Whatever flies is subject to the vagaries of weather, some more than others. Aircraft can fly through hurricanes if the planes are built for that purpose. Don’t try that with a Cessna or Piper general aviation plane. Or a hot air balloon! Design is critically important in aviation and so is construction. Stress can cause metal failure in an aircraft as well as mental failure in a pilot. Either one can cause a catastrophe.
While we haven’t reached the Jetson’s level of personal flying cars, the air taxi industry is on the verge of taking flight as major companies like Boeing, Hyundai, Airbus, and Toyota are actively developing fleets to facilitate seamless commuting in the skies. Both Europe and the U.S. have formulated new regulations to establish a framework for air taxi operations to commence within the next decade. And, like everything that improves what we do, air taxis will require specific infrastructure changes to be both safe and practical.
In urban areas, where air taxis will be most in demand, where will they take off and land? Current projections are that roofs of tall buildings will be the homes for vertical takeoff and landing vehicles as they are now for helicopters. The problem is tall buildings are, by their nature, disrupters of air flow. Watch the snow swirl at different levels between buildings in New York or Chicago and that becomes obvious.
In recent years, there has been a significant advancement in conducting intricate studies on the impact of sudden wind gusts around urban structures and their potential to destabilize aircraft. For example, RMIT University’s UAS (uncrewed aircraft systems) research team recently published a paper highlighting their findings in this area.
According to Abdulghani Mohamed, Phd., who conducted the research at RMIT, low-flying aircraft are particularly vulnerable to wind gusts due to their slower landing and takeoff speeds. The study showed sudden wind gusts can present significant safety obstacles for air taxis and drones in less than a second. Consequently, air taxis and drones will require additional power during their landing or takeoff maneuvers in urban environments, in contrast to airports or open spaces.
Across the globe, regulations are being proposed pertaining to AAM (advanced air mobility) aircraft, including air taxis. Both the U.S. and Europe are actively involved in compiling these regulations. RMIT emphasizes that regulations and certification processes should specifically focus on ensuring the safe operation of air taxis and drones when navigating through the flow fields created by buildings.
In determining the placement of vertiports, which serve as the takeoff and landing locations for these vehicles, it is imperative that hazardous regions are identified and avoided. This approach would enhance safety, mitigate potential disruptions caused by adverse wind conditions, and contribute to the smooth operation of the air taxi fleet.
Air taxis will require weather information at significantly higher resolution and faster rates than what is presently achievable. This is crucial for effective flight planning and operational decision-making. The margin of error for air taxis in cities will be significantly lower compared to airports, as larger aircraft can tolerate stronger gusts. By designing purpose-built vertiports, geometric features that can minimize the occurrence of hazardous airflow conditions can be incorporated.
Building for the (Near) Future
While existing buildings can be repurposed as vertiports, certain modifications might be necessary to enhance aerodynamics near the landing pads. The effectiveness of these design features can be evaluated through scaled experiments conducted in wind tunnels or through full-scale measurements. Combining that with digital twin models of existing buildings should benefit the industry.
The air taxi industry, once it begins, will be initially operated by human pilots with specific training. Eventually, based on contemporary trends, those air taxis will be “piloted” by AI (artificial intelligence). Autonomous flying vehicles are not new but have been restricted to uncrewed operations. The popular UAS or drone is an example. And while drones for surveying, photography, search and rescue, and infrastructure inspection and maintenance are becoming common sights, they are still predominantly operated by ground-based pilots.
The advent of advanced air mobility vehicles involves operating fleets of UAVs in urban environments far more frequently than ever anticipated, for the purpose of transporting parcels and passengers. This exposes the fleet of aircraft to a wide range of challenging flow conditions; specifically large-scale gusts induced by urban infrastructure, which can persist up to several miles away from the source and interact in complex ways. AAM flights will often involve operation in close proximity to physical structures (inspection of infrastructure, or take-off and landing operations from building rooftops). In the presence of large-scale gusts, significant flight path deviations can occur, increasing risk of collision with objects.
Conflicts and Customers
It seems like a natural evolution to leverage airspace for urban mobility, yet challenges abound—infrastructure and regulatory constraints, as well as technological—but the biggest challenge might be to prepare consumers for this new reality.
Deloitte’s 2019 global automotive consumer survey showed consumer perception towards AAM, particularly concerning safety, continues to lean toward concerns. This is despite the substantial progress made in terms of vehicle design and technology, including advances in eVTOL (electric vertical takeoff and landing) aircraft. The survey data also shows regional and generational differences play a critical role in the perceived safety of AAM.
While surveyed consumers agreed air taxis could be possible solutions to solve roadway congestion, concerns about these vehicles’ safety have slightly increased. This comes despite increased awareness by consumers about the utility and safety of AAM. Forty-eight percent of survey respondents were unconvinced about the safety of air taxis in 2019, compared with only 46% in 2018. This seeming contradiction of consumers perceiving increased utility, but decreased safety could be attributable to their notion of utility “in future” versus safety “now.”
Aircraft collisions with high-rise buildings are not common but certainly not unheard of and the routine operation of UAVs in cities further increases the risk of collisions. There is a need for both research and regulation efforts to enhance safety and minimize the risk through considering vertiport and vehicular design.
The most common AAM is still the helicopter, which also flies in urban environments but less frequently and with a human pilot onboard. After decades of landing on buildings, the operation still poses a specific challenge, in some cases warranting further aerodynamic studies and field wind measurements for safety. From a design standpoint, the AAM flight dynamics are different from the conventional helicopter or airplane, which requires exploration into novel design features and technologies to enable lower sensitivity to turbulence and precise maneuvering.
From a vertiport standpoint, the existing heliport infrastructure can potentially support AAM; however, there is a need for purpose-built buildings for ease of public access and to account for the autonomy of UAVs. The character of the flow fields for different wind conditions around vertiports must be analyzed in ways like those conducted for heliports.
For urban air mobility vehicles to be viable, they must be able to overcome the turbulence in different seasonal conditions, so that they can operate all year round. The UAVs require a large power reserve, as well as a large open space for take-off and landing, to allow room for the propellors to respond to wind conditions and correct the drone’s flight path. Also, as the drone travels to and from its vertiport, the vertiport itself needs to be designed to minimize turbulence. Currently, there is a lack of published research on the best vertiport design, or which building shapes result in minimal turbulent flows.
Simulations show how urban environments offer a unique set of challenges for UAVs due to the turbulent flows generated by infrastructure. Current designs are susceptible to these gusts in specific scenarios and may not have the response times necessary to overcome these flows. While there are exciting possibilities for the development of these technologies, further work must be done to ensure the steadiness of the UAVs and the safety of deliveries and future passengers. The view of Jetson-like flying cars dotting the skies is still found most often in animated films or Star Wars. But that can be changing rapidly so the newer buildings and infrastructure in urban areas should start to look like it can sustain those air taxis and Amazon delivery drones being talked about.
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