Standardization News

Vertical take-off and landing (VTOL) aircraft have come a long way since the groundbreaking, 20-second flight of the Cornu helicopter in 1907. From that first flight in Normandy, France, to the introduction of commercial helicopters in the 1940s and the tilt-rotor Osprey of the 1980s, people have imagined using these vehicles for personal transportation. Advocates have long argued that “air taxis,” as they are colloquially known, would alleviate traffic congestion, reduce the demand for paved infrastructure, and quickly get people to their destinations.

In recent decades, interest has shifted from petroleum-reliant VTOLs to a more sustainable type of air taxi that has the flight benefits of airplanes and the landing advantages of helicopters: electric vertical take-off and landing (eVTOL) aircraft. Powered by battery packs, eVTOLs promise zero emissions and reduced noise pollution along with the perks of traditional VTOLs. As major manufacturers and startups set their sights on eVTOL production, the dream of the air taxi may soon become reality.

In July 2023, the U.S. Federal Aviation Administration (FAA) further advanced the air taxi concept with its plan to integrate eVTOLs and other electric aircraft into existing U.S. air infrastructure by 2028. The FAA has also granted special airworthiness certificates to eVTOL producers Archer and Joby Aviation for flight testing their air taxis. Outside the U.S., the German urban air mobility (UAM) startup Volocopter will be the first to undergo European Union Aviation Safety Agency (EASA) certification of its eVTOL. Volocopter plans on global distribution of its electric aircraft and the launch of commercial air-taxi service in 2024.

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Helping to ensure that eVTOLs have sound infrastructure, including a suitable structure for take off and landing, is ASTM International’s new subcommittee on unmanned air systems (UAS) infrastructure (F38.04), created in the summer of 2023. Infrastructure refers to the UAS traffic-management system as well as the physical architecture: vertiports. As defined by ASTM’s standard specification for vertiport design (F3423), a vertiport is the area of land, water, or structure used for the landing and takeoff of VTOL aircraft. It includes any associated buildings and facilities.

“One reason we have the infrastructure subcommittee is that we need to safely integrate legacy air-traffic management with these new platforms, AAM [advanced air mobility] and UTM [unmanned aircraft systems traffic management],” says Phil Kenul, chair of the committee on unmanned aircraft systems (F38) and an aviation consultant for ASTM. “We have this whole new disruptive technology — the expectation is we will be flying around like the Jetsons in the future. But we have to ensure that it doesn’t interfere with police and EMS platforms at these lower altitudes or expanding package-delivery services from UAS. The subcommittee is working on AAM traffic management and the communication protocols of the provider of services for urban air mobility [PSUs]. Safely de-conflicting all these airspace users will require a new approach to infrastructure.”

To date, the UAS industry has largely covered air-traffic management and has not interfered with the legacy platform, but AAM may ultimately require a different approach, Kenul says.

Vertiports

An obvious assumption regarding where eVTOLs would take off and land is that the aircraft would use existing ground, or elevated/rooftop heliports. However, unlike combustion engine helicopters, eVTOLs require electric-charging infrastructure, which extant heliports do not possess. Furthermore, the lithium-ion batteries that power eVTOLs necessitate a different fire-safety plan. Because these batteries do not need outside oxygen to burn and are prone to reignition, traditional fire extinguishers and foam suppression systems would be ineffective on an eVTOL fire. Access to water, and a lot of it, is key.

“When you look at the criteria used for heliports, a lot is based on a significant amount of history,” says Rex Alexander, president and executive director of Five-Alpha LLC and infrastructure advisor for the Vertical Flight Society.

“The first heliport design circular was published by the FAA in 1959. When we look at the circular [AC 150/5390] from a historical standpoint, it speaks to the fact that helicopters can use heliports because they’re certified as helicopters under CFR Title-14 Part-27 or 29. When you look at the advanced air mobility eVTOL, we have to ensure that, if they’re going to use a heliport, they at least meet or exceed the performance capabilities helicopters are required to meet for certification. However, no one has released any performance data on eVTOLs. What are they capable of and more importantly, what are they not capable of? What are their aerodynamic deficiencies?”

Alexander notes that the average U.S. heliport is designed with a touchdown and liftoff (TLOF) area of 40 x 40 feet or less, which would be undersized for a vertiport based on criteria found in FAA Engineering Brief (EB) No.-105, Vertiport Design.  EB 105, which is based on transport heliport criteria and requires a larger footprint than the average general aviation (GA) heliport. It requires roughly twice the footprint demanded by a GA heliport to accommodate the required clear, unobstructed airspace to support a TLOF, final approach and takeoff (FATO) area, and safety area.

While no customary shape or dimensions currently exist for air taxis, they all share one feature — and one space limitation: wings.

“When you say ‘eVTOL,’ you’re referring to many different designs: powered lift, rotorcraft, fixed wing,” says Jonathan Daniels, ASTM fellow and chair of subcommittee F38.04. He is also the CEO of Praxis Aerospace. “Building something that can handle those performance characteristics is a challenge.”

New standards for vertiports will ensure that eVTOLs have sound infrastructure.

