Industrial society depends on the introduction of new technology to meet business and consumer needs more efficiently.  But every new technology contains a downside or two.  In the case of unmanned aerial vehicles (UAV’s) one of those downsides is the risk of noise pollution generated by drone motors and rotary blades.  For most commercial activities conducted at worksites with heavy machinery, this issue rarely if ever comes into play. But with more private hobbyists flying UAVs in residential neighborhoods, especially suburbia where expectations of peace and quiet are high, it could soon pose a growing challenge to the drone industry.

Industry defenders have often bristled at the suggestion that drones are any louder than other sources of noise, especially vehicle traffic.  In one study funded by NASA, the authors suggested that consumers are simply more accustomed to hearing traffic noise.  But noise experts disagree.  The problem isn’t really the decibel level of the noise but its frequency.  Drone noise is “broadband,” not “tonal,” and can pierce through other sources of noise.  Large package delivery drones – which are expected to come on line over the next couple of years – will be even noisier than common recreational drones, these experts say.  A real solution needs to be found.

To date, drone manufacturers and consumers have come up with a variety of means to lessen their drone noise.  For example, retrofitting drones with larger slower-spinning propellers that are less noisy is one solution.  Another is to cover drone propellers with shrouds that muffle their noise.  In addition, the design and shape of the drone as well as its propellers can greatly affect the noise level.  More silent acoustic signature propellers can reduce the noise by 60% or more.  For instance, the DJI Mavic Pro deploys a propeller known as  the “raked wingtip” to reduce drone noise.

These solutions all have one thing in common: they address drone noise as a hardware problem.  Some next-generation designers are beginning to address the issue as a matter of basic drone design, specifically the drone’s propulsion system.  Mark Moore, former head of Uber’s air taxi division, teamed up with another former member of Uber Elevate to form Whisper Aero, which intends to address the issue at its core.  The challenge is to find new ways to streamline and modulate propulsion without reducing a drone’s lift capacity, which is fundamental to all flight.  Moore thinks he has found a solution – an electric thruster that blends the noise emitted from large delivery drones and small recreational drones into “background” levels of noise – noise, in theory, that is imperceptible to the human ear.

According to Moore, the key challenge is no longer technical but financial – getting his breakthrough invention down to an acceptable level of cost.  Currently financed with $8 million of investment capital, the new system could apply to lots of land-based propulsion vehicles also, Moore believes.  Assuming the invention’s testing remains on schedule, Whisper Aero intends to seek a patent for it by the end of this year.

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