EVTOL Noise: What's Possible? What's Hype?

[@zhihenglou]

| References | (Airbus Helicopters, 2015) www.airbushelicopters.com/website/en/press/Eco-friendly-and-eco-efficient-technologies-of-tomorrow-take-to-the-sky-with-Airbus-Helicopters%E2%80%99-Bluecopter-demonstrator_1801.html (Airbus, 2015) www.pressebox.com/pressrelease/eurocopter-deutschland-gmbh/Airbus-Helicopters-H160-Flight-Test-campaign-launched/boxid/743573 (Alvarez, 2019) kzbin.info/www/bejne/iX3Tn4l_d9WeptU&ab_channel=EduardoJ.Alvarez (Alvarez, 2021) kzbin.info/www/bejne/mpDCqIGqh651j5o&ab_channel=EduardoJ.Alvarez (Alvarez, 2022) kzbin.info/www/bejne/ooasqqeHrsd2prM&ab_channel=EduardoJ.Alvarez (Archer, 2021a) news.archer.com/how-loud-is-an-evtol (Archer, 2021b) news.archer.com/evtol-aircraft-vs-helicopters (Archer, 2022) kzbin.info/www/bejne/fp3Pp4Cnob6XZsU&ab_channel=Archer (Archer, 2024a) investors.archer.com/news/news-details/2024/Archer-Completes-Midnights-Transition-Flight/default.aspx (Archer, 2024b) kzbin.info/www/bejne/e3yqXmmorb10jqc (Arcosjet, 2024) kzbin.infouycqCgLWNpY (BMWGroup, 2022) www.press.bmwgroup.com/canada/article/detail/T0391113EN/the-new-bmw-3-series:-a-worldwide-success-story-in-its-seventh-generation-%E2%80%93-now-with-greater-appeal-than-ever?language=en (Cambridge, 2012) kzbin.info/www/bejne/i6KlnpeQYqeBn8k&ab_channel=CambridgeUniversity (Cape Copters, 2021) kzbin.info/www/bejne/l3aoYZp7qbOMiNE&ab_channel=CapeCopters (Cleveland Clinic, 2023) my.clevelandclinic.org/health/body/24642-tympanic-membrane-eardrum (Edwards, 2002) www.semanticscholar.org/paper/Revolutionary-Concepts-for-Helicopter-Noise-SILENT-Edwards-Cox/d1e9c24fd1ba6b7998a458c51737a643fe89f2c5 (Engys, 2021) engys.com/blog/fan-noise-simulation-using-helyx/ (EVTOL Research, 2024) kzbin.info/www/bejne/fHfKpnhopryDnM0&ab_channel=EVTOLresearch (First Principles, 2024) kzbin.info/www/bejne/oIPPZmasm7FladU&ab_channel=FirstPrinciples (Greenwood et al., 2022) readwise.io/reader/document_raw_content/200997778 (Harvard, 2018) kzbin.info/www/bejne/g3OzmWdnZayhm9U&ab_channel=HarvardNaturalSciencesLectureDemonstrations (Hughes, 2023) localnewsmatters.org/2023/06/29/cleared-for-takeoff-santa-cruz-based-evtol-firm-gets-faa-approval-to-begin-flight-testing/ (ICAS, 2012) www.icas.org/ICAS_ARCHIVE/ICAS2012/PAPERS/016.PDF (IFS, 