As cities prepare for a future filled with drone deliveries and flying taxis, researchers have discovered an unexpected solution to one of the biggest challenges facing urban aviation: grass. A pioneering study from the University of Bristol has shown that simple vegetation can significantly reduce the noise from aircraft landings, potentially changing the way we design urban landing sites of the future.
The study, published today in Scientific Reports, shows that porous surfaces such as grass can reduce low- and mid-frequency noise from drones by up to 30 decibels, a significant reduction that could influence widespread public acceptance and rejection of urban air transportation. .
“While noise problems are well documented, solutions for urban environments are limited,” said Hasan Kamriya Jawahar of Bristol’s School of Science and Engineering, who led the study. Dr. Kamliya Jawahar explains. “I drew inspiration from naturally porous materials, such as vegetation, which are known for their noise-reducing properties. This led to the exploration of engineered porous surfaces as a potential solution to reduce noise and improve aerodynamics.
These findings aren’t just about noise reduction—research shows these surfaces can actually improve the performance of aircraft propellers. This dual benefit is critical to the burgeoning urban air mobility industry, as efficiency and community acceptance go hand in hand.
To test their theory, the team conducted experiments in an anechoic chamber, a room specifically designed to completely absorb sound reflections. They installed a propeller on different surfaces, alternating between solid materials and porous treatments of varying thicknesses.
The science behind this noise reduction is fascinating. As Dr. Kamliya Jawahar explains: “Vegetation is known to function as a natural porous medium, with its structural complexity and material properties such as leaf density and moisture content contributing to its ability to absorb noise.”
As a drone or flight taxi approaches a porous landing surface, vegetation absorbs energy from the air pushed downward by the propeller. This reduces the speed of what scientists call a “tangential wall jet”—essentially a high-speed stream of air that is typically shot along a solid surface during landing.
The porous structure also traps some of the turbulent air, preventing it from bouncing back onto the propeller—a major source of noise in current drone operations. This combination of effects results in a significant reduction in noise during landing.
The impact on urban planning is significant. Future vertiports — proposed landing spots for flying taxis and delivery drones — could incorporate grass, moss or engineered porous materials into their designs. This can help these facilities meet strict city noise regulations while improving their environmental impact.
“Our research shows that innovative porous landing surfaces can significantly reduce the noise from drones and air taxis, paving the way for quieter, more sustainable urban skies,” said Dr. Kamriya Jawahar.
The solution builds on existing environmental noise reduction strategies. While vegetation has long been used for roadside barriers and urban green spaces, this marks the first time its use in urban air mobility applications has been scientifically investigated.
As cities around the world grapple with the challenges of integrating flying machines into urban life, this research suggests that some of the solutions may be growing beneath our feet. The future of urban air mobility will not only be quieter, but also greener in every way.
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