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Engineers Design a Quieter Future for Drones and Flying Cars

One obstacle to realizing the imagine flying cars is noise-imagine 1,000 leaf blowers intruding over your backyard barbecue.

It’s not only flying cars but for drones as well. Complaints about the high-pitched keening of propellers could lead to restrictions or regulations that may hamper the growth of the new commercial drone industry.

University of Cincinnati aerospace engineering students are studying methods to dampen sound in assistant professor Daniel Cuppoletti’s lab in UC’s College of Engineering and Applied Science. If flying cars are to succeed, Cuppoletti said, they’ll need to be quiet.

UC aerospace engineering students Natalie Reed, Matthew Walker and Peter Sorensen presented papers with Cuppoletti in the Science Forum and Exposition this month in San Diego, California. Hosted by the American Institute of Aeronautics and Astronautics, it’s the world’s largest aerospace engineering conference.

“I’m exploring the noise from a societal impact,” Cuppoletti said. “These vehicles need to be imperceptible in the environment they fly in or someone will need to go ahead and take brunt of that impact.”

Too often, the impact is felt in lower-income neighborhoods, he explained.

Airports across the nation would be the subject of tens of thousands of noise complaints per year filed by aggravated residents. Within an FAA survey published last year, two-thirds of respondents said they were “highly annoyed” by aircraft noise. Noise from planes and helicopters was a much bigger annoyance than cars, trucks, or neighbors, the survey found.

Likewise, engine noise is a big concern of military and commercial aviation. Hearing problems and tinnitus are the leading causes of medical disability claims filed using the U.S. Department of Veterans Affairs.

Drones don’t pose exactly the same risk for hearing problems as bigger aircraft because they’re very little louder than a kitchen appliance. However the unique quality of their buzzing rotors stands out against the ambient background, causing them to be irritating and distracting.

“One helicopter flying over your homes roof could keep you up,” Cuppoletti said. “If you would like 1,000 drones flying over cities in urban centers, the noise is a huge problem.”

A potential aggravating factor is a sheer scale. As the United States sees about 5,700 commercial aircraft flights every day, drones with their diverse applications have the possibility for a large number of flights in main urban centers each day.

Cuppoletti said a number of factors modify the way people perceive sound. Aircraft noise is way less noticeable in congested cities than in suburbs or countrysides. And also the time of day matters as well. Evenings are usually quieter, making aircraft more noticeable.

“Research has discovered that just seeing an aircraft may cause individuals to think they’re loud,” Cuppoletti said. “There are subjective human factors you can’t control.”

Cuppoletti is studying how you can manipulate sound from drones through engineering design. He tests sound inside a room lined with sound-absorbing padding that eliminates echo.

Using an anechoic chamber, a room covered on every side by sound-dampening material and outfitted having a suite of eight microphones, Cuppoletti tests the regularity, wavelength, and amplitude of sound, among other factors affecting our perception of noise. He and his students are creating a guidebook that manufacturers of drones and flying cars can use you may anticipate what their novel designs will sound like based on UC’s engineering and physics experiments.

Every rotor has its own noise signature. Simply changing the configuration of two rotors can add or reduce sound by 10 decibels or even more, UC student Reed said.

She tested 16 rotor configurations and presented them at the SciTech conference.

“Changing the vertical gap influences the noise. So I looked at what goes on if we change the vertical or horizontal spacing,” she said.

UC student Sorensen studied variations in sound in rotors rotating in the same direction versus opposite directions: Co-rotating or counter-rotating. To date, the outcomes are inconclusive.

With flying cars taking wildly imaginative forms around the drawing board, UC engineers hope to help create quieter designs.

“This can be a thrilling here we are at aerospace,” Cuppoletti said. “New aircraft designs are in the preliminary and conceptual design stages. We are able to influence what they will seem like based on decisions designers make now.”

UC’s sound experiments will help manufacturers make more informed design decisions, he explained.