2024) www.ifs.com/de/news/cloud/ifs-cloud-selected-by-joby (Jayaraman, 2024) www.researchgate.net/figure/EPNL-Calculation-Process_fig3_44226343 (Joby, 2021a) kzbin.info/www/bejne/fXnQiYVmrKeCn6s&ab_channel=JobyAviation (Joby, 2021b) kzbin.info/www/bejne/n6WzaWBpn5eIkKs&ab_channel=JobyAviation (Joby, 2021c) joby-site.cdn.prismic.io/joby-site/04f51a9c-10ca-4e4b-b6b8-c1729068e094_Aerodynamic-and-Aeroacoustic-Design-of-the-Joby-Propeller.pdf (Joby, 2021d) patents.google.com/patent/US20200269990A1 (Joby, 2022a) www.jobyaviation.com/news/joby-revolutionary-low-noise-footprint-nasa-testing/ (Joby, 2022b) www.jobyaviation.com/blog/joeben-invited-testify-congress-electric-noise/ (Joby, 2023a) kzbin.info/www/bejne/p2qQc6qIjK2UZqs&ab_channel=JobyAviation (Joby, 2023b) patents.google.com/patent/US20210253236A1/en?oq=US20210253236A1 (Joby, 2023c) kzbin.info/www/bejne/f4mao5eAopqpbNU&ab_channel=JobyAviation (Joby, 2023d) patents.google.com/patent/US20230322362A1/en?oq=US2023%2f0322362 (Joby, 2024a) www.jobyaviation.com/news/joby-demonstrates-potential-regional-journeys-landmark-hydrogen-electric-flight/ (Joby, 2024b) patentimages.storage.googleapis.com/64/b9/09/cdc5e0d88bc684/US20240233556A1.pdf (Joby, 2024c) kzbin.info/www/bejne/mmnFdKqMgqZ7gZo&ab_channel=JobyAviation (Joby, 2024d) www.jobyaviation.com/ (Khan Academy, 2014) kzbin.info/www/bejne/Y5Dbi42qbp6AsLs&ab_channel=khanacademymedicine (Matuszyk, 2013) www.researchgate.net/figure/Models-for-multipole-acoustic-sources_fig1_258904007 (Monson, 2007) www.researchgate.net/figure/A-typical-power-spectrum-of-fan-noise-consisting-of-both-broadband-and-tonal-noise_fig1_243584975 (Munro Live, 2024) kzbin.info/www/bejne/mYKpeWSQbqmAq7s&ab_channel=MunroLivekzbin.info/www/bejne/mYKpeWSQbqmAq7s&ab_channel=MunroLive (NASA, 2017) www.nas.nasa.gov/SC16/backgrounder_chaderjian_improving_flight.html (NPR, 2014) kzbin.info/www/bejne/pqmWoIl9jddno9E&ab_channel=NPR (OpenStax, 2016) openstax.org/books/university-physics-volume-1/pages/17-3-sound-intensity (Ramses de Looff, 2013) kzbin.info/www/bejne/qHTTi6OBj7GtZ5Y&ab_channel=RamsesdeLooff (Reed, 2022) www.aviationtoday.com/2022/03/14/the-quiet-evtol-revolution-designing-acoustics-for-public-acceptance/#:~:text=One%20factor%20that%20makes%20eVTOLs,is%20also%20different%2C%20says%20Page

