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Comment by rob74 | Hacker News Reader

Probably not as bad as a helicopter? What is probably worse than with a helicopter however is the danger of accidents. The angle of the photo in the press release is weird, but here (https://www.airbus.com/en/innovation/low-carbon-aviation/urb...) the rotors seem to be at about the height of an adult's head.

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For a given amount of lift, all things being equal, a single larger diameter propellor will be quieter than several smaller ones at higher speeds, as most of the noise is from turbulence and a function of the difference in velocity between the air accelerated through the rotors and the ‘static’ air surrounding it.

In practice, the perceived noise is much (much) lower, basically inaudible: https://youtu.be/IX7rdJm5v6s?si=-eGOJKYidDWTRmHw&t=91

I should have said explicitly, rather the subsuming it in all else being equal, that it’s _very_ different between ‘multicopter’ mode and flying under a wing. The later is, of course, much mor efficient, and the propulsion is correspondingly much quieter.

How much of the noise of a helicopter is from the sonic booms of the rotor tips? I read somewhere it’s a substantial portion but I may be misremembering.

Very little, and rarely, if I understand correctly. The characteristic thwop-thwop noise of many helicopters is from the blade passing through the vortex created by the previous blade. In some circumstances, this might lead to local and intermittent supersonic flow, but it's not typical. I think it also only happens when the vehicle is moving in a particular way, but I don't know how vortices propagate from a rotor blade, so I couldn't say how or when the supersonic flow is most likely to occur.

And airliner engines, the old 737 for example, are even lower. That's why only ground crew approaches the aircraft, and that only after the engines stopped.

Yup, however airliners operate at airports, while this contraption is designed for "urban air mobility", whatever that means. I mean, it has to be something with looser restrictions than heliports, otherwise the niche for this vehicle would be pretty small...

EASA released regulation, and despite whatever companies want you make believe, Airbus being none of those, these aircraft are not allowed to land on a supermarket parking to fly you home. The operate from yet to be defined and built Vertiports (also airports and heliports and pads), for which the basic regulation is there.

Think helipads and not speeders on Coruscant.

Don't passengers have to approach the aircraft to board? From the picture, the only safe angle I see to board is from the front.

Electric engines can be stopped and started quickly and reliably, so they don't need to run while passengers are entered or exiting. This makes the vehicle much quieter and saves battery.

Sure, but then the engines are off. And some cones and such are placed to prevent people from stumbling into the blades.

Yeap, dangerous AF because of a failure to design from first principles.

See, Airbus does not have to design from first principle, they can do that from n-th principle. You know, like the difference between clueless amateurs and pros.

No! That's a terrible place to put a rotor!

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