Air taxi proposals face a perfect storm of safety concerns in our cities, as lighter aircraft flying and landing at low altitudes are more susceptible to wind gusts and turbulence caused by high-rise buildings and infrastructure in cities.
Researchers at RMIT University in Melbourne are calling for certification of aircraft and design rules for landing sites to address the risks of air accidents due to wind gusts. They have a paper recently published in Drones.
Turbulence and wind gusts are a leading cause of air accidents, and affect aircraft of all sizes, the paper says.
Advanced air mobility proposals – involving large fleets of light electric aircraft carrying passengers and/or freight over multiple flight paths and landing sites in urban environments, including landing on high-rise buildings – are at greater risk due to a combination of factors.
According to the paper, the smaller, lighter and faster an aircraft, the more susceptible it is to wind gusts and turbulence.
Aircraft flying at lower altitudes in urban environments are subject to higher turbulence due to buildings and other infrastructure, which can cause wind gusts and turbulence affecting the air space up to several kilometres away.
“Under even moderate winds, landing and take-off manoeuvres are subjected to high levels of turbulence intensities and gusts that will impact the stability and control of these vehicles,” the paper says.
“Aircraft collisions with high-rise buildings [are] not unheard of,” the paper says.
Advanced air mobility proposals increase the risk of collisions as greater numbers of vehicles seek to navigate complex environments.
Lead researcher and aerospace engineer Dr Abdulgani Mohamed says he is “keen to jump into an air taxi myself so long as I know it’s been designed safely and all the right measures have been taken.”
In their paper, the researchers explored and measured the wind conditions around a representative building in the northern suburbs of Melbourne, simulating worst case wind gust conditions for different models of aircraft.
“Over a very short amount of time, there’s a significant force that can be generated, as an aircraft flies through what we call shear layers,” Mohamed says.
There have been various proposals for ‘air taxis’ in Australian cities.
Wisk Aero and Queensland mayors plan to deliver air taxis in time for the 2032 Olympics, while Uber Air, followed by Eve and Microflite announced plans in Melbourne.
The researchers’ findings have important implications for vehicle certification, heliport planning and design, as well as aircraft operations.
Before any advanced air mobility proposals get off the ground, the paper says there needs to be stronger aircraft certification requirements, including “the ability to counter attitude disturbances and flight path deviations for a reasonable range of wind speeds and gust conditions to make [advanced air mobility] operational for the majority of the year despite weather”.
“Limits should also be imposed on how much flight-path drift occurs for a range of wind and gust speeds, to reduce risk of collision with infrastructure,” the paper says.
Mohamed says he hopes the research provides a useful dataset for the vehicle manufacturers in their design processes. But he adds that wind patterns are unpredictable and change over time, and can be affected by the operation of aircraft (which leave a wake) or the construction of new buildings.
The results of the study also have implications for the design of landing infrastructure, which the advanced air mobility sector call ‘vertiports’.
Mohamed says he has been invited to join a Civil Aviation Safety Authority panel focussing on the design of vertiports to avoid creating challenging wind gust and turbulence conditions, and features that might mitigate dangerous conditions such as rounded corners and wind deflectors.
The paper explains vertiport planning will need to include site-specific wind simulations and measurements including a thorough understanding of wind flow and gusts. Design will need to avoid features that make turbulence worse.
“Currently there appears to be negligible certification or regulation for AAM systems to ensure safe operations when traversing building flow fields under windy conditions and it is hoped that the insights provided in this paper will assist with future certification and regulation,” the paper says.
New weather observation frameworks will also be needed to support operations to ensure flying is safe and reliable, as current systems are designed for aircraft flying at high altitude.
“I think there’s more work required in this area. But I think if there’s more collaboration between academia and industry, then hopefully we’ll get this technology safe and ready for us to use,” Mohamed says.
The research was conducted in collaboration with the University of Maryland and Lehigh University, and was funded by the US Airforce Office for Scientific Research and DSI Group.
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