Commentary by Tomas Pribanic of Undefined Technologies: Would commercial drones overcome noise restrictions for the same-hour delivery?

In this com­men­tary by Tomas Prib­an­ic, Founder and CEO of Unde­fined Tech­nolo­gies, he explores the prob­lem of noise pol­lu­tion and urban restric­tions for drone deliv­ery.

The com­pa­ny is a Flori­da-based tech start­up devel­op­ing its first-ever silent eVTOL drone pow­ered by ion propul­sion. In April, it had a suc­cess­ful first mis­sion flight.

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Three years ago, Bonython, a town­ship in south­ern Can­ber­ra, Aus­tralia, was the site of a new drone deliv­ery ser­vice deployed by Google spin-off Wing. Ini­tial­ly, res­i­dents cheered the last-mile food deliv­ery.

The com­pa­ny even planned to expand its ser­vice, but the tri­al caused anger among the res­i­dents. Some locals soon became both­ered by the con­tin­ued noise of the drones and com­plained.

Res­i­dents cit­ed con­cerns about the impact of drone noise on wildlife. Oth­ers cit­ed migraines and wor­ried the noise would wors­en their med­ical con­di­tion. “With the win­dows closed, even with dou­ble glaz­ing, you can hear the drones,” one res­i­dent told ABC News.

The issue reached a boil­ing point when sev­er­al res­i­dents began threat­en­ing to shoot the drones out of the sky. As a result, Wing had to mod­i­fy the blades used on its drones and began ran­domis­ing routes from the depot and to indi­vid­ual homes so that no one area was bear­ing the brunt of a drone noise cor­ri­dor.

Aus­trali­a’s expe­ri­ence shows the rapid deploy­ment of drones with­out proac­tive noise map­ping or mod­el­ing can incite sig­nif­i­cant com­mu­ni­ty back­lash and reg­u­la­to­ry response. Could this sce­nario repeat in the US? The answer would prob­a­bly be ‘yes.’

As major retail­ers accel­er­ate the deploy­ment of drones in urban areas, we will see high­er demand for autonomous­ly oper­at­ed drones that must com­ply with fed­er­al and coun­ty reg­u­la­tions and ordi­nances. 

Wal­mart recent­ly announced its sig­nif­i­cant invest­ment in Drone­Up, the nation­wide on-demand drone deliv­ery provider, while Ama­zon is build­ing their own unmanned air­craft. In 2020, Amazon’s PrimeAir fleet received FAA approval to com­mer­cial­ly oper­ate drones.

Noise Mat­ters

As drone tech­nol­o­gy takes flight, the world will be get­ting much loud­er – as if ‘neigh­bor­hoods were filled with leaf blow­ers, lawn­mow­ers and chain­saws.’ Drones’ dis­tinc­tive and irreg­u­lar buzzing sound remains an unre­solved issue.

Research con­duct­ed by NASA in 2017 and a fol­low-up analy­sis pub­lished in 2018 found that drone noise ranks high­est in terms of annoy­ance. Accord­ing to the study, the noise made by road traf­fic was “sys­tem­at­i­cal­ly judged to be less annoy­ing” than the high-pitched buzzing made by drones.

Par­tic­i­pants were not told the noise they were hear­ing was from drones. Still, all lis­ten­ers con­sis­tent­ly rank drone noise as more annoy­ing than noise from air­planes or deliv­ery vehi­cles due to psy­cho-acousti­cal prop­er­ties not eas­i­ly mod­elled or cap­tured by tra­di­tion­al acousti­cal met­rics.

A year lat­er, the Nation­al Acad­e­mies of Sci­ences, Engi­neer­ing, and Med­i­cine was approached by NASA to eval­u­ate aer­i­al mobil­i­ty’s ben­e­fits and dis­rup­tive effects, includ­ing drones. Their pre­lim­i­nary find­ings, released in the spring of 2020, call for fur­ther research into pub­lic annoy­ance asso­ci­at­ed with drone noise.

No Reg­u­la­tions

Despite the dif­fer­ent noise ordi­nances estab­lished by coun­ties in the US, no clear reg­u­la­to­ry frame­work exists at the fed­er­al lev­el to mon­i­tor any noise in urban areas.

This year, con­gres­sion­al law­mak­ers already announced plans to re-intro­duce the Heli­copter Safe­ty Act on Capi­tol Hill to ban non-essen­tial heli­copter flights over New York City. The mea­sure was orig­i­nal­ly intro­duced in 2019, and aims to mit­i­gate heli­copter traf­fic and noise pol­lu­tion.

Noise map­ping could bring more clar­i­ty to the sit­u­a­tion. In the Unit­ed States, noise map­ping is only com­mon at a project-lev­el scale for spe­cif­ic sound sources such as air­ports, man­u­fac­tur­ing, com­mer­cial facil­i­ties, and high­ways since no law or reg­u­la­tion requires mon­i­tor­ing region­al noise.

How­ev­er, at a larg­er scale, region­al noise maps are more com­mon in Europe due to EU Direc­tive 2002/49/EC, which requires region­al noise maps in areas with high pop­u­la­tion den­si­ties.