[@rossnolan7283]

Excellent dissertation that does more to clarify the noise issue and measurement/metrics than any other i have seen. I will append my comments on it but firstly reiterate my basic thesis that they are all solving the wrong problem by focussing on vertical take off and landing per se and not seeking a better solution to the specific task of moving people, by air, in a built up environment ( with constraints of noise and cost,safety, air quality, etc and the sub issues of manufacturability and operation at a sufficient scale to really improve the traffic congestion issue that they espouse as their aim. The correct starting point ought to be the well established curves relating road traffic density versus both flow rate ( speed) and flow volume ( vehicle numbers per minute ) The total number of vehicles per minute is the crucial figure if any amelioration of congestion or even gridlock is to be acheived and occurs at a lower speed than the unimpeded travel speed limit so gives the most benefit to the most people overall. The most basic arithmetic shows that the existing flow volume is orders of magnitude greater than any conceivable evtol system could even make a measurable impact on ( around 5% of the "saturated' , but not jammed, flow rate needs to be removed to get back to free flowing conditions such is the non linearity of the flow versus density curve. The higher productivity of airborne vehicles makes each one equivalent to perhaps ten or more road vehicles if the appropriate infrastructure for evtol that will not be possible or tolerable. The only feasible way to have a viable air transit system for urban and suburban use is via ATOL or assisted take off and landing which fortunately, also solves the problem of noise ( being no noisier than the flying of a kite or winch launch of a sailplane and with no more need for brute power or disturbance than either (no hurricane level downwash etc) So the noise issue is best solved at it's root rather than trying to tame something that NEEDS hundreds or even thousands of installed horsepower just to get into the air at all. That is the most fundamental comment that bears on the noise issue. If a baby cannot sleep through such an aircraft taking off ot landing in the street outside then it is too loud ( there ARE no "100 metre" - radius - open spaces either in urban or suburban precincts to even make a noise level at that distance relevant , 20 metres might be suitable. (Or the noise of a modern ICE car say already acceptable ) Before i get onto a comment/ critique of your video i would point out that prior to the evtol craze there were two notable projects aimed at very large noise reduction in relatively small aircraft , by NACA in the lare 40s ysing a modifidd Stinson and in the 70s for the Vietnam war using modified SGS 2 32 sailplanes and ICE ('rattley' air cooled Lycomings even) that produced the quietest well tested aircraft yet. They were undetectable when flown on still nights only a few hundred feet above enemy troops and a quiet jungle background. Just to make the point again that by designing to NEED only low power the job is automatically easier than if you must go up ,and down at 90 degrees using sheer brute force - this approach can never be quiet. Critique; the examination of sound quality and quantity is excellent and gives a far clearer picture than the exagerrated and misleading misuse of figures by Joby and Archer et al - one other aspect is that sound from ABOVE is more perceived as 'bad' than from elsewhere because it is more likely to be a threat as felt by our more primitive brain areas (being pounced on ...) directionality matters. The turbulence into propellers issue is crucial to any downstream and in the case of Joby the rear props are working in the maelstrom coming from the front inners ( see their flow animations) Evtols have to somehow dissipate maybe 200 mph before landing at zero forward speed and ,like helicopters, will likely have to "flare" nose high to use lift braking which increase noise drastically, i used to live right next to a sports oval that doubled as as a helicopter medevac pad and my whole house shook when they arrived and did a landing over the roof in autogyro mode ( no hover ) to save time. Gentle hovering to and from ground is just too slow for any efficient turnaround. Blade twist is bad for hover efficiency bad essential for forward flight so both are compromised needing more power , downwash impinging on the wings and tail adds extra download and more power ( equalling the payload itself in the V22) Blowing a vee tail is a bad idea since a half a vee tail is no tail at all - several v tail glider accidents from control dis connects have shown this... on the other hand unblown tailsurfaces with the rest blown is also bad (electroair, Archer etc) control in gusty winds is not going to be good, carrying excess power and keeping some pitch in reserve for control might also add to noise. All in all vtol is a bad idea when what was wanted was to avoid needing a runway, or an airport, or any ground roll - not hovering for any useful end like a helicopter rescue etc ( for which battery evtols are no good) Hence the whole noise issue is a side effect of a basic conceptual flaw, it also requires six separate vehicles and six operators for every return trip (a commute say) and the logistics of organi,zing it all, car (taxi parking) and changeover spaces etc waiting rooms and so on as shown in the uber elevate videos. So noise might be a make or break issue but it is far from the only problem the evtol has. It could all end in tears 😢

[@rossnolan7283]

To add to my comments a bit, the ultra quiet Vietnam stealth aircraft were the Lockheed YO3a and the earlier QTs , basically powered sailplanes using minimum power to sustain flight by low span loading primarily, evtols and even estol are the worst possible application of battery power in terms of noise also. The 'tempo ' of operations is another noise annoyance factor as is the duration of the noise, airships operating from Melbourne got many noise complaints because of the length of time their lasted, helicopters ( mostly police) loitering circling also gets on the nerves. The Berlin airlift was a case in which non stop operations gave a taste of the projected Uber air intensity of turnarounds needed to get any profitability and the side effect on those near the flight paths. Having lived, in total, over seven years ON airports I am aware of the issue 😊 - there were videos by vtol research showing ca. 100 dBA for the Archer and earlier independent video/ audio from Marina airport of the Joby s4 which were anything but quiet, just hovering ( no climb power,) IN ground effect is the least bad case for noise, the "rear up' speed dissipating type landing is very much louder than hover transition and involves much blade stalling. Just listen to someone exercising a variable pitch propeller on run up to see the effect. Curfew will be imposed for any residential areas for certain, only ATOL can be installed or used in suburban locations ( using the free air space over the road and giving thereby immediate access to the roadway for departure and arrival as a road(able) vehicle, Note Bievert stating that his aim is to take people as close as possible to and from their destination and home - evtol is a failure at this and not least because of the turmoil and noise created plus the monumental overbearing structures required as vertiports/ pads unsuited to suburbia ( a see through cable array suffices for ATOL. The degree of unneccesary complication involved in evtol and extreme measures needed to shave weight etc eg by threeD printing parts, carbon autoclaving etc ( so admired strangely by production guru Sandy Munro) reminds me of the scene from raiders of the lost ark (?) where the king fu swordsman does his expert sword waving routine to which Indiana Jones just looks perplexed as he pulls out his gun, blows the guy away, and carries on... some expertise is just irrelevant to getting a job done...

