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Simple Grass Could Be the Secret to Silent Flying Taxis

As cities prepare for a future filled with drone deliveries and flying taxis, researchers have discovered an unexpected solution to one of urban aviation’s biggest challenges: grass. A groundbreaking study from the University of Bristol reveals that simple vegetation could dramatically reduce the noise from landing aircraft, potentially transforming how we design tomorrow’s urban landing pads.

The research, published today in Scientific Reports, demonstrates that porous surfaces like grass can cut drone noise by up to 30 decibels in low-mid frequencies – a significant reduction that could make the difference between widespread public acceptance and rejection of urban air mobility.

“While noise issues are well-documented, solutions tailored to urban environments are limited,” explains Dr. Hasan Kamliya Jawahar from Bristol’s Faculty of Science and Engineering, who led the research. “I drew inspiration from natural porous materials, such as vegetation, known for their noise-damping properties. This led to exploring engineered porous surfaces as a potential solution to reduce noise and improve aerodynamics.”

The findings aren’t just about noise reduction – the research shows these surfaces can actually enhance the performance of aircraft propellers. This dual benefit could prove crucial for the emerging urban air mobility industry, where efficiency and community acceptance go hand in hand.

To test their theory, the research team conducted experiments in an anechoic chamber, a specialized room designed to completely absorb sound reflections. They mounted a propeller above different ground surfaces, alternating between solid materials and porous treatments of varying thickness.

The science behind this noise reduction is fascinating. As Dr. Kamliya Jawahar explains: “Vegetation is known to function as a natural porous medium, where its structural complexity and material properties such as foliage density and moisture content contribute to its noise absorption capabilities.”

When a drone or flying taxi approaches a porous landing surface, the vegetation absorbs energy from the air being pushed downward by the propellers. This reduces the speed of what scientists call the “tangential wall jet” – essentially a high-speed blast of air that normally shoots out along solid surfaces during landing.

The porous structure also traps portions of this turbulent air, preventing it from bouncing back up into the propeller – a major source of noise in current drone operations. This combination of effects leads to significantly quieter landings.

The implications for urban planning are significant. Future vertiports – the proposed landing sites for flying taxis and delivery drones – could incorporate grass, moss, or engineered porous materials into their design. This could help these facilities meet strict urban noise regulations while improving their environmental impact.

“Our research demonstrates that innovative porous landing surfaces can drastically reduce noise from drones and air taxis, paving the way for quieter and more sustainable urban skies,” notes Dr. Kamliya Jawahar.

This solution builds on existing environmental noise reduction strategies. While vegetation has long been used in roadside barriers and urban green spaces, this marks the first time it’s been scientifically investigated for urban air mobility applications.

As cities worldwide grapple with the challenges of integrating aerial vehicles into urban life, this research suggests that part of the solution might literally be growing under our feet. The future of urban air mobility could be not just quieter, but greener in every sense of the word.


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