There are just a few region­al noise maps in the US. For exam­ple, the Nation­al Park Ser­vice (NPS) has col­lect­ed data from its parks across the Unit­ed States. The NPS has paired these data with sev­er­al envi­ron­men­tal, human activ­i­ty, and topog­ra­phy maps to mod­el anthro­pogenic noise and nat­ur­al sound. The Volpe Cen­ter also released its Nation­al Trans­porta­tion Noise Map in 2017, rep­re­sent­ing the first nation­al trans­porta­tion noise dataset avail­able to the pub­lic.

Health & Well-being Impact

Sci­en­tists esti­mate that a sin­gle drone can make an area 8 to 12 times loud­er than it is now. Seri­ous com­mer­cial drones have eight or more pro­pellers (Wing has 14; Amazon’s Octo­copter has eight pro­pellers spin­ning at thou­sands of rev­o­lu­tions per minute, phys­i­cal­ly beat­ing the air to gen­er­ate lift and move­ment). The heav­ier the load, the hard­er the drone must work, the more air gets beat­en, the loud­er the sound emit­ted.

With­out inno­va­tion and reg­u­la­tion, the buzzing of drones may soon fill the city and sub­ur­ban skies – adding to the din in many places and dis­turb­ing the peace of even those wealthy sub­urbs whose res­i­dents can afford the con­ve­nience of rapid home deliv­ery. Even neigh­bour­hoods that have man­aged to avoid being under air­port flight paths will find them­selves sur­round­ed by the buzz.

Com­mer­cial drones could turn a qui­et day into some­thing dif­fer­ent. It’s not just loud­ness. Drones have rel­a­tive­ly small pro­pellers, which don’t move much air, but move rapid­ly. The speed of the spin­ning equates to its fre­quen­cy.

Adding a pay­load to a drone means the pro­pellers must put more ener­gy into the air by spin­ning faster – mak­ing a loud­er and high­er-pitched sound. The fre­quen­cies they gen­er­ate are, in fact, the same fre­quen­cies peo­ple are most sen­si­tive to.

“Imag­ine tens or even hun­dreds of drones buzzing around your neigh­bor­hood, deliv­er­ing pack­ages to homes and busi­ness­es,” says Garth Paine, Asso­ciate Pro­fes­sor of Dig­i­tal Sound and Inter­ac­tive Media, Ari­zona State Uni­ver­si­ty, in his arti­cle Drones to deliv­er con­stant buzzing noise, and pack­ages.

“Next, imag­ine the round-the-clock hives of aer­i­al activ­i­ty that ware­hous­es and dis­tri­b­u­tion cen­ters will become, in addi­tion to their exist­ing bur­den on local roads.”

The amount of time a per­son is exposed to dif­fer­ent sound lev­els mat­ters, too. The US Occu­pa­tion­al Safe­ty and Health Admin­is­tra­tion says work­ers exposed to 85 deci­bels or loud­er for eight hours or more may suf­fer hear­ing dam­age or loss. The Fed­er­al Avi­a­tion Admin­is­tra­tion says that res­i­den­tial areas should not have air­craft noise aver­ag­ing above 65dB in a 24-hour peri­od.

Near-Silent Solu­tion

Uber Ele­vate, even in 2016, pre­dict­ed that “new noise expo­sure and annoy­ance from these vehi­cles could lim­it the suc­cess of inte­grat­ing UAM into the trans­porta­tion sys­tem.” To reduce the impact of drones’ noise, plan­ning for their oper­a­tions requires an inno­v­a­tive approach and an impor­tant con­sid­er­a­tion for reg­u­la­tors.

Ion propul­sion tech­nolo­gies could make a dif­fer­ence since it offers unique oppor­tu­ni­ties in gen­er­at­ing silent thrust.  Most VTOL (ver­ti­cal take­off and land­ing) drones rely on high-speed rotors to gen­er­ate enough thrust to take off and stay in the air.

Mean­while, ion propul­sion is entire­ly elec­tric and pro­duces zero car­bon emis­sions. The process uses a high-volt­age elec­tric field to ion­ize the air mol­e­cules in the atmos­phere; the air mol­e­cules nat­u­ral­ly return to their orig­i­nal state after ion­iza­tion.

Cur­rent­ly, ion propul­sion is already used to keep com­mu­ni­ca­tion satel­lites prop­er­ly ori­ent­ed and to pro­pel deep-space probes. This tech­nol­o­gy pro­pels faster and for greater dis­tances. It’s also less expen­sive than any oth­er propul­sion tech­nol­o­gy cur­rent­ly avail­able.

On Earth, much larg­er amounts of the thrust are need­ed to over­come both grav­i­ty and the atmos­phere. If ion propul­sion is made viable for eVTOL oper­at­ing in the earth’s atmos­phere, it would be a game-chang­er in urban car­go deliv­ery.

The tech­nol­o­gy will inevitably affect indus­tries ver­ti­cal­ly and hor­i­zon­tal­ly across sec­tors, enhanc­ing the address­able mar­ket dra­mat­i­cal­ly. The chal­lenge is fas­ci­nat­ing and achiev­able from many oth­er per­spec­tives, includ­ing cre­at­ing, stor­age, inver­sion, and ther­mo­dy­nam­i­cal­ly effi­cient trans­mis­sion and dis­si­pa­tion of ener­gy.