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Urban-Air Port Founder Pitches Solution To eVTOL Downwash, Outwash

The Vertical Airfield is designed to mitigate the harmful effects of eVTOL downwash and outwash.

Credit: Urban Air-Port

A report published by the FAA in December has caused many in the advanced air mobility (AAM) industry to reassess assumptions about the safety impacts of downwash and outwash produced by electric vertical-takeoff-and-landing (eVTOL) vehicles.

Troublingly, the report concluded that downwash and outwash (DWOW) flow fields produced during testing with eVTOL aircraft from Archer, Joby and Volocopter caused high-velocity, hurricane-force winds up to 100 mph that could “easily go beyond the safety area of a vertiport.”

Manufacturers including Archer and Joby have pushed back against the report’s conclusions, arguing that it failed to provide baseline measurements with an existing helicopter for comparison, among other complaints. Previous tests show that DWOW produced by a Robinson R44 light helicopter were roughly similar to that of an eVTOL, Joby says.

Others have taken a dimmer view of the FAA’s findings. Ricky Sandhu, founder of London-headquartered vertiport startup Urban-Air Port, believes that the FAA’s report actually understates the extent of the risk from eVTOL DWOW.  Among other issues, he criticizes the agency’s methodology–including its reliance on computational fluid dynamics (CFD), among other issues—as insufficient to accurately modeling the effects of DWOW. He also argues that the FAA did not include enough test sensors to fully capture the downwash's complexity and magnitude.

Moreover, he says the FAA’s updated guidance in Engineering Brief 105A, published in January, does not go far enough to protect against the magnitude of DWOW identified in its own report. He says that results from Urban-Air Port’s internal modeling, which uses a vorticity transport modeling approach rather than CFD, were “more extreme” than what the FAA reported.

“We’re glad to see the FAA finally recognizing DWOW as a serious issue, but we think that what they’ve published is actually massively insufficient,” Sandhu tells Aviation Week. “Had they gone further, they would better understand the extremely complex interactions of each rotor and its downwash and outwash interacting not only with the ground, but also with adjacent rotors’ downwash. We’ve done all of that using a complex vorticity transport model, and we think the true impact is even more severe than what they’ve found.”

Sandhu predicts that many vertiport developers will run into worse-than-anticipated DWOW effects that will gravely limit eVTOL throughput, and by extension, revenues and profits, posing a threat to the urban air mobility (UAM) business model which depends on high-volume operations to drive down fares to a level competitive with ground transportation.

While addressing DWOW remains a challenge, Sandhu believes that Urban-AirPort’s patented Vertical Airfield concept would substantially mitigate its harmful effects. The concept features an elevated takeoff-and-landing zone that automatically raises itself up to 15 m (49.2 ft.) above ground level for takeoffs and landings, allowing for a totally insulated passenger area below. Adjacent to the elevated final approach and takeoff area are a series of modular vehicle stands that double as hangars and MRO and charging facilities. Besides protecting passengers from the harmful effects of DWOW, the Vertical Airfield concept also reduces a vertiport’s total footprint, simplifying the challenge of securing expensive real estate in downtown urban areas.

“These are high-speed, highly complex and highly dangerous vortices, and it’s going to be insanely dangerous when you put these vertiports in downtown locations,” Sandhu said. “To land in a high-density location, you’ve got to solve these challenges the FAA has highlighted. Otherwise, you’re going to have to land in a low-density area and your entire business case quickly unravels.”

Since the publication of the FAA’s study, Sandhu says that Urban-Air Port has seen a moderate uptick in interest in the Vertical Airfield. “We’ve had several large OEMs contact us, and they are starting to understand the consequences” of DWOW, he says.

It seems like others in the industry have already arrived at a similar conclusion. In China, EHang recently published a video on LinkedIn that showed an EH216-S autonomous eVTOL taking off from what it described as a fully automated “vertical lift vertiport” in Shenzhen’s Luohu District that bears a striking resemblance to the Vertical Airfield concept.

“Kudos to them, but they are seemingly infringing on a patent,” Sandhu says. “We’ll take that up separately. But the important thing is that public recognition is growing, we have our technology in place, and we’re excited to showcase it.”

Ben Goldstein

Based in Boston, Ben covers advanced air mobility and is managing editor of Aviation Week Network’s AAM Report.