Additionally, there are concerns about use case and public versus private heliports. Presently, the FAA identifies 6,156 heliports in the U.S. in their Airport Data and Information Portal (ADIP) system. Of this number, 54 are identified as public use and do not require prior permission of the owner to be utilized. According to Alexander, based on his independent research, approximately 11 percent of public-use heliports could potentially support an AAM public transportation model using eVTOL aircraft. The rest are constrained by their environs, such as the presence of buildings, wires, antennas, and trees, and the fact that that heliports were never designed for the volume of traffic anticipated from AAM air-taxi operations. Alexander estimates a minimum of 30 eVTOL takeoffs and landings per hour from a single vertiport would allow for a viable business model.

Information and Communication

In F3423, the eVTOL industry has the requirements for planning, designing, and establishing vertiports. But how will it disseminate critical information and manage the air traffic around these sites? To address these concerns, ASTM’s infrastructure subcommittee has drafted the new specification for vertiport automation supplemental data service provider (SDSP) performance (WK85153). The work item defines vertiport automation SDSP services to UAS service suppliers (USS) and providers, UTM operators, and providers of services for UAM, which are also known as PSU. These services will enable such fundamental operations as visual line of sight (VLOS) and beyond visual line of sight (BVLOS) for UAS, and they will also assist in flight planning and go/no-go as well as in-flight decision-making for UAS and UAM.

“This is the information or digital piece, explaining what information will be coming out of, and provided to the users of, the vertiport,” Kenul says. “It could be weather, navigation support, or communication with the FAA when needed. It’s all the information needed to fly in and out of vertiports. The work item came out of a NASA study and will get into both hardware
and software.”

The specification may offer guidance on how to present information to the eVTOL operator, accounting for human factors and situational awareness. It may also support other USS/PSU capabilities, such as geofencing and flight planning for applications that involve UAS and UAM. The work item’s rationale states that it should aid in addressing “risk-based considerations and exemptions, operational certifications, and equipment certifications by enabling determination of bounds on performance that are acceptable by civil regulators.”

To collect this information, vertiports will need to have an assortment of sensors and other instruments on site. These devices would measure and/or report weather conditions, noise levels, hazards, and debris, among other things.

“We refer to the SDSP standard as the hotels.com of vertiports. The idea is you plug into the system or app, and you say, ‘I’m going to fly to this point, and I want to park in this location. Do you have the charging station I need, and will it be available?’” Daniels says.

He adds that the vertiport standard is scalable and can apply to drones, which have similar issues as eVTOLs.

eVTOLs and Advanced Air Mobility

When implementing a new technology such as AAM, all possible challenges need to be explored. For eVTOLs, network connectivity is a good place to start.

“Network connectivity is great when you’re in a place where you have massive redundancy of connectivity. As soon as you go somewhere where it isn’t present and there’s a GPS failure, everything stops,” Daniels says. “With connectivity on the vertiports, we talk about having that redundancy. And if you are disconnected, does the vertiport have an obligation to have that infrastructure so you can still connect, even if it’s just connecting locally?  As long as you’re within line of sight — I can see the vertiport and I’m coming in to land — do I need to have radio, data communications, and those types of things in play?”

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The infrastructure subcommittee will also work to ensure that eVTOLs don’t interfere with ground communications. “We’ve already encountered where 5G has interfered with old radar altimeters. We had to change the rules for helicopters and create new devices to avoid a safety problem. So how can we make eVTOL and drones rely on 5G for connectivity because they have to talk to each other? That’s an area we’re going to look at in 38.04,” Daniels says.

Another concern is the ground movement of eVTOL aircraft, some of which do not possess wheels. “Is the platform being tugged or towed? Is it self-propelled or robotic?” Alexander asks. “If it does have wheels, you don’t want to use up the onboard electricity to move it under its own power, and you definitely wouldn’t want to hover. You want to land and shut down as fast as you can to preserve energy and extend your range.”

Other ground-movement considerations include the minimum turning radius and whether an eVTOL’s wheels will withstand rigorous, daily use.

Regarding UAM specifically, the amount of air space that an eVTOL has to take off and land comes into question. In dense, urban areas, which are the intended market for air taxis, open space is scarce but obstacles are plentiful.

“We have these beautiful renderings of aircraft flying between two buildings, flying completely vertical the entire way. It’s an extremely difficult flight maneuver and, when there’s an emergency, you have no ability to react. The best that you can hope for is up or down. You have to hope you don’t lose control and go sideways, because you’re no longer flying in an urban canyon, you’re dropping down a mine shaft,” Daniels says.

The absence of operational vertiports is likewise a sticking point. Although several U.S., airport-based heliports refer to themselves as vertiports, they do not possess vertiport capabilities. Meeting the performance requirements for vertical takeoff and landing, and the support requirements such as electric charging, are challenges that heliports face in supporting eVTOLs.

Presently, there are no operational vertiports in the U.S., but vertiport beta sites do exist near Paris and in Singapore, Rome, and Coventry. Focused on one-off demonstrations, they are not set up for routine eVTOL flights.

Regular eVTOL flights are on the horizon, though. Residents of Orlando, Florida, anticipate the completion of the Lilium Lake Nona Vertiport by 2025. Created in partnership with the German aviation company Lilium and the city of Orlando, the vertiport would serve as an AAM hub and support eVTOL travel for over 20 million people within a 186-mile radius.

For additional information about the UAS infrastructure subcommittee (F38.04) or to join the group, please contact staff manager Mary Mikolajewski at mmikolajewski@astm.org. ■

Kathy Hunt is a U.S. East Coast-based journalist and author.