[@springford9511]

Interesting video, thanks. Just want to point out that Helicopter buyers have already rejected quieter aircraft. The MD NOTAR aircraft are much quieter but are a commercial failure with very few sales. Looks like they are no longer available as a new purchase.

[@murrays9535]

Thanks John, and i agree there is great potential in eVTOL for noise reduction. You pointed out the difference in the ground cover between the EVTOL Research videos, but I thought you might have mentioned the Joby video of the hovering S4 measured from across a field of long grass - some of the best noise attenuation available. That was a dodgy marketing video! Also, the camera lens could well have foreshortened the distance from JoeBen to the aircraft, the aircraft be downwind of the measurement point and/or be at minimum gross weight. If they are so good, why spin 10X into a false claim of 100X or 1000X, improvement?

[@zhihenglou]

Thank you Murray, I am glad to hear from you again. I would add that Joby's aircraft measured 55dB at 100m in that particular video (see 0:56). But later communications by Joby state 65dB at 100m (see 57:44 or www.congress.gov/117/meeting/house/114372/witnesses/HHRG-117-PW05-Wstate-BevirtJ-20220317.pdf). Their current website states that their aircraft measures below 65dB at 100m (see www.jobyaviation.com/news/joby-revolutionary-low-noise-footprint-nasa-testing/). Cheers!

[@g.zoltan]

1:05 I want to discuss about this. Having studied aero engineering, I tried to create simple conceptual designs for EVTOL craft, just for amusement, but using very basic "napkin" calculations, I struggled to make aircraft concepts that would outperform a hypothetical heavyweight electrified helicopter. I wonder if my simple calculations are based on incorrect assumptions, or they show a valid criticism of the EVTOL industry. I'm mostly suspicious about my assumptions on distributed propulsion. It is hailed as a game changer, yet my basic calculations didn't yield meaningful gains over an equivalent setup of a larger laminar wing with a large single pusher prop. I'll have to review more literature on this topic, but until then I wonder if you have a take on this: do you think my results are plausible, or did I "fail the exam"?

[@DumbledoreMcCracken]

Jackpot

[@zhihenglou]

I think your results are plausible, assuming your performance criteria are payload, range, and endurance. In my view, distributed electric propulsion has overpromised and underdelivered on many aspects of aircraft design. Aircraft performance is one aspect where DEP promised improvements but has failed to deliver so far (on commercial planes). However, one aspect that DEP is legitimately useful for is aircraft control. I think drones or UAV’s demonstrate that DEP can be a very cost-effective solution for achieving VTOL capability and aircraft control during hover flight. This is my view on this question; I am curious to learn what other viewers think.

[@ZnOxide]

Is it about performance or noise? I’m confused about whether I’m missing something important about the topic.

[@g.zoltan]

@@ZnOxide Ok, let me try to remember. *My outcome parameter or optimization parameter is:* flight range, that's all. *My input parameter is:* battery weight. Outcome parameters are optimized for 3 battery weight inputs. *My boundary conditions were:* A fixed light payload, mandatory hover descent for X km's to simulate a sane takeoff/landing, Y minutes of reserve for hover flight, I think it was around 15minutes, well bellow the current helicopter requirement of 45minutes, a really optimistic structural efficiency model that assumes modern aircraft structures, Z meters of max wingspan to allow landing on existing helipads, simple conceptual deisign charts for stats (such as efficiency) of electric motors, batteries, propellers, airfoils, and basic fuselage geometries. *My variable parameters* are chosen freely to yield the best outcome parameter, these were: flight profile (ascent/descent), flight speed, wing geometry, and others.

[@ErnestMC]

Impressive analysis. Could you also include the effect of the turbines or engines as well. I think it is not only the aerodynamic noises buy the engines that contribute to the total.

[@zhihenglou]

Thanks, Ernest! I briefly mentioned combustion engines in this video but had to scope it out in order to keep this video within reasonable lengths. I think engines play a greater role in noise when you are sitting inside the plane. At further distances, propeller noise should be the dominant source still. But, like you say, engines play a role to the overall noise profile. I do not plan to talk about aircraft noise in the foreseeable future, so I hope someone else can pick up this subject. Cheers!

