased by three to five percent annually. Only time will tell where the majority of demand lies, but for missions requiring greater range and/or payload capacity, hybrid propulsion systems are likely to find their way onto both fixed-wing and VTOL aircraft projects.