The boom in lithium-ion battery technology—for electronics, power tools, and cars—provided an alternative to the large, noisy piston engines in small planes or screeching turbines in helicopters. Those batteries drive electric motors that are essentially silent.
But propellers slicing through the air remain the biggest source of noise. And electric power enables a bunch of engineering tricks to quiet them down. Nerd alert: Appreciating those tricks will require understanding a few engineering concepts, including disk loading, tip speed, and torque.
The article highlights several a wide range of aspects to low-volume electric flight: batteries, distributed propulsion, disk load, offset propeller speeds, shorter blades, weight, elevation, distance, and high-torque custom electric motors.
The article quotes not only Joby, but also Volocopter, Whisper, Archer, Lillium, and Kitty Hawk.
That final startup was founded by my old boss, Sebastian Thrun, who’s quoted in this article comparing the noise generated by his Heaviside eVTOL model to, “a flying hair dryer.” I love Sebastian.
Based on his work for Uber, Moore estimates that even a small vertiport might need a volume of 30 to 60 flights per hour to run in the black. [NB: Mark Moore spent decades at NASA, then four years at Uber Elevate, and now is the founder of Whisper.]
Which leads to:
“One of the great locations for vertiports is the top of a parking garage that’s right next to a highway, where the background noise level is 65 to 70 [decibels] at a hundred feet,” says Moore. “Because then you’re compatible with the neighborhood in terms of background noise level.”