[@snekmeist1878]

Love your work

[@jfkastner]

Great Video! Any one of those 'Airtaxis' won't be able to provide mass service in Cities like New York - There is NOT enough ATC Traffic Guidance available, nor there are available 'Slots' at JFK or LGA, EWR etc. Since they are carrying Passengers you need advanced Tracking, Collision avoidance, Guidance, Weather etc - otherwise you endanger everyone.

[@rossnolan7283]

Sprinford, i worked on the prototype NOTAR when it was being developed in Australia by HawkerDeHavilland and felt it was not such a good idea then (1990s) with the main idea being to remove the danger of tail rotor strike or even stall , not so much noise.

[@ForbiddenMagic]

very comprehensive

[@TheBagOfHolding]

How would varied pitch affect the sound? I notice when they take off they are drastically pitched and not when they are displayed. They didn't let us hear it when they flew a pilot for a few seconds.

[@TheBagOfHolding]

You released it early! An early Christmas present to us. Thanks.

[@zhihenglou]

Thanks for coming by!

[@B0tch0]

That comment is not fake at all 🤣 Thank you deer KZbinr, I'm sure this video doesn't have alternative objectives.

[@rossnolan7283]

Fred... it seems to go unchallenged that an 'air taxi' ,of their kind, has to be completely different and MUCH bigger and heavier than an 'air car' would be whereas the ground taxi (or uber) will just be a regular mass production car simply repurposed as a for hire vehicle. Compare a typical modern four seat lightplane to any of these bloated monstrosities and ask why they are so much more costly and less range speed payload etc but get called 'advanced' as in AAM ... Indeed, a commutting aircraft ie fly to work, cannot be anything like these contraptions.

[@DumbledoreMcCracken]

The detectability of sound is not linear, and saying "1000 times quieter" is disingenuous at best, untruthful at worst. Sound must be 1/10 the pressure (or -10dBA) lower to be perceived at half the loudness (an oversimplification). So 1/1000 (or -30 dBA) the pressure is (1/2)^3, or 1/8th the loudness.

[@zhihenglou]

I would add a small correction: sounds must be 1/10 of the original *sound intensity* (or -10dBA) to be perceived at half the original loudness. In terms of sound pressure, this would would be around 1/3 of the original sound pressure. Cheers!

[@ridesnfights]

Toroidal propellers?

[@g.zoltan]

If they had benefits they would be used, or even just considered. But many years later, I' surprised someone even remembers that scam.

[@rossnolan7283]

Strange how a comprehensive comment just gets a ❤ or nothing at all. Whereas some trite line is responded in depth.. This phenomenon of a flood of money and simultaneous emergence of over 1100 designs with absolutely no actual demand or proven feasibility but an obscure report, sans data, by a financier house ( also underwriting the IPO ) leads to the expenditure of thousands of millions of dollars on speculative and inadequate aircraft by previously unexperienced 'entities' . Competent engineers and firms in the aircraft industry had explored this field and found the problems that these upstarts (start ups) are just repeating .. even Bievert should have known better from his mentor, Paul Moller's experience even if transposing the electric power and control from drone models (Canadian origin) might have simplified the task at the cost of almost no useful range or payload, savkng the planet from a non existent threat seems to justify all the cost and annoying side effects (eg noise) that must be paid by the misled public. Until the tunnell vision and blinding by greed runs it's course any questioning of the overall wisdom of evtol will be futile...

[@DanFrederiksen]

You forgot a key parameter. Vehicle mass. What joby and archer both did almost identically wrong. An autonomous single seater has much greater potential for low sound footprint and physical footprint to set down in urban areas. A particular win would be if such a vehicle will be allowed in the luxurious hills of los angeles so they can have little landing platform and go from their view to LAX or Van Nuys in mere seconds and board their plane. Or for that matter set down in beverly hills for a bit of shopping or brunch :) If an EVTOL can pick you up at a bar at 3am in the morning and take you home that has incomparably greater potential than the very conventional helicopter thinking that joby and archer are wasting billions on. And I have pointed this out for many years but nobody listens. They all know best and then they go bankrupt after wasting a billion effing dollars. If the world listened to me we would have star trek by now and that's not even an exaggeration.

[@TheBagOfHolding]

Id assume no payload and smaller battery but im the most skeptical person